Uncovering Hidden Microbial Diversity in Nitrate/Iodide Deposits (NIDs) in the Domeyko District, Atacama Desert, Chile

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The data presented in the manuscript are of great interest to all microbiologists who study microbial activity in extreme habitats. These data are also of interest to astrobiologists who study the possibility of the existence of microorganisms in extraterrestrial ecosystems.

The importance of the hygroscopic properties of minerals for maintaining microbial activity is an important finding of the authors of the work.

The manuscript is generally well organized and contains informative illustrations.

The points that require corrections are the following:

1. Abstract, Line 33 – one of the aims of the manuscript is to “provides new insights on…potential biosignatures”. What are the biosignatures? They should be discussed more clearly in the conclusion.

P.2, Lines 71-73 – «…facilitate the existence and diversity of microbial life and microbial nitrate/perchlorate reduction». It is formulated somewhat incorrectly...it may directly facilitate the existence of life, but only indirectly facilitate diversity and the process of reduction.

3. Materials and Methods, Results and Discuss – In these paragraphs, section numbering is incorrect. The section 1.1 follows the paragraph 2   and so on. The authors should check numbering all over the text.

4. P. 3, Line 97 - Please specify how the samples were homogenized? By means of which device?

5. Section 1.5 Enrichment cultures of nitrate/perchlorate reducing bacteria - Why was this particular medium and this temperature chosen for the enrichment? Could more indigenous microorganisms be isolated if the medium similar in mineral composition to that in sampling site would be taken and incubated at temperature close to its in situ meanings?

6. P.5, Line 179-182 – Unclear formulated. “…the large amounts of nitrate are not directly bioavailable to microbial life in Atacama since the global nitrogen cycle is inoperative due to the lack of denitrifying bacteria to convert nitrate into atmospheric nitrogen followed by nitrogen fixation at the biosphere”

If the nitrogen becomes available due to its cycle including denitrification and its release into atmosphere then its atmospheric pool should be sufficient to proceed the cycling further. What is the main process responsible for nitrogen availability? Please clarify!

Author Response

Dear reviewer, we appreciate the time you have dedicated to this review. We have carefully considered all of your suggestions, which are detailed below:

The points that require corrections are the following:

1. Abstract, Line 33 – one of the aims of the manuscript is to “provides new insights on…potential biosignatures”. What are the biosignatures? They should be discussed more clearly in the conclusion.

Dear reviewer, thank you for your feedback. Biosignatures are any substance or phenomenon that provides evidence for the existence of life; however, we have realized that it is better to edit the final conclusion of the abstract to avoid confusion. The revised final part reads as follows: "This study sheds light on the resilience of microbial life in the Atacama Desert NID, providing compelling evidence for its existence and offering insight into factors that could facilitate it within this unique environment."

P.2, Lines 71-73 – «…facilitate the existence and diversity of microbial life and microbial nitrate/perchlorate reduction». It is formulated somewhat incorrectly...it may directly facilitate the existence of life, but only indirectly facilitate diversity and the process of reduction.

Thanks for the comment, we have redrafted the phrase to avoid confusion: “This work aims to demonstrate that the hygroscopic capability of halite and the presence of nitrate salts at Atacama NID from the Domeyko District facilitates the existence of microbial life under the prevailing extreme environmental conditions”

3. Materials and Methods, Results and Discuss – In these paragraphs, section numbering is incorrect. The section 1.1 follows the paragraph 2   and so on. The authors should check numbering all over the text.

Thank you for your thorough review; we have carefully revisited the numbering in the text.

 

4. P. 3, Line 97 - Please specify how the samples were homogenized? By means of which device?

Thanks for the comment, we established in the text the method to homogenize and obtain representative samples.

5. Section 1.5 Enrichment cultures of nitrate/perchlorate reducing bacteria - Why was this particular medium and this temperature chosen for the enrichment? Could more indigenous microorganisms be isolated if the medium similar in mineral composition to that in sampling site would be taken and incubated at temperature close to its in situ meanings?

