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ATP and average stoichiometric numbers


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I apologize for my poor English in advance.

I have some questions about χ and m values in the kinetic of microbial reaction of React software. I am referring to the two articles to understand the logic of the input values, which are Jin and Bethke, 2005 and Bethke et al, 2011.

Article1. Jin and Bethke (2005) Geochimica et Cosmochimica Acta Vol. 69(5) pp. 1133-1143.

Article2. Bethke et al. (2011) American Journal of Science Vol. 311 pp.183-210.



In the case of SO4 reduction consuming H2, the article1 used (m, χ) = (1/3, 2), and the article2 used (1, 6), respectively. If the article2 considered four H2 (p. 188 and p. 192), I thought that (m, χ) = (4/3, 8) should be adopted based on the values of the article2 which considered one H2 (p. 1136). Could you help me understand the logic of that? Instead of four times, why does it three times?



I could not lead same values as Table 3 of the article2 using Table 1 and the information written in the section of 3.2. Thermodynamic Parameters of the article1 in each of microbial reactions. Why was the m value in methanogenesis 1/4 not 2/9? How about other reactions?


I’m looking forward to hearing from you.


Best regards,



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Hi Maki,


Regarding question 1, I think I agree with some of your logic. In the 2005 paper, m and X for hydrogentrophic sulfate reduction (m = 1/3, X = 2) are written in terms of 1 H2 (or 2 e-, or 1/4 SO4--). If the reaction is written in terms of 4 H2 (or 8 e-, or 1 SO4--), then I think the m and X values would be 4/3 and 8, respectively. Without looking into either reference too closely I can't say why the 2011 paper (written in terms of 8 e-) has slightly different values for m and X (m = 1, X = 6).


It looks like the values assumed for the methanogens are slightly different as well. Perhaps the physiology described is slightly different? I think you should take note of the relative values for m and X corresponding to the various functional groups (iron reducers, sulfate reducers, and methanogens) in the 2011 paper.


Since this is an area of active research, I might go with the more recent paper's values. You might also search out more references by Qusheng Jin. I believe he has a new paper which describes some more of this material in detail .




Brian Farrell

Aqueous Solutions LLC

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