Review Reports

Round 1

Reviewer 1 Report

The manuscript with the title:” Sulphate reducing bacteria response to pH extreme environments and the effect of their activities on microbial corrosion” is very well written and I accept this paper in the present form. This review presents important information about SRP strategies for survival and growth under extreme pH environment. Chapter 5, titled: Microbial corrosion by SRB deserves special attention.

The authors carefully studied the literature on this issue (136 references, 9 references from 2020, 7 references from 2019). I have found only two minor editorial mistakes (Row 583-the last sentence should be moved behind Table 1; Row 587- appeared twice - Table 1).

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Reviewer 2 Report

Thank you very much for the well-written review. I enjoyed reading about the topic, with a fresh light on SRB corrosion and also the putative protective effect of biofilms. Please find my major and minor comments below. Mostly this concerns the bioenergetics with regard to sulphide reduction according to the sulphide equilibrium and some microbiological/biochemical expression issues e.g., ATPases. English proofreading is also necessary, as often singular and plural were mixed up. Some examples are mentioned below.

 

Line 2: Sulphate reducing bacteria respond...

Line 19: … SRB have developed…

Line 39: ...growth rate of bacterial….

Line 49: … for a long time ….

Line 58: remove space

Line 89: remove Its, capitalise the, correct lower case Sulphate

Line 102: remove space

Line 118/119: remove spaces

Line 120: consider replacing bacteria by SRB or the specific genus and species

Line 122: remove bacterial

Line 138: this sentence makes no sense: go through bacteria cytoplasm via plasma membrane, do you mean into the cytoplasm?

Line 145: a proton is always positively charged, remove the tautology

Line 147 to 149: check grammar and writing, please strongly consider using the same wording/expressions as in lines 138 to 141.

Lines 150/151: Biologically, the cytoplasmic membrane … Not all biological membranes are bilayer membranes

Lines 151 to 153: remove: membrane contains channel protein which is a special arrangement of amino acids embedded in the cell membrane to allow the influx of protons and nutrients and extrusion of waste products [32]. Hence, the

Line 155: ….bacterial membrane….

Line 163: Amaro et al. …

Line 172: are you sure you mean ATP hydrolysis? Or do you mean ADP phosphoylation by proton-dependent ATPases? Or both?

Line 173/174: Remove: The presence of enzyme F 1 F 0 -ATPase is reported to improve the proton pump out of the cytoplasm. This is general knowledge and one of the two functions of an ATPase

Line 176: remove bacteria after Enterococci as they are bacteria

Line 186: remove SRB

Line 187: remove space

Line 188: remove bacteria

Line 191: literature

Line 231: remove space

Line 246: Fortin et al. …

Lines 286 to 271: Please order the equations accoring to pH starting with the most neutral pH equations as equation 1.

Lines 273/274: Comment: you mean that the reaction becomes more exergonic? So the value for the gibbs free energy becomes more negative (standard conditions?) What I don‘t understand here is the S2-/HS-/H2S equilibrium with regard to the bioenergetics of the reaction. With an equilibrium to the right side (for H2S) at low pH, can you explain how the reaction is more exergonic? Is it solely due to the proton concentration? I was under the impression that H2S is the preferred product of the reaction (right side of the equation). Please provide bioenergetic calculations according to the standard conditions and also according to the assumed intracellular pH. Maybe you add the Gibbs free energy of the reactions to equaitons 1 to 4. Please consider here also the resoning you provide in lines 289 to 300 as well as the chapters 4.2.1 (lines 455 to 457) and 4.2.2, and lines 643/644

Line 287: Reis et al. …

Line 308: Habitats …

Line 309: literature

Lines 310/312: correct as follows: Survival and growth of D. vulgaris ATCC 7757 [18] and non-alkaliphilic SRB consortia [72] were discovered.

Line 341: Sergey et al. …

Line 343: is OR was exposed

Line 346: … uses…

Line 350: KD is actually not used in microbiology/biochemistry. We refer to is as KM or KS value. KM for proteins, KS for cells (with a subscript M or S, respectively)

Lines 349 to 358: The ATPase produces ATP insinde the cell and would require an acidic pH outside to be engaged in proton dependent ATP production or are you referreing to Na dependent ATPases? I am not sure if SRB would harbour these type of ATPases.

Line 362: gene …

Line 368: D. italicize

Line 373: D. Vulgaris italicize

Line 381: literature

Line 387: NH3, subscript 3

Line 402: D. Vulgaris, italicize

Line 413: Coo hydrogenase? CODH? CO? Co? Carbon monoxide dehydrogenase, carbon monoxide, OR copper?