Thank you for your comment. This medium was chosen because it is specific for the enrichment of this type of microorganisms and it is a culture medium already tested by many authors. However, according to their comments, tests were carried out with two concentrations of nitrate and perchlorate according to what we found at the sampling site without changing the temperatures. However, we believe that the growth of more microorganisms native to the site will always be affected by the source of organic matter that they can obtain to enrich themselves, therefore it is possible that by changing the temperature and mineral concentration conditions, the growth of one of the two types of reducing bacteria is inhibited and therefore the microbial diversity may have been lower. Unfortunately, in this study we did not perform the tests suggested by the reviewer.

6. P.5, Line 179-182 – Unclear formulated. “…the large amounts of nitrate are not directly bioavailable to microbial life in Atacama since the global nitrogen cycle is inoperative due to the lack of denitrifying bacteria to convert nitrate into atmospheric nitrogen followed by nitrogen fixation at the biosphere”

If the nitrogen becomes available due to its cycle including denitrification and its release into atmosphere then its atmospheric pool should be sufficient to proceed the cycling further. What is the main process responsible for nitrogen availability? Please clarify!

Thank you very much for your detailed review. We rephrase for greater clarity including the two comments.

“Nitrogen transformation through decomposition and mineralization is carried on by soil microorganisms, although in arid land environments, optimal temperature and soil moisture growing conditions are not always present, only after rainfall pulses. Nitrogen mineralization in arid and semi-arid ecosystems are highly heterogeneous throughout the landscape and occurs in patches or fertility islands, because of their unique microclimatic, richness and abundance of plants, as well as nitrogen content in their soil”.

Reviewer 2 Report

Comments and Suggestions for Authors

The manuscript entitled “Uncovering Hidden Microbial Diversity in Nitrate/Iodide Deposits (NID) of the Domeyko District, Atacama Desert, Chile” describes the unique nitrate/iodine deposits microflora at the Atacama Desert. The obtained results are reliable, clearly presented and interesting for readers. The manuscript delivers a lot of interesting data about microbial life in extreme environmental conditions and their dependence on biogeochemical factors. The manuscript is scientifically sound. Ethical issues do not rise concern.

Minor remarks:

Line 254 “DNA was successfully extracted from only ten NID soil samples (Fig. 3).” Fig 3 refers to taxon biodiversity.

 

Lines 257 – 258 “… considering all samples (n=10) (Fig. 3)”. Fig 3 refers to taxon biodiversity. 

Author Response

Dear reviewer, we appreciate the time you have dedicated to this review. We have carefully considered all of your suggestions, which are detailed below:

Line 254 “DNA was successfully extracted from only ten NID soil samples (Fig. 3).” Fig 3 refers to taxon biodiversity.

Thanks for the detail, we have edited the sentence to make it clear.

Lines 257 – 258 “… considering all samples (n=10) (Fig. 3)”. Fig 3 refers to taxon biodiversity. 

Thanks for the detail, we have edited the sentence to make it clear.

Additionally, we have edited the grammar of the article for better comprehension.

Reviewer 3 Report

Comments and Suggestions for Authors

This is a well-organized manuscript, mainly dealing with microbial biodiversity in Nitrate and Iodine deposits located in North Chile, namely the Atacama Desert, which are worldwide unique. The results obtained show that “salt deliquescence provide liquid water to a diversity of bacterial genera with dominance of phyla Firmicutes and Proteobacteria” and a impressive microbial diversity. The paper does contribute to new insights about life under the extreme environmental conditions.

MAIN CONCERN

Authors also tried, however, to extrapolate the obtained results in Atacama to Mars planet conditions and in my opinion this position has not been demonstrated along the manuscript and may be exaggerated or flawed.

Please, consider to state in the Introduction the state of the art of knowledge about the geological deposits in Mars, which you consider similar to those found in Atacama. Also information about similitudes and differences of environments in Atacama and Mars (temperature, rainfall, even sporadic, etc.) is needed. Please, also provide references.

Please, be more consistent with the comparisons between Atacama and Mars in Abstract, Discussion and Conclusions.

 

 

OTHER COMMENTS

Please, carefully revise the References section, following the Instructions for Authors published by Sustainability. This is because several mistakes have been detected in this section. Next, I’m providing several examples, but this list is not exhaustive.

Reference 3, Line 432. 1994 appears two times.

Reference 9, Line 447. 1996 should be in bold

Reference 13, Line 457. 2022 should be in bold. In addition, please, add pages.

