Comparison of Bacterial Community Structure in PM2.5 within Broiler Houses under Different Rearing Systems in China

Round 1

Reviewer 1 Report

Review of the manuscript (sustainability-1440785) entitled “Comparison of Bacterial Community Structure in PM2.5 within  Broiler Houses under Different Rearing System in China”

 

The manuscript deals with an interesting topic that could be of interest to the readers of Sustainability. However, it needs to undergo some modifications/clarifications. 

 

1.- The manuscript focus on PM2.5. The authors do not indicate clearly and consistently why they consider only PM2.5. Why not PM10 or PM1?

2.- In the same vein, some of the analytical choices made by the author need to be justified. For instance, why did you use LSD ANOVA?  

3.- The result and/or the discussion sections need to be refined. In its current form, the authors present the results and indicate that they are consistent with some published papers. However, the reader may wonder why the authors did not provide explanations for their results. For instance, on Page 6 (lines 193-194) “There was no significant difference in any of the ion concentrations between CH and FH groups”; How could you explain this result? Why there is no difference? Note that this is an example, but all the results need to be explained.

4.- Figure 2: Information presented on the horizontal axis should be defined to facilitate the reading of the manuscript.

5.- A thorough proofreading is needed. For instance, on Page 2 (line 63) you write “andFH”. 

Author Response

We would like to express our sincere thanks to the reviewers for the constructive and positive comments. We have studied the comments carefully and made corrections which we hope meet with approval.

 

Comment 1. The manuscript focus on PM2.5. The authors do not indicate clearly and consistently why they consider only PM2.5. Why not PM10 or PM1?

Response:

To indicate clearly that the manuscript focus on PM2.5, we have replaced the sentence “High concentration…” in L37-40 by “Their toxicity is increased with smaller size, larger surface area and adsorbed surface material of the particles. The 2.5–10 μm PM (PM10) are partially traped by nasopharynx, but the fine particulate matter less than 2.5 μm in (PM2.5) can enter the deep part of the respiratory tract and mainly deposit in the bronchi and lungs.”

And in L43, add one more explanation “The sizes of aerosol bacterial cells were reported to be ranged from 1.1 to 2.1 μm and from 2.1 to 3.3 μm, respectively [3].”

 

2. In the same vein, some of the analytical choices made by the author need to be justified. For instance, why did you use LSD ANOVA?

Response:

We have revised the statistical analysis part to explanations of the statistical methods chosen, and added relevant references. The revised statistical analysis part:

“Alpha diversity indices of Chao 1 and Shannon were estimated. QIIME software was used to calculate the beta diversity distance matrix. Correlations between bacterial com-munity and environmental control variables were performed using a linear mode of re-dundancy analysis (RDA) with Canoco 4.5.

The experimental results are shown as the mean ± standard error of mean (SEM). The data were statistically analysed using GraphPad Prism 6.0 software. Least-Significant Difference (LSD) one-way analysis of variance (ANOVA) was carried out to examine sig-nificant differences between the 3 different rearing stages settings. An independent sample t-test analysis was used to compare the mean concentrations of PM2.5 in CH and FH. Spearman's rank correlation analysis was then used to examine correlations between water-soluble ions and airborne bacteria. The analyses were performed in an IBM SPSS Statistics 24.0 (SPSS, Inc., Chicago, IL, USA) for Windows, and a P-value <0.05 was considered statistically significant difference at a confidence level of 95%.”

 

3. The result and/or the discussion sections need to be refined. In its current form, the authors present the results and indicate that they are consistent with some published papers. However, the reader may wonder why the authors did not provide explanations for their results. For instance, on Page 6 (lines 193-194) “There was no significant difference in any of the ion concentrations between CH and FH groups”; How could you explain this result? Why there is no difference? Note that this is an example, but all the results need to be explained.

Response:

Modifications have been done in the result section, and explanations have been added in the discussion section, as the reviewer’s comments.

4. Figure 2: Information presented on the horizontal axis should be defined to facilitate the reading of the manuscript.

Response:

We have added the definition of figure 2 as “The rearing stages were illustrated with D10 (day age 10), D24 (day age 24) and D38 (day age 38), respectively.”

 

5. A thorough proofreading is needed. For instance, on Page 2 (line 63) you write “andFH”. 

Response:

We are very sorry for our negligence. Comprehensive inspection and modification have been done carefully.

Author Response File: Author Response.pdf

Reviewer 2 Report

This manuscript reports a comparison of bacterial community structures in PM2.5 under different house rearing systems, specifically the multilayer cage house (CH) vs the net flooring house (FH). The poultry farming is an important unit in many countryside areas in China and play important roles in the indoor air pollution and somehow contribute to outside ambient air pollution as well. The results show that the CH is advantageous over the FH in terms of pollution control on the PM and trace gases. The topic seems to be interesting and worthy of investigating. The manuscript is well prepared; however, some issues need to be resolved.

