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Metagenomic Analysis of Bacterial and Fungal Communities Inhabiting Shiro Dominant Soils of Two Production Regions of Tricholoma Matsutake S. Ito & S. Imai in Korea

Forests 2021, 12(6), 758; https://doi.org/10.3390/f12060758
by Gi-Hong An, Jae-Han Cho, Ok-Tae Kim and Jae-Gu Han *
Reviewer 1: Anonymous
Reviewer 2: Anonymous
Reviewer 3: Anonymous
Forests 2021, 12(6), 758; https://doi.org/10.3390/f12060758
Submission received: 26 April 2021 / Revised: 3 June 2021 / Accepted: 4 June 2021 / Published: 9 June 2021
(This article belongs to the Section Genetics and Molecular Biology)

Round 1

Reviewer 1 Report

This work is to clarify the bacterial and fungal communities of shiro at the two different sites in South Korea. In the section of Introduction, authors noted that microbial communities in shiro soil had a high enzymatic activities involved in the degradation of organic carbon. This is not true for matsutake shiro because shiro is formed in nutrient poor soil in which forest litter and humus is not developed well.  So, nutrient dynamics in mycelial colony of matsutake is different from those of mat-forming mycorrhizal species reported by Trappe et al (2012) (doi:10.3390/d4020196).

The authors should note information on sampling site (latitude, longitude, height above sea level, soil type, and vegetation).  Also, date of sampling, the position of collection within a shiro and depth of collection point from the soil surface, because the activity of shiro is varied depending on the points within a shiro (Ohara and Hamada, 1967; Nature, 213, 528-529).  These data should be explained in the field researches.

 

Author Response

Thank you for valuable comments. We did our best to revise this manuscript according to reviewer's comment. Revised parts were remarked by blue color.

Once again, thank you for comments.

 

This work is to clarify the bacterial and fungal communities of shiro at the two different sites in South Korea. In the section of Introduction, authors noted that microbial communities in shiro soil had a high enzymatic activities involved in the degradation of organic carbon. This is not true for matsutake shiro because shiro is formed in nutrient poor soil in which forest litter and humus is not developed well.  So, nutrient dynamics in mycelial colony of matsutake is different from those of mat-forming mycorrhizal species reported by Trappe et al (2012) (doi:10.3390/d4020196).

> ANSWER: Thank you for this comment. We absolutely agreed with your comment. Please see line 41-45, and we added the reference.

The authors should note information on sampling site (latitude, longitude, height above sea level, soil type, and vegetation).  Also, date of sampling, the position of collection within a shiro and depth of collection point from the soil surface, because the activity of shiro is varied depending on the points within a shiro (Ohara and Hamada, 1967; Nature, 213, 528-529).  These data should be explained in the field researches.

> ANSWER: Thank you for this comment. Please see line 83-84, and 89-92. Soil properties, vegetation, etc. are not measured in this paper. However, this project containing this paper will be continued for five years, and we will be prepared for next paper. Your comment will be applied to next time.

Author Response File: Author Response.docx

Reviewer 2 Report

The topic addressed by the authors is interesting and the study has a merit, however, I think it is necessary to improved some parts of the manuscript. My comments are below.

ABSTRACT

Line 18
Please, explain the word „shiro” and then shiro+ and shiro-.

Lines 21-22
Authors’ wrote: „(…) microbial community in the T. matsutake dominant soils are closely associated with biotic factors and abiotic factors such as soil environments”.

Please, explain with which exactly biotic and abiotic factors the comminities are closely associated?
„Soil environments” is not very precise.

INTRODUCTION
In general, authors should describe briefly the background data for the distribution of T. matsutake (according to GBIF, it is Europe, Asia and North America; https://www.gbif.org/species/5241820 ), their symbiotic tree partners and the ecology of T. matsutake as an ectomycorrhizal species.

Lines 27-27
Authors’ wrote: „Tricholoma matsutake that form a symbiotic association with living root tips of Pinus densiflora”.

Please, explain that T. matsutake is associated with P. densiflora only, or with other Pinus/Pinaceae species.
According to UNITE database, T. matsutake can be associated with pines (e.g. P. densiflora,  P. sylvestris, P. pumila, P. nigra), other Pinaceae (Picea, Albies) and potentially with Fagales (Castanopsis, Quercus). Please, involve these data in the Introduction section.

(source:
https://unite.ut.ee/bl_forw_sh.php?sh_name=SH1647740.08FU#fndtn-panel1 )

Lines 32-33
Authors’ wrote: „However, the artificial cultivation of this fungus has not been established.”

As well as the most of ectomycorrhizal edible fungi, including Imleria badia, Boletus edulis, Cantharellus cibarius, Craterellus cornucopioides and other species.