………….Etc., etc.,…

Refeence 47, Line 541. Title, journal, pages, etc., should be added,

………….Etc., etc.,…

Comments on the Quality of English Language

 

The English language needs carefully editing. Many sentences are to long and frequently difficult to understand.

There are also several redundancies and therefore incorrect sentences. For example, Line 328, shows or provides?

Typing errors along the text, including citations. For example, Line 378, should be 15, 62,65 and not 15.62-65 (into square brackets)

Author Response

Dear reviewer, we appreciate the time you have dedicated to this review. We have carefully considered all of your suggestions, which are detailed below:

Authors also tried, however, to extrapolate the obtained results in Atacama to Mars planet conditions and in my opinion this position has not been demonstrated along the manuscript and may be exaggerated or flawed.

Please, consider to state in the Introduction the state of the art of knowledge about the geological deposits in Mars, which you consider similar to those found in Atacama. Also information about similitudes and differences of environments in Atacama and Mars (temperature, rainfall, even sporadic, etc.) is needed. Please, also provide references.

Please, be more consistent with the comparisons between Atacama and Mars in Abstract, Discussion and Conclusions.

Thank you for your valuable feedback on our manuscript. We appreciate your suggestions and have taken them into account to improve the quality and clarity of our work. To address your concerns, we enhance the manuscript by providing an overview of the geological deposits on Mars and how they may relate to those found in the Atacama Desert. We discuss and conclude about the geological findings in the NID and the potential implications for Mars. This includes references the similarities and differences in environmental conditions and how they might impact our extrapolations.

Thank you for your insightful comments, which will undoubtedly enhance the scientific value of our research.

 

OTHER COMMENTS

Please, carefully revise the References section, following the Instructions for Authors published by Sustainability. This is because several mistakes have been detected in this section. Next, I’m providing several examples, but this list is not exhaustive.

Thanks for the detailed review, we have edited all the following questions

Reference 3, Line 432. 1994 appears two times. Edited

Reference 9, Line 447. 1996 should be in bold. Edited

Reference 13, Line 457. 2022 should be in bold. In addition, please, add pages. Edited

………….Etc., etc.,…

Refeence 47, Line 541. Title, journal, pages, etc., should be added, Edited.

………….Etc., etc.,…

Comments on the Quality of English Language

The English language needs carefully editing. Many sentences are to long and frequently difficult to understand.

There are also several redundancies and therefore incorrect sentences. For example, Line 328, shows or provides?

Typing errors along the text, including citations. For example, Line 378, should be 15, 62,65 and not 15.62-65 (into square brackets)

Thank you very much for your comment. We apologize for the errors, for which we have edited the grammar.

Round 2

Reviewer 3 Report

Comments and Suggestions for Authors

This manuscript has been ameliorated and my suggestions, regarding the soundness of comparison between soils or surface formations in Atacama Desert in Chile and Mars planet, have been taken into account. This notwithstanding I would like to encourage authors to further improve tis work taking into account the following additional comments.

Objectives and conclusions should be associated, and this is not the case in this manuscript. Please, try to enhance this issue. For example, comparison of Mars ad Atacama Desert is not considered as an objective in the present version of the paepr.

 

Lines 119 to 122. This sentence at the end of the Introduction isn’t an objective. Belongs this sentence to Conclusions or to other different section?

Lines 535 to 537. This sentence doesn’t belong to conclusion. It isn´t a new finding. Please delete or change to other different section.

Comments on the Quality of English Language

English Language has been tightened up. Quality of this version is much better than before.

Author Response

Dear Reviewer,

 

Thank you very much for your recent revision. We have addressed your concern by removing speculations related to Mars from both the objectives and conclusions while retaining relevant discussions tied to our specific findings and their relationship with Mars. Specifically, in the final part of the introduction, we eliminated the last paragraph and rephrased the objective of the paper for clarity. It now reads as follows:

 

"This study aims to investigate microbial life within nitrogen/iodide deposits in the arid core of the Atacama Desert. Specific objectives include assessing the presence, abundance, and diversity of microorganisms using metagenomic and culturing techniques, and examining their relationship with the physicochemical characteristics of the samples, such as mineralogical composition and water activity."

 

Regarding the conclusions, we also considered your feedback and have made improvements accordingly.

 

We appreciate your time and feedback.