pH-Dependent Metabolic Regulation in Clostridium ljungdahlii During CO Fermentation

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This study explores the pH-dependent regulation of growth and ethanol production in Clostridium ljungdahlii using CO as the sole carbon source. They investigated fermentation profiles of various pHs of media of C. ljungdhahlii, and found that at pH 5.3, the bacterium exhibited significantly enhanced metabolic activity, consuming more carbon monoxide and producing higher levels of ethanol, acetate, 2,3-butanediol, and lactate compared to pH 6.0. Proteomic analyses indicated that these enhancements were not due to differential enzyme expression but likely resulted from variations in ATP synthesis efficiency. The optimal pH for growth and ethanol production was found to be approximately 5.3.

 

 

The research is well performed and significant results are obtained.

 

However, the manuscript lacks clarity and detailed information.

 

Figs need fig legends and explanations. It is not clear which is the obtained results. Tables need explanations.

 

Experimental procedures need detailed descriptions/ which machine or program was used for carbon and energy flux analysis? What was the experimental condition for proteomic analysis? And so on

 

Fig5 where are (A) and (B)?

 

P9 interpretation of proteomic analysis should be described.

 

Fig6 characters are invisible.　

Author Response

see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

Dear Authors,

 

I reviewed your highly intriguing manuscript, which studies the effect of cultivation pH-value on formation of the biofuel ethanol and other bioproducts (2,3-butanediole, lactate, acetate) by cultivation of Clostridium ljungdahlii on CO as the sole carbon- and energy source. It was shown that a pH-value of around 5.3 is more efficient for ethanol and biomass production than the established pH-value 6.0. proteomic and parallel reaction monitoring modelling were carried out to determine expression levels of enzymes involved in the strain´s metabolism. Due to the fact that no tremendous differences in key enzyme expression levels were monitored, it was concluded that the enhanced metabolic performance originates from higher ATP synthesis efficiency.

The work is scientifically sound, the conclusions are well substantiated by the elaborated experimental and modelling data. The experiments are well planned and described. The work is also of practical interest for enhanced ethanol production from syngas.

Some minor aspects should be addressed to further improve the manuscript:

1. Line 77, 78, 84: species name should be in italics.
2. Line 111: what was the total volume of the bioreactor used? Only the working volume (2.5 L) is disclosed.
3. Line 116: what are “concentration nutrients”?
4. Line 259: “pH 5.3 condition “: remove “condition”
5. Section 3.4: Optimal pH for the growth and metabolism in CO fermentation: were these experiments carried out in flasks or in bioreactors?

Author Response

see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

Required revisions have been added.