Artificial cultivation is practicable for saprotrophic fungi such as shitake (Lentinula edode), Pleurotus, Flammulina or  Agaricus species. For ectomycorrhizal fungi, artificial cultivation is developed for a few hypogeous fungi (mostly Tuber species) only.

So, in the view of above, the lack of artificial cultivation of T.matsutake fits into the general trend for ectomycorrhizal fungi.

Lines 49-51
Authors’ wrote: „This revolutionary technology is superior to other sequencing methods because of its ability to rapidly process enormous amounts of DNA sequence data.”

I cannot agree. The assets of NGS sequencing are unquestionable, but this method has also a weak points, especially concerning ECM fungal speciec and therefore ECM fungal communities.

1. First, the sequences are quite short, so the species-level indentification of OTUs is often impossible.
2. Second, some fungal species/genera, which form the the abundant extramatrical hyphae (e.g. Atheliaceae such as Piloderma and Tylospora, but also Tricholoma), can be sequenced with better efficiency than other ECM fungi. In contrary, some fungal genera are more difficult to sequence because of their species-specific features (e.g. Cenococcum).
3. Third, for ectomycorrhizal fungal communities, the results of NGS of soil samples show a potential pule of symbionts in soil (including DNA of dead organism, spores ect), not those that actually form ECM symbiosis with trees.

Therefore the results of NGS sequencing cannot be considered as a  miraclous method that fixes everything. It isn't, even it the assets of the NGS  method are unquestionable.

For ECM fungal communities of T.matsutake, I suggest you analyse the ECM root tips on the pine roots and identify ECM fungal species from ECM roottips. It is more time-consuming method, but results are more precise and certain.

Studies of ECM communities using both NGS sequencing of soil and Sanger sequencing of ECM root tips show, that each method provides a large group of ECM fungal species. Moreover, the methods’ efficiency (NGS vs Sanger sequencing of ECM roottips) depends on the identity of ECM fungal species at higher taxonomic lever (genera, family, order, phylogenetic lineage ect).

Lines 61-64
Authors’ wrote: „However, the yields of T. matsutake in Gyeongsangbuk-do province has been gradually decreasing, and KOSIS was revealed that the yields of T. matsutake in Gyeongsangbuk-do province in 2007 was 340 tons, but it was 75 tons in 2017.”

Similar decrease is observed in the production of Tuber melanosporum in souther Europe, what is caused by climate change (Thomas, Büntgen 2019 DOI : https://doi.org/10.1016/j.scitotenv.2018.11.252 ).

I suggest you to involve the issue of climate change into Introduction and Discussion sections. See Guo et al. 2017, DOI: https://www.nature.com/articles/srep46221

Moreover, I think the lines 57-75 dedicated to the decrease in T. matsutake crop should be moved to the place before the description of NGS method (lines 45-56).

METHODS

Here I have two general comments:
- are the two sites enough for any general conclusions? Especially, that the results obtained from two geographical locations are highly varied. If there is any pattern in shiro+ vs shiro- fungal communities, these results cannot show it.
- Line 94, authors’ wrote: "microbial DNA was extracted from 0.5 – 1 g per soil using a DNeasy"

How much exactly? Mean and SD? Authors should describe, how they treated the soil before the DNA extraction. (For example, were the soil mixed before DNA extraction? How much, how long, in what way?)

It is crucial step, because „what you put into is what you get out of it”. Especially for NGS sequencing.

RESULTS
In the section „3.4. Relative abundance of fungal communities” authors omit the trophic status of fungal OTUs in the fungal communities.

Tricholoma species are ectomycorrhizal fungus, so I strongly reccomand the independent analyses of ECM fungal OTUs and other fungal OTUs (mostly saprotrophs). The ECM and saprotrophic fungal communities are drived by different environmental variables, and, most problaby, are shaping under different patterns (see Kujawska et al. 2021 https://www.mdpi.com/1999-4907/12/3/353 )

Authors can assigned the OTUS to the trophic groups based on FUNGuild, or the phylogenetic lineages of ectomycorrhizal fungal genera  (see Tedersoo et al. 2010 https://doi.org/10.1007/s00572-009-0274-x )

I ve noticed, that in the Table S2 authors listed a numerous ECM fungal species/genera: Tricholoma matsutake, Tricholoma saponaceum, Tylospora sp, Astraeus sp, Sistotrema sp, Russula nigricans, Sebacina candida, Sebacina sp and Tomentella sp. Additionally, they have found ericoid mycorrhizal OTUs: Oidiodendron sp.

DISCUSSION
The role of bacteria in forming of ECM fungal sporocarps is well-studied and described for truffles (genera Tuber). I suggest you to mention a bacterial-based studies of truffle’ frutification.

Lines 296-299
Authors’ wrote: „There are some observations that the sites of occurrence of T. matsutake have low fungal diversity suggested that the mycelia of T. matsutake form fruiting bodies under little competitions with other microoganisms,”

First of all, Tricholoma matsutake is an ectomycorrhizal fungal species, so could compete with other ECM fungal species.

Moreover, I ve noticed, that in the Table S2, the sum of percent contribution of fungal OTUs is highly varied. In shiro+ soils it is 97%, however, in shiro- soils it is 87% in Yangyang, and 46% in Bonghwa.

For bacterial OTUs, the differences are similar: in shiro+ soils, the sum of percent contribution of bacterial OTUs ranged from 71 to 76%, but for shiro- soils it is only a 11 and 26%.

Please explain, where’s the rest of fungal and bacterial OTUs from shiro- soils.
More than 50% of fungal OTUs (shiro- soils, Bonghwa) and more than 70% of bacterial OTUs (shiro- soils; Yangyang and Bonghwa) are missing in the Tables S1 and S2. A little bit curious, isn’t it?

Finally, I suggest the authors to make clear the research questions and the gaps of knowlege, which are revealed by this studies. That might be the strength of this publication.

Author Response

Thank you for valuable comments. We did our best to revise this manuscript according to reviewer's comment. Revised parts were remarked by red color.

Once again, thank you for comments.

 

The topic addressed by the authors is interesting and the study has a merit, however, I think it is necessary to improved some parts of the manuscript. My comments are below.

ABSTRACT

Line 18
Please, explain the word „shiro” and then shiro+ and shiro-.

> ANSWER: Thank you for this comment. Please see line 92-93.

 

Lines 21-22
Authors’ wrote: „(…) microbial community in the T. matsutake dominant soils are closely associated with biotic factors and abiotic factors such as soil environments”.

Please, explain with which exactly biotic and abiotic factors the comminities are closely associated?
„Soil environments” is not very precise.

> ANSWER: Thank you for this comment. We have revised it. Please see line 22.

 

INTRODUCTION
In general, authors should describe briefly the background data for the distribution of T. matsutake (according to GBIF, it is Europe, Asia and North America; https://www.gbif.org/species/5241820 ), their symbiotic tree partners and the ecology of T. matsutake as an ectomycorrhizal species.

Lines 27-27
Authors’ wrote: „Tricholoma matsutake that form a symbiotic association with living root tips of Pinus densiflora”.

Please, explain that T. matsutake is associated with P. densiflora only, or with other Pinus/Pinaceae species.
According to UNITE database, T. matsutake can be associated with pines (e.g. P. densiflora P. sylvestris, P. pumila, P. nigra)other Pinaceae (Picea, Albies) and potentially with Fagales (Castanopsis, Quercus). Please, involve these data in the Introduction section.

(source:
https://unite.ut.ee/bl_forw_sh.php?sh_name=SH1647740.08FU#fndtn-panel1 )

> ANSWER: Thank you for this comment. We absolutely agreed with your comment. As see the global perspective, it is fact that T. matsutake form not only a symbiotic association with Pinus densiflora but also other pine (P. sylyestris, P. pumila, P. nigra), and other Pinaceae (Picea, Albies). However, we have a focus in regions in Korea (please see line 2; ~ rural communities in Korea). In Korea, the mountain of T. matsutake producing regions mainly occupy more than 80% of P.densiflora vegetation. So we was written as P.densiflora.

 

Lines 32-33
Authors’ wrote: „However, the artificial cultivation of this fungus has not been established.”

As well as the most of ectomycorrhizal edible fungi, including Imleria badia, Boletus edulis, Cantharellus cibarius, Craterellus cornucopioides and other species.

Artificial cultivation is practicable for saprotrophic fungi such as shitake (Lentinula edode), PleurotusFlammulina or  Agaricus species. For ectomycorrhizal fungi, artificial cultivation is developed for a few hypogeous fungi (mostly Tuber species) only.

So, in the view of above, the lack of artificial cultivation of T.matsutake fits into the general trend for ectomycorrhizal fungi.

> ANSWER: Thank you for this comment. We absolutely agreed with your comment that the study of artificial cultivation of T. matsutake fits into the general trend for ectomycorrhizal fungi. However, unlike other ectomycorrhizal mushrooms, T. matsutake have not only been studied for artificial cultivation for a long time in Korea, China, and Japan, but are also traded at high prices compared to other mushrooms. So We think that the study for artificial cultivation of T. matsutake may be more important than other ectomycorrhizal mushrooms, and provided great benefits to rural communities in Korea.

 

Lines 49-51
Authors’ wrote: „This revolutionary technology is superior to other sequencing methods because of its ability to rapidly process enormous amounts of DNA sequence data.”

I cannot agree. The assets of NGS sequencing are unquestionable, but this method has also a weak points, especially concerning ECM fungal speciec and therefore ECM fungal communities.

1. First, the sequences are quite short, so the species-level indentification of OTUs is often impossible.
2. Second, some fungal species/genera, which form the the abundant extramatrical hyphae (e.g. Atheliaceae such as Piloderma and Tylospora, but also Tricholoma), can be sequenced with better efficiency than other ECM fungi. In contrary, some fungal genera are more difficult to sequence because of their species-specific features (e.g. Cenococcum).
3. Third, for ectomycorrhizal fungal communities, the results of NGS of soil samples show a potential pule of symbionts in soil (including DNA of dead organism, spores ect), not those that actually form ECM symbiosis with trees.

Therefore the results of NGS sequencing cannot be considered as a  miraclous method that fixes everything. It isn't, even it the assets of the NGS method are unquestionable.

For ECM fungal communities of T.matsutake, I suggest you analyse the ECM root tips on the pine roots and identify ECM fungal species from ECM roottips. It is more time-consuming method, but results are more precise and certain.

 

Studies of ECM communities using both NGS sequencing of soil and Sanger sequencing of ECM root tips show, that each method provides a large group of ECM fungal species. Moreover, the methods’ efficiency (NGS vs Sanger sequencing of ECM roottips) depends on the identity of ECM fungal species at higher taxonomic lever (genera, family, order, phylogenetic lineage ect).

> ANSWER: Thank you for this comment. We absolutely agreed with your comment. We have revised it. Please see line 57-60. We added the reference. It is fact that there are distinct advantages and limitations for NGS technology. However, it must be the technology that can process the largest amount of data at fastest and cheapest among existing technologies. We discussed in section of Discussion, and please see line 367-372. Moreover, this project containing this paper will be continued for five years, and we will be prepared for next paper. Your comments will be applied to next paper. We’ll make sure to refer to it. Thank you.

 

Lines 61-64
Authors’ wrote: „However, the yields of T. matsutake in Gyeongsangbuk-do province has been gradually decreasing, and KOSIS was revealed that the yields of T. matsutake in Gyeongsangbuk-do province in 2007 was 340 tons, but it was 75 tons in 2017.”

Similar decrease is observed in the production of Tuber melanosporum in souther Europe, what is caused by climate change (Thomas, Büntgen 2019 DOI : https://doi.org/10.1016/j.scitotenv.2018.11.252 ).

I suggest you to involve the issue of climate change into Introduction and Discussion sections. See Guo et al. 2017, DOI: https://www.nature.com/articles/srep46221

MoreoverI think the lines 57-75 dedicated to the decrease in T. matsutake crop should be moved to the place before the description of NGS method (lines 45-56).

> ANSWER: Thank you for this comment. We absolutely agreed with your comment. However, we are not measured and cannot showing any data related with the climate change in this time. Although your suggestion that the issue of climate change add into Introduction and Discussion sections, are very reasonable to explain about the decrease of the production of T. matsutake at Bonghwa site in Korea, your comment will be applied to next paper. We’ll make sure to refer to it. Moreover, we decided that the current state is suitable for storytelling of this paper. Thank you.

 

METHODS

Here I have two general comments:
- are the two sites enough for any general conclusions? Especially, that the results obtained from two geographical locations are highly varied. If there is any pattern in shiro+ vs shiro- fungal communities, these results cannot show it.

> ANSWER: Thank you for this comment. We absolutely agreed with your comment. Please see line 375-401. In this paper, we hypothesized that the microbial community in the production soils of T. matsutake will be quite similar to each other regardless of geographical characteristics, if there are microorganisms that have beneficial effects on the growth of mycelium and the formation of fruit body of T. matsutake. However, there are low-similarity among microbial communities of shiro+ soil. We added some explanations for low-similarity in Discussion section.


- Line 94, authors’ wrote: "microbial DNA was extracted from 0.5 – 1 g per soil using a DNeasy"

How much exactly? Mean and SD? Authors should describe, how they treated the soil before the DNA extraction. (For example, were the soil mixed before DNA extraction? How much, how long, in what way?)

It is crucial step, because „what you put into is what you get out of it”. Especially for NGS sequencing.

> ANSWER: Thank you for this comment. We absolutely agreed with your comment. First of all, by using a soil sampler, soils containing shiro (shiro+) were collected in 10 cm depth from the soil surface on 3 point of the zone of beneath of T. matsutake. Soil samples put into polyvinyl bag and mixed. After soil sampling, soil samples immediately move to ice box, and move to Laboratory, keeping them frozen as much as possible. Some of the samples that have been transferred to the laboratory, have been frozen and moved to the analysis center for NGS.

 

RESULTS
In the section „3.4. Relative abundance of fungal communities” authors omit the trophic status of fungal OTUs in the fungal communities.

Tricholoma species are ectomycorrhizal fungus, so I strongly reccomand the independent analyses of ECM fungal OTUs and other fungal OTUs (mostly saprotrophs). The ECM and saprotrophic fungal communities are drived by different environmental variables, and, most problaby, are shaping under different patterns (see Kujawska et al. 2021 https://www.mdpi.com/1999-4907/12/3/353 )

Authors can assigned the OTUS to the trophic groups based on FUNGuild, or the phylogenetic lineages of ectomycorrhizal fungal genera  (see Tedersoo et al. 2010 https://doi.org/10.1007/s00572-009-0274-x )

I ve noticed, that in the Table S2 authors listed a numerous ECM fungal species/genera: Tricholoma matsutakeTricholoma saponaceumTylospora sp, Astraeus sp, Sistotrema sp, Russula nigricansSebacina candidaSebacina sp and Tomentella sp. Additionally, they have found ericoid mycorrhizal OTUs: Oidiodendron sp.

> ANSWER: Thank you for this comment. We absolutely agreed with your comment. Please see line 328-332. We added some discussion.



DISCUSSION
The role of bacteria in forming of ECM fungal sporocarps is well-studied and described for truffles (genera Tuber). I suggest you to mention a bacterial-based studies of truffle’ frutification.

> ANSWER: Thank you for this comment. The objective of this paper is to determine the differences of microbial communities in soils where T. matsutake occurs two different sites. We sorry that your suggestion about bacterial-based studies of truffle’s fruification, may be useful as bacterial functional profiles related with the occurrence of T. matsutake when the bacterial community will be clearly determined of our sites. We’ll make sure to refer to it. Thank you.

 

Lines 296-299
Authors’ wrote: „There are some observations that the sites of occurrence of T. matsutake have low fungal diversity suggested that the mycelia of T. matsutake form fruiting bodies under little competitions with other microoganisms,”

First of all, Tricholoma matsutake is an ectomycorrhizal fungal species, so could compete with other ECM fungal species.

Moreover, I ve noticed, that in the Table S2, the sum of percent contribution of fungal OTUs is highly varied. In shiro+ soils it is 97%, however, in shiro- soils it is 87% in Yangyang, and 46% in Bonghwa.

For bacterial OTUs, the differences are similar: in shiro+ soils, the sum of percent contribution of bacterial OTUs ranged from 71 to 76%, but for shiro- soils it is only a 11 and 26%.

Please explain, where’s the rest of fungal and bacterial OTUs from shiro- soils.
More than 50% of fungal OTUs (shiro- soils, Bonghwa) and more than 70% of bacterial OTUs (shiro- soils; Yangyang and Bonghwa) are missing in the Tables S1 and S2. A little bit curious, isn’t it?

> ANSWER: Thank you for this comment. We absolutely agreed with your comment. Please see line 208-224, and 386-393. We revised Table S1 and S2.


Finally, I suggest the authors to make clear the research questions and the gaps of knowlege, which are revealed by this studies. That might be the strength of this publication.

> ANSWER: Thank you for this comment. We will try to make up for the shortcomings of this study and to write better papers in the next study. 

Author Response File: Author Response.docx

Reviewer 3 Report

The manuscript entitled "Metagenomic analysis of bacterial and fungal communities inhabiting shiro dominant soils of two production regions of Tricholoma matsutake in Korea" is an interesting analysis of the two different soil samples (named shiro+ and shiro-) from two different locations using NGS sequencing. However, the description of methods should be definitely improved before possible publication.

The Authors sample two sites, but the desription of sampling is not clear: did you sample one shiro+ and one shiro- sample or several subsamples per each site? Then, DNA was isolated once per each soil sample? Current description of sampling and DNA extraction, library construction etc., strongly suggest that the experiment has no replicates at any stage, which is unacceptable.

You can't build any discussion based on analysis of only two pairs of samples. No global conclusions could be made based only on these data.

Line 102: I believe that there should be "25 cycles of .." not "25° cycles of...". 

Lines 103-105: Was the efficciacy of 1st PCR similar among all of the reactions? You wrote that in the 2nd PCR you used 2ul of the purified product of 1st PCR. Why you quantified only the input for 1st PCR?

About the results (both bacteria and fungi): I do not feel that using amplicon sequencing you could characterize the biodiversity on the species level. In my opinion the fragment used for sequencing is too short for such analysis. For example if you want to identify some species, like Pseudomonas you should use more than one marker gene (four is nice). During amplicon analysis only fragment of one gene or one region is used. It is safer to analyse the diversity on some upper levels like genus.

Figure 3a - please try to change the colour palette. It is hard to distinguish between the blues and purples.

In fact, the whole manuscript is based only on the biodiversity analysis made with NGS. It would be nice if the authors could confirm those results with other methods, like qPCR or some diversity analysis based on RNA. The presented descritpion is just the potential of the environment, using other methods should show the active genus/species which could have a real impact on the environment and Tricholoma matsutake production.

Author Response

Thank you for valuable comments. We did our best to revise this manuscript according to reviewer's comment. Revised parts were remarked by red color.

Once again, thank you for comments.

 

The manuscript entitled "Metagenomic analysis of bacterial and fungal communities inhabiting shiro dominant soils of two production regions of Tricholoma matsutake in Korea" is an interesting analysis of the two different soil samples (named shiro+ and shiro-) from two different locations using NGS sequencing. However, the description of methods should be definitely improved before possible publication.

The Authors sample two sites, but the desription of sampling is not clear: did you sample one shiro+ and one shiro- sample or several subsamples per each site? Then, DNA was isolated once per each soil sample? Current description of sampling and DNA extraction, library construction etc., strongly suggest that the experiment has no replicates at any stage, which is unacceptable.

You can't build any discussion based on analysis of only two pairs of samples. No global conclusions could be made based only on these data.

> ANSWER: Thank you for this comment. We absolutely agreed with your comment. Please see line 89-93. As replicates, soil samples containing shiro+ and shiro- and were collected in 10 cm depth from the soil surface on 3 spots of the zone of beneath of T. matsutake. Also, please see line 394-398 in discussion section. We hope you will understand that this study was the first year of the project and it was different to sampling at many points without the favorable permissions from famers in the first year. Moreover, this project containing this paper will be continued for five years, and we will be prepared for next paper that many sampling point added. Your comments will be applied to next paper. We’ll make sure to refer to it. Thank you.

Line 102: I believe that there should be "25 cycles of .." not "25° cycles of...". 

> ANSWER: Thank you for this comment. We have revised it.

Lines 103-105: Was the efficciacy of 1st PCR similar among all of the reactions? You wrote that in the 2nd PCR you used 2ul of the purified product of 1st PCR. Why you quantified only the input for 1st PCR?

> ANSWER: Thank you for this comment. The condition for 2nd PCR was same as the 1st PCR condition as well as PCR product according to the manufacturer’s instructions.

About the results (both bacteria and fungi): I do not feel that using amplicon sequencing you could characterize the biodiversity on the species level. In my opinion the fragment used for sequencing is too short for such analysis. For example if you want to identify some species, like Pseudomonas you should use more than one marker gene (four is nice). During amplicon analysis only fragment of one gene or one region is used. It is safer to analyse the diversity on some upper levels like genus.

> ANSWER: Thank you for this comment. We absolutely agreed with your comment. We discussed in section of Discussion, and please see line 389-394. We added the reference. It is fact that some species was not enough for identify the species level due to the NGS limitation. However, it must be the technology that can process the largest amount of data at fastest and cheapest among existing technologies. We also feel that it must be necessary to combine with analysis for the long read lengths like Sanger sequencing method. Moreover, this project containing this paper will be continued for five years, and we will be prepared for next paper. Your comments will be applied to next paper. We’ll make sure to refer to it. Thank you.

 

Figure 3a - please try to change the colour palette. It is hard to distinguish between the blues and purples.

> ANSWER: Thank you for this comment. Please see figure 3a. We have revised it.

 

In fact, the whole manuscript is based only on the biodiversity analysis made with NGS. It would be nice if the authors could confirm those results with other methods, like qPCR or some diversity analysis based on RNA. The presented descritpion is just the potential of the environment, using other methods should show the active genus/species which could have a real impact on the environment and Tricholoma matsutake production.

> ANSWER: Thank you for this comment. We absolutely agreed with your comment. There are some limitations to be supplemented in the current paper. Nevertheless, we thought that our resulting about microbial community differed within/across the sites, may be provided important information to contribute toward an expanding foundation for knowledge on the microbial community in habitats of T. matsutake. Furthermore, we must be need to suitable analysis of methods and many information about biotic and abiotic factors from the various sites and regions to clarify the change of microbial community in dominant soils of T. matsutake.

Author Response File: Author Response.docx

Round 2

Reviewer 2 Report

In general, I am still not sure, that the two sites are enough for any conclusions. The “low-similarity among microbial communities of shiro+ soil.” may be caused by the inappropriate sampling.

The description of study sites is insufficient, as well as the description of methods. Both should be improved.

The reference list should be improved according to the current state of knowledge and with particular emphasis on the good papers published in renowned journals.  Other studies of fungal communities with the application NGS methods should be involved, as well as the standard methods used to data analysis in such studies.

Authors should pay more attention to the trophic modes/groups of identified OTUs. First of all, the contribution of ECM OTUs vs any other fungal OTUs. In Fig. 4, ECM genera are mixed with saprotrophic genera. At the trophic level, some similarities can be found:

B_Shiro+ : 62% T. matsutake, 2% other ECM, 32% other fungi, 3% unknown
Y_Shiro+ : 68% T. matsutake, 3% other ECM, 25% other fungi, 3% unknown

B_Shiro- : 0% T. matsutake, 35% other ECM, 28% other fungi, 37% unknown
Y_Shiro- : 0% T. matsutake, 31% other ECM, 58% other fungi, 11% unknown

Please, read carefully the comments of Reviewer 3. I fully agree with these valuable remarks.

Detailed comments below

ABSTRACT
Line 18
Please, explain the words „shiro+” and shiro- in the Abstract. 
Please, add in the Abstract this information:
"T. matsutake production soil (shiro+ soil) and nonproduction soil (shiro- soil)"

INTRODUCTION
Authors’ wrote: „ In Korea, the mountain of T. matsutake producing regions mainly occupy more than 80% of P.densiflora vegetation. So we was written as P.densiflora.”.

Please, describe the tree vegetation in the study sites, with the particular emphasis on these trees, which potentially can be a ECM partner of T. matsutake (e.g. other Pine species).

Lines 57-58
Authors’ wrote: „ this technology is still more useful than other previous sequencing methods.”

Its not true. 

As noted by the Reviewer 3, the results of NGS sequencing provide a short sequences. Thus OTUs - operational taxonomic units, cannot be treated as not equal to species, in contrary to the long sequences (>600 bp) obtained from Sanger sequencing of ITS and/or LSU regions of rDNA. 

I fully agree with the comment of Reviewer 3: “It is safer to analyse the diversity on some upper levels like genus.”

Lines 61-64
Authors’ wrote: „However, the yields of T. matsutake in Gyeongsangbuk-do province has been gradually decreasing, and KOSIS was revealed that the yields of T. matsutake in Gyeongsangbuk-do province in 2007 was 340 tons, but it was 75 tons in 2017.”

I think, authors should mention the impact of climate change on the efficiency of fungal fruit bodies production, cause the decreasing in ECM fungal fruit bodies production (mentioned for T. matsutake) is known to be caused by climate change. It is well-studied for truffles just because truffles are very expensive, but similar trends can be observed for other ECM fungal species. Moreover, the decrease in area of high suitable niches is already predicted for T. matsutake in China. ( Guo et al. 2017 https://www.nature.com/articles/srep46221  )

Authors should mention this issue, because in view of the above the importance of this studies increasing.

Author Response

Thank you for valuable comments. We did our best to revise this manuscript according to reviewer's comment. Revised parts were remarked by red color.

Once again, thank you for comments.

 

 

In general, I am still not sure, that the two sites are enough for any conclusions. The “low-similarity among microbial communities of shiro+ soil.” may be caused by the inappropriate sampling.

The description of study sites is insufficient, as well as the description of methods. Both should be improved.

The reference list should be improved according to the current state of knowledge and with particular emphasis on the good papers published in renowned journals.  Other studies of fungal communities with the application NGS methods should be involved, as well as the standard methods used to data analysis in such studies.

Authors should pay more attention to the trophic modes/groups of identified OTUs. First of all, the contribution of ECM OTUs vs any other fungal OTUs. In Fig. 4, ECM genera are mixed with saprotrophic genera. At the trophic level, some similarities can be found:

B_Shiro+ : 62% T. matsutake, 2% other ECM, 32% other fungi, 3% unknown
Y_Shiro+ : 68% T. matsutake, 3% other ECM, 25% other fungi, 3% unknown

B_Shiro- : 0% T. matsutake, 35% other ECM, 28% other fungi, 37% unknown
Y_Shiro- : 0% T. matsutake, 31% other ECM, 58% other fungi, 11% unknown

> ANSWER: Thank you for this comment. We absolutely agreed with your comment. We revised in results and discussion section including Table S1 and 2.

Please, read carefully the comments of Reviewer 3. I fully agree with these valuable remarks.

Detailed comments below

ABSTRACT
Line 18
Please, explain the words „shiro+” and shiro- in the Abstract. 
Please, add in the Abstract this information:
"T. matsutake production soil (shiro+ soil) and nonproduction soil (shiro- soil)"

> ANSWER: Thank you for this comment. Please see line 14-17.



INTRODUCTION
Authors’ wrote: „ In Korea, the mountain of T. matsutake producing regions mainly occupy more than 80% of P.densiflora vegetation. So we was written as P.densiflora.”.

Please, describe the tree vegetation in the study sites, with the particular emphasis on these trees, which potentially can be a ECM partner of T. matsutake (e.g. other Pine species).

> ANSWER: Thank you for this comment. Please see line 82-90 and Table 1.



Lines 57-58
Authors’ wrote: „ this technology is still more useful than other previous sequencing methods.”

Its not true. 

As noted by the Reviewer 3, the results of NGS sequencing provide a short sequences. Thus OTUs - operational taxonomic units, cannot be treated as not equal to species, in contrary to the long sequences (>600 bp) obtained from Sanger sequencing of ITS and/or LSU regions of rDNA. 

I fully agree with the comment of Reviewer 3: “It is safer to analyse the diversity on some upper levels like genus.”

> ANSWER: Thank you for this comment. We absolutely agreed with your comment. We have omitted and revised in results and discussion section. We added the references recommended in your advises.

Lines 61-64
Authors’ wrote: „However, the yields of T. matsutake in Gyeongsangbuk-do province has been gradually decreasing, and KOSIS was revealed that the yields of T. matsutake in Gyeongsangbuk-do province in 2007 was 340 tons, but it was 75 tons in 2017.”

I think, authors should mention the impact of climate change on the efficiency of fungal fruit bodies production, cause the decreasing in ECM fungal fruit bodies production (mentioned for T. matsutake) is known to be caused by climate change. It is well-studied for truffles just because truffles are very expensive, but similar trends can be observed for other ECM fungal species. Moreover, the decrease in area of high suitable niches is already predicted for T. matsutake in China. ( Guo et al. 2017 https://www.nature.com/articles/srep46221  )

> ANSWER: Thank you for this comment. We absolutely agreed with your comment. We have revised results and discussion section. We added the references.

 

Authors should mention this issue, because in view of the above the importance of this studies increasing.

Author Response File: Author Response.docx

Reviewer 3 Report

Material and Methods - Libraries construction:
I was not asking directly about the second PCR conditions but about the amount of template used for the second PCR. In the manuscript it is written that 2ul were used (line 111). I'm asking about the concentration of this template. It is important to compare things.  2 ul of 10 ng/ul DNA as an imput is not the same as 2 ul of 50 ng/ul DNA as an imput. The amounts of tempaltes used in second PCR should be comparable/uniform among all the reactions at this stage. Did you measure the concentrations of the purified 1st PCR products or just used 2 ul of them as a templates?
Results - The taxonomic description of bacterial and fungal communities
Once again, you can not write about the diversity on specie level because it is not confirmed (and it needs confirmation). The changes made to this part of the manuscript are insufficient. Please describe the diversity on genus level instead specie level. Then it will be OK. The probability of incorrect classification on genus level is smaller than on specie level.

Author Response

Thank you for valuable comments. We did our best to revise this manuscript according to reviewer's comment. Revised parts were remarked by red color.

Once again, thank you for comments.

 

 

Material and Methods - Libraries construction:
I was not asking directly about the second PCR conditions but about the amount of template used for the second PCR. In the manuscript it is written that 2ul were used (line 111). I'm asking about the concentration of this template. It is important to compare things.  2 ul of 10 ng/ul DNA as an imput is not the same as 2 ul of 50 ng/ul DNA as an imput. The amounts of tempaltes used in second PCR should be comparable/uniform among all the reactions at this stage. Did you measure the concentrations of the purified 1st PCR products or just used 2 ul of them as a templates?

> ANSWER: Thank you for this comment. We absolutely agreed with your comment. Pleased see materials and methods sections.


Results - The taxonomic description of bacterial and fungal communities
Once again, you can not write about the diversity on specie level because it is not confirmed (and it needs confirmation). The changes made to this part of the manuscript are insufficient. Please describe the diversity on genus level instead specie level. Then it will be OK. The probability of incorrect classification on genus level is smaller than on specie level.

> ANSWER: Thank you for this comment. We absolutely agreed with your comment. We revised from species levels to genus levels of results and discussion section including Table 4, Table 5, Table S1 and S2.

Author Response File: Author Response.docx

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