Biofilm Structural and Functional Features on Microplastic Surfaces in Greenhouse Agricultural Soil

Round 1

Reviewer 1 Report

In this study, authors observed biofilm formation on microplastic particles incubated in greenhouse soil for 30 days.  Their work was very systematic and easy to follow and the results are clearly presented.  The manuscript meets the criteria for publication in this journal but it could be improved with some minor changes. 

 

Is this method for soil preparation new? If it's not please put a reference for it. 

Line 114- How much water did you add each time? 

Did you treat in the same way control MP just without soil? (incubation only in water at the same temp and daily cycles)

Line 132 reference missing for EDTA technique. 

Line 139 reference for this method 

In conclusion, the aim of this research should be written more clearly (line 348)

 

 

Author Response

Response to Reviewer 1 Comments

Point 1: Is this method for soil preparation new? If it's not please put a reference for it.

Response 1: We are very grateful for this question. The method of soil pretreatment in the manuscript is not new and I have added the reference (Line 140).

On [28], Hou, J.; Xu, X.; Yu, H.; Xi, B.; Tan, W. Comparing the long-term responses of soil microbial structures and diversities to polyethylene microplastics in different aggregate fractions. Environ. Int. 2021, 149, 106398.

 

Point 2: Line 114- How much water did you add each time?

Response 2: Thanks for your comments. I added the following sentence on line 140. “ Throughout the experiment, 150 ml of water was added daily.”

 

Point 3: Did you treat in the same way control MP just without soil? (incubation only in water at the same temp and daily cycles)

Response 3: We sincerely thank the reviewer for careful reading. In order to avoid the influence of MPs carried by MPs on the experiment, we use sterilized MPs as experimental materials. MP pretreatment is described. MPs were soaked in 75% ethanol and then disinfected using UV light (line 115).

 

Point 4: Line 132 reference missing for EDTA technique.

Response 4: We sincerely appreciate the valuable comments. We have added a reference to the EDTA technique in section 2.4 in the revised manuscript (Line 161).

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Point 5: Line 139 reference for this method

Response 5: We sincerely appreciate the valuable comments. We have added references to the observation of biofilms on MP surfaces using SEM in section 2.5 of the revised manuscript (Line 176).

On [33], Zhou Q, Zhang H, Fu C. The distribution and morphology of microplastics in coastal soils adjacent to the Bohai Sea and the Yellow Sea. Geoderma 2018, 322: 201-208.

 

Point 6: In conclusion, the aim of this research should be written more clearly (line 348)

Response 6: Thanks for your comments. We have added the aim of this research in the conclusion. “ The primary goal of this research was to determine how biofilms generated on the surface of MPs affect the environment of MPs and soil microbial populations in greenhouse agriculture. Meanwhile, there is a dynamic process of biofilm development on the surface of MPs with different species and concentrations in greenhouse agricultural soils.” (Line 405-410)

Author Response File: Author Response.pdf

Reviewer 2 Report

Dear Authors,

I have read Your manuscript entitled: "Biofilm structural and functional features on microplastic surfaces in greenhouse agricultural soil." Please find some guidelines:

1.       Avoid repeating words from the title as keywords. It can narrow the search area.

2.        In the Introduction section, the novelty and the research gap should be emphasized.

3.       Please add producer/supplier name, model, and country when providing equipment and reagents.

4.       Section 3.1: You describe only LDPE and PS; what about other plastics? Furthermore, You mention Figure 2, but in Figure 2, HDPE is presented, not LDPE.

5.       Please explain the samples' names, e.g., HDPE1, HDPE5? Is the name of samples duplicates? Maybe, in section 2.1, it should be described. Please, also provide information about the number of sample duplicates in the study.

 

6.       The results discussion should be expanded, i.e., in section 3.1, any comparison to others references can be found; in section 3.2, only one.

Author Response

Response to Reviewer 2 Comments

Point 1: Avoid repeating words from the title as keywords. It can narrow the search area.

Response 1: Thanks for your suggestion. I have changed the keywords in my manuscript into “ microplastics; biofilm formation; EPS ; biodegradation; microbial community composition”.

 

Point 2: In the Introduction section, the novelty and the research gap should be emphasized.

Response 2: Thanks for your comments. In the introduction section of the revised paper we added novelty of this study. “ Despite of the many studies carried out on MP biofilms in soil and microbial degradation of MPs, there has been little investigation about the greenhouse agricultural soil. The mechanisms of interaction between biofilm and MP degradation, as well as the environmental impacts and ecological aspects of biofilms, need further study. Furthermore, at varied exposure times, the dynamic effects of different kinds and concentrations of MPs on the overall quantity of biofilms and extracellular polymers remain unknown.”

 

Point 3: Please add producer/supplier name, model, and country when providing equipment and reagents.

Response 3: Thanks for your suggestion. The equipments' and reagents' detailed descriptions were given in sections 2.3, 2.5, and 2.6.

 

Point 4: Section 3.1: You describe only LDPE and PS; what about other plastics? Furthermore, You mention Figure 2, but in Figure 2, HDPE is presented, not LDPE.

Response 4: We sincerely thank the reviewer for careful reading. As suggested by the reviewer, we have corrected the “ LDPE” into “ HDPE” in section 3.1. There are two reasons for only LDPE and PS in my manuscript. The first is that HDPE and LDPE have similar surface characteristics and multi-texture architectures. PS, PP and PET also have similar structures, with smooth surfaces and less pore structure. The second reason is that biofilms enriched on HDPE and PS surfaces change significantly and representatively across all MPs with increasing exposure time. As a result, the major analytical objects were chosen to be HDPE and PS.

 

Point 5: Please explain the samples' names, e.g., HDPE1, HDPE5? Is the name of samples duplicates? Maybe, in section 2.1, it should be described. Please, also provide information about the number of sample duplicates in the study.

Response 5: Thanks for your comments. “ 1 ” and “ 5 ” indicate two concentrations (1% and 5% of soil dry weight), and here HDPE1 and HDPE5 represent 1% (w/w) HDPE and 5% (w/w) HDPE, respectively. The names of the MPs that appear in the experimental results have already been detailed in section 2.1. In this experiment, I set up 3 parallel experiments for each treatment, which appeared in section 2.2.

 

Point 6: The results discussion should be expanded, i.e., in section 3.1, any comparison to others references can be found; in section 3.2, only one.

Response 6: We sincerely appreciate the valuable comments. Four comparisons and references have been added to the revised manuscript. First of all, there are a variety of MP-degrading bacteria in soil (section 3.1). Secondly, the amount of biofilm on MPs grew dramatically over time. Thirdly, MPs' structural properties and hydrophilicity are affected by the resultant biofilm. Finally, mature biofilms differ from emerging biofilms (section 3.2).

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Author Response File: Author Response.pdf