Line 422: D. vulgaris, italicize

Line 462: ….bacterium…

Lines 437/438: however they resume to grow after few days when environmental pH decreases [18]. Comment: did D. vulgaris alter the pH of the medium or why did the pH in the medium drop? Please mention that.

Line 459: Environmental condition contains high carbon sources. What do you mean exactly here? This is not necessarily true. Specify.

Line 474: … research …

Line 519: of passive, space

Line 540: reference is missing, as you make a statement, which is referring to a proof.

Line 545: … environments [106-108]. Chongdar et al. ...

Line 549: Rongjun et al.

Line 550: alloy Al 2024, space?

Line 556: it is strange to this reviewer to start with a: However, . Moreover this reviewer suggests to remove lines 556 to line 567 starting the text again with: the presence of biofilm matrix, as these are too many details of the paper you refer to. A 7 words summary of the paper /ref 17/ would also do it.

Line 606: water. Further, space?

Line 616: Tang et al.

Line 610 to line 641, chapter 5.2.1. this paragraph is not related to microbial activity. Please remove or shorten to an one sentence/two sentences summary.

Line 660: μm. year -1, remove full stop twice in units

Line 670: literature…

Line 676: on the other hand, …

Line 677: D. vulgaris, italicize

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Reviewer 3 Report

Dear Authors,

The review manuscript entitled “Sulphate reducing bacteria response to pH extreme environments and the effect of their activities on microbial corrosion” is of interest for the readers and fits to the scope of the journal. There exist a lot of Reviews on SRB and MIC, but only few studies consider the pH of the environment. The manuscript is written straight forward except of 3. This part can be optimized. Some minor points are:

Line 19: has has to be replaced by have

Line 52 to 58: This part sounds not very good. It is just a sequence of sentences. Please rewrite this passage.

Line 58: delete one “space” after “grow”.

Figure1: script of the Figure is not readable, it is blurred.

Line 101: delete the “space” after “oxidized”.  

Line 106: H₂ is not a product of SRB, it is a product of SRB metabolic activity

Line 114 to 123: This part is not written very carefully written. It is a only a sequence of sentences. This part should be rewritten.

Line 252: It seems as the authors do not really know what is meant by “biofilm” and how it is formed.  SRB cannot be “protected by a matrix of minerals and biofilm”. Maybe the authors want to say that the matrix of a biofilm in which can be inhabited by SRB, can protect them. The biofilm itself is defined as microorganisms embedded in a matrix of EPS. Furthermore, biofilms are not caused by precipitation of sulphide and iron/other metals. Biofilm formation is caused by AHLs e.g. and metals can be incorporated into the EPS.  Please clarify this sentence.

Figure 2: same as for Fig 1. Script is not readable.

Lie 492: “space” after MIC should be deleted.

Line 571: rewrite this sentence “the matrix of biofilm and precipitation of corrosion products”. Biofilm means bacteria or microorganisms embedded in a matrix and the matrix can also include precipitated corrosion products.

Line 677: D. vulgaris should be written in italic letters.

Line 691 to 701: H2S has to be changed to H₂S in this paragraph.

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Reviewer 4 Report

The manuscript tries to fill the knowledge gap on how SRB response to environmental extreme acidic and alkaline pH. In addition, corrosion by SRB is also discussed. This review has 136 references, and is nicely written .  One of my concern is "the manuscript ends abruptly, and did not discuss the critical evaluation of cited references.  Authors could make few suggestions for the readers. Figures 1 and 2 are also vague, and should be improved.  What is new in Figure 1?  Also what genes are down regulating in Figure 2 (I don't see any), it need more details.

Minor comments:

Page 2, line 89: -516 mV does not sound right.  Please check.  Line 93-94: what is trisulphide here?  Is it sulfite?

Page 3, Line 106-111 - Need reference/s.

Line 126-128: Need reference/s.

Line 179-182: Need reference/s.

Line 349-353: Need reference/s.

Line 533-539: Need reference/s.

D. vulgaris has not been italicized at several places in the manuscript text.  Please check.

Page 5, Line 214: change gram to Gram

Page 11, Line 493: Are you sure "Hydrogen" as electron acceptor?  

 

  

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Round 2

Reviewer 3 Report

Dear Authors, comments have been considered, however figures are still in bad quality.

Author Response

 

Thank you for your constructive comments. We tried to make the figures clearer last time, but it did not work well so this time, we have redrawn both figures to make it clearer to the readers.