1. Why the water-soluble ion concentration was in unit of mg/g, instead of mg (or ug) per m^3, as used by the PM concentration? Some comparisons might need to be revised when using the suggested unit.
2. Why the concentrations of sulfate, ammonia, nitrate in CH are much higher than those in FH? The ammonia concentration and the mass concentration of PM in Fig. 2 show the opposite trend.
3. The PM and trace gas concentrations under the two house conditions might also heavily depend on the control measures such as ventilation, cleaning frequency, etc. Give some more discussion on those factors.
4. Some minor comments:

• Figure 2 can be improved, in particular, the symbols in A-D are not clearly distinguished from one to another.
• Some words are capitalized in the middle of sentences which should not be, e.g., P5, line 11 from bottom, “Both the CO2…”
• How average concentration of PM2.5 was calculated in Fig. 2?
• Please show the detection limit of the instruments for trace gas measurements.
• A lot of typos when stating “shown” instead of using “showed”, please doublecheck.
• Where is Table 1???
• Line 8 from bottom on p.6, should it be “Fig. 3”?
• L200 on p.7, “There were 1775 Operational 200 OTUs was clustered at 97% similarity level …”, ill sentence.
• L258 on p.10, “were clustered”
• L295-297 on p.11, “…higher … than the house.”
• L312 on p.11, ill sentence, L314, similar to not with.
• L326 on p.11, delete seemingly
• L371-372, ill sentence, please revise.

 

Author Response

We would like to express our sincere thanks to the reviewers for the constructive and positive comments. We have studied the comments carefully and made corrections which we hope meet with approval.

1. Why the water-soluble ion concentration was in unit of mg/g, instead of mg (or ug) per m^3, as used by the PM concentration? Some comparisons might need to be revised when using the suggested unit.

Response: We are grateful to the reviewer for the comments. Actually, many study used the unit of mg/m3 to measure ion concentrations, especially in atmosphere researches. It reflects the quantity of ions in a unit volume of aerosol. But in animal confinement buildings, the PM concentrations have a distinct difference under different conditions sometimes. Just like in our experiment, the FH PM2.5 level was about 3-4 times more than CH in middle and late stages. The comparisons results will be greatly influenced by PM2.5 concentration in using unit of mg/m3. The unit of mg/g focuses on describing the mass fraction of ions in particles. We insist that unit of mg/g can better reflect the influence of ion composition on bacterial community. We have made modifications in result and discussion section and added one more reference [43] to clarify it.

2. Why the concentrations of sulfate, ammonia, nitrate in CH are much higher than those in FH? The ammonia concentration and the mass concentration of PM in Fig. 2 show the opposite trend.

Response: Thanks to the reviewers for their thought-provoking questions and suggestions. We refined the discussion as the comments. “Chemical analysis of PM showed that the total mass fraction of identified inorganic species was not the majority part (normally less than 16%), but the organic composition was [7,44]. And the composition varied significantly with animal building type [44]. There might not be enough difference between CH and FH, or the changes of organic and microbe composition alters the ion fraction. We found that the concentrations of SO42-, NH4+ and NO3- in CH were higher than those in FH but not significant.”

3. The PM and trace gas concentrations under the two house conditions might also heavily depend on the control measures such as ventilation, cleaning frequency, etc. Give some more discussion on those factors.

Response: We have revised the discussion and conclusion section. More discussion have been added.

4. Some minor comments:

• Figure 2 can be improved, in particular, the symbols in A-D are not clearly distinguished from one to another.

• Some words are capitalized in the middle of sentences which should not be, e.g., P5, line 11 from bottom, “Both the CO2…”

• How average concentration of PM2.5 was calculated in Fig. 2?

• Please show the detection limit of the instruments for trace gas measurements.

• A lot of typos when stating “shown” instead of using “showed”, please doublecheck. • Where is Table 1???

• Line 8 from bottom on p.6, should it be “Fig. 3”?

• L200 on p.7, “There were 1775 Operational 200 OTUs was clustered at 97% similarity level …”, ill sentence.

• L258 on p.10, “were clustered”

• L295-297 on p.11, “…higher … than the house.”

• L312 on p.11, ill sentence, L314, similar to not with.

• L326 on p.11, delete seemingly • L371-372, ill sentence, please revise.

Response:

 Figure 2 have been improved as the reviewer’s comments.

 The capitalized words in the middle of sentences have been checked and revised.  The average concentration of PM2.5 was calculated by three sampling positions (1.front, 2.middle, and 3. rear from the wet pad), showed in Fig1 c.

 The information of the instruments for trace gas measurements have been added as “Portable gas detectors (Qingdao, China, LOBO Company, LB-MS4X Model) were used to detect the contents of CO2 and NH3. The detection accuracy was 1ppm and 0.01ppm, respectively.”

 We are extremely sorry for the text error and would like to express our gratitude to the reviewer. The mislabeling, typos and ill sentences have been checked and revised carefully.

Author Response File: Author Response.pdf