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Evaluation of metabolism using stoichiometry in fermentative biohydrogen
Author(s) -
Lee HyungSool,
Rittmann Bruce E.
Publication year - 2008
Publication title -
biotechnology and bioengineering
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.136
H-Index - 189
eISSN - 1097-0290
pISSN - 0006-3592
DOI - 10.1002/bit.22107
Subject(s) - fermentation , chemistry , propionate , butyrate , biohydrogen , mixed acid fermentation , stoichiometry , yield (engineering) , metabolism , dark fermentation , biochemistry , