Microbial Degradation of (Micro)plastics: Mechanisms, Enhancements, and Future Directions

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

In the reviewed article Authors discussed the current and extremely important problem of widespread environmental pollution the by (micro)plastics. Authors reviewed and discussed the newest research results concerning the possibilities of using microorganisms and the biochemical processes to degrade microplastics. The manuscript is well prepared, clearly written, quite comprehensive, relevant for the field ,and presented in a well-structured manner.  The cited references are mostly (over 75%) recent publications (within the last 5 years) and relevant to the field. The statements and conclusions drawn are coherent and supported by the listed citations and the presented figures and tables are appropriate and easy to understand.

While other similar literature reviews were published in the last two years, this review is most likely the first to include results of research of ‘coupled enhanced technologies’ – combination of physico-chemical and biological methods of microplastics degradation. Therefore, I believe that the current review is still relevant and of interest to the scientific community.

However, there are still some things and sentences that require improvement:

-          Line 29: perhaps word ‘significant’ instead of 'vital' would be better

-          Line 37: word 'stability’ is not entirely understandable, perhaps word '’longevity’ or ‘durability’ would be more correct

-          Table 2. What are ‘strokes/min’? Perhaps Authors meant ‘rpm’?

-          Line 167: citation [50] is incorrect

-          Line 183: font used for Latin names is in different size than the rest of the line

-          Lines 188-193: Latin names should be written in italics

-          Table 4, lines 2 and 3, plastic weight loss data are missing; if they are not reported please add ‘not reported’ or ‘not available’

-          Line 238: I am not certain that the name used in the subtitle is correct. Genetic engineering technology is not an augmentation technology. Perhaps the technologies presented in this subchapter could be named ‘Coupled enhanced technologies’?

-          Line 341: it should be  ‘Available online’, not ’Availabie online’

Comments on the Quality of English Language

-          Line 29: perhaps word ‘significant’ instead of 'vital' would be better

-          Line 37: word 'stability’ is not entirely understandable, perhaps word '’longevity’ or ‘durability’ would be more correct

-          Table 2. What are ‘strokes/min’? Perhaps Authors meant ‘rpm’?

-          Line 341: it should be  ‘Available online’, not ’Availabie online’

Author Response

Comments and Suggestions for Authors:

In the reviewed article Authors discussed the current and extremely important problem of widespread environmental pollution by the (micro)plastics. Authors reviewed and discussed the newest research results concerning the possibilities of using microorganisms and the biochemical processes to degrade microplastics. The manuscript is well prepared, clearly written, quite comprehensive, relevant for the field, and presented in a well-structured manner. The cited references are mostly (over 75%) recent publications (within the last 5 years) and relevant to the field. The statements and conclusions drawn are coherent and supported by the listed citations and the presented figures and tables are appropriate and easy to understand.

While other similar literature reviews were published in the last two years, this review is most likely the first to include results of research of ‘coupled enhanced technologies’ – combination of physico-chemical and biological methods of microplastics degradation. Therefore, I believe that the current review is still relevant and of interest to the scientific community.

Response: We sincerely appreciate you for your time in reviewing the manuscript and giving your valuable comments. We have thoroughly considered your precious comments and suggestions, and carefully addressed every one of them as best as we can. Revisions in the manuscript were highlighted in red. Here, we provide a point-to-point response to your major and specific comments below.

 

However, there are still some things and sentences that require improvement:

• Line 29: perhaps word ‘significant’ instead of ‘vital’ would be better.

Response: Thank you very much for your valuable suggestions. In Line 29, ‘vital’ has been replaced by ‘significant’ according to your suggestions.

 

• Line 37: word ‘stability’ is not entirely understandable, perhaps word ‘longevity’ or ‘durability’ would be more correct.

Response: Thank you very much for your valuable suggestions. In Line 37, ‘stability’ has been replaced by ‘durability’ according to your suggestions.

 

• Table 2. What are ‘strokes/min’? Perhaps Authors meant ‘rpm’?

Response: Thank you very much for your valuable suggestions. The term ‘strokes/min’ refers to the linear reciprocating units of motion and was used in the original text of the reference we cited. Similar to ‘rpm’, the term ‘strokes/min’ is another unit of spin velocity. However, it is hard to directly convert these two units without detail information of the shaker-incubators applied in references. Therefore, the unit ‘strokes/min’ was used in Table 2 as it was depicted in reference [36].

 

• Line 167: citation [50] is incorrect.

Response: Thank you very much for your careful review of the manuscript. We have thoroughly checked the references of the full text. In Line 167, citation [50] has been revised according to your suggestions.

 

• Line 183: font used for Latin names is in different size than the rest of the line.

Response: Thank you very much for pointing out the problem. In Line 183, we have revised the font size of the Latin names.

 

• Lines 188-193: Latin names should be written in italics.

Response: Thank you very much for your careful review of the manuscript. We have checked the full text and all the Latin names have been written in italics.

 

• Table 4, lines 2 and 3, plastic weight loss data are missing; if they are not reported please add ‘not reported’ or ‘not available’.

Response: Thank you very much for your valuable suggestions. In Lines 2 and 3 of Table 4, we have added ‘not available’ according to your suggestions.

 

• Line 238: I am not certain that the name used in the subtitle is correct. Genetic engineering technology is not an augmentation technology. Perhaps the technologies presented in this subchapter could be named ‘Coupled enhanced technologies’?

Response: Thank you very much for your valuable suggestions. In Line 247, the subtitle has been replaced by ‘Coupled enhanced technologies’ according to your suggestions.

 

• Line 341: it should be ‘Available online’, not ‘Availabie online’

Response: Thank you very much for your careful review of the manuscript. In Line 350, ‘Availabie online’ has been revised to ‘Available online’.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The analysis of evolved CO₂ may be complemented by measuring the conversion of the plastic’s carbon into microbial biomass. For this purpose, the use of carbon isotope-labeled plastics is the best, if not the only valid option, as recently demonstrated. Many experimental observations that are not directly related to the microbial conversion of the plastic’s carbon, such as the visual disappearance of plastic, plastic mass loss, a decrease in the plastic’s tensile strength, or microbial growth, are ill-suited to assess plastic biodegradation. Unfortunately, such experimental data is often falsely used to assess the biodegradability of certain plastics. Following are some of my comments on this manuscript.

1.     The legend of Table 2 should be “Pure microbial degradation of (micro)plastics” since the table includes not only bacteria.

2.     Section 3.2.1, L. 183. “Tenebrio molitor” is apparently with a different font size.

3.     Section 3.2.2. The genus names of Bacillus and Pseudomonas should be italicized in the first paragraph.

4.     Section 3.2.2. The second and third rows of Table 4 do not show the plastic weight loss during the studies. How could these studies demonstrate the biodegradation of the plastics? The results could be briefly described in the text to support the statement.

5. This manuscript gives a broad review of the properties of plastics. However, plastic biodegradability is not only a material property but also largely depends on the properties of the receiving environment. It is better to describe how environmental factors impact plastic biodegradability to give a profound scientific background. The description of Section 3.3. is too superficial.

Comments for author File: Comments.pdf

Author Response

Comments and Suggestions for Authors:

The analysis of evolved CO₂ may be complemented by measuring the conversion of the plastic’s carbon into microbial biomass. For this purpose, the use of carbon isotope-labeled plastics is the best, if not the only valid option, as recently demonstrated. Many experimental observations that are not directly related to the microbial conversion of the plastic’s carbon, such as the visual disappearance of plastic, plastic mass loss, a decrease in the plastic’s tensile strength, or microbial growth, are ill-suited to assess plastic biodegradation. Unfortunately, such experimental data is often falsely used to assess the biodegradability of certain plastics. Following are some of my comments on this manuscript.

Response: The reviewer’s insightful suggestions on the biodegradation of microplastics are very much appreciated. Enlightened by your valuable suggestions, we have revised the manuscript and the revisions have been highlighted in red. To facilitate your further review, the contents are extracted as follows:

 

• The legend of Table 2 should be “Pure microbial degradation of (micro)plastics” since the table includes not only bacteria.

Response: Thank you very much for your valuable suggestions. In Line 173, We have revised the legend of Table 2 according to your suggestions.

 

• Section 3.2.1, L. 183. “Tenebrio molitor” is apparently with a different font size.

Response: Thank you very much for your careful review of the manuscript. We have checked the full text and revised the font size according to your suggestions.

 

• Section 3.2.2. The genus names of Bacillus and Pseudomonas should be italicized in the first paragraph.

Response: Thank you very much for pointing out the problem. We have checked the full text and all the genus names have been written in italics.

 

• Section 3.2.2. The second and third rows of Table 4 do not show the plastic weight loss during the studies. How could these studies demonstrate the biodegradation of the plastics? The results could be briefly described in the text to support the statement.

Response: Thank you very much for your valuable suggestions. In Section 3.2.2, we have supplemented the related results and discussions in the manuscript to support the statements.

 

• This manuscript gives a broad review of the properties of plastics. However, plastic biodegradability is not only a material property but also largely depends on the properties of the receiving environment. It is better to describe how environmental factors impact plastic biodegradability to give a profound scientific background. The description of Section 3.3. is too superficial.

Response: Thank you very much for raising this important point. Following your helpful suggestions, we have supplemented the contents on how environmental factors impact plastic biodegradability. The revisions have been highlighted in red in Section 3.3.

Author Response File: Author Response.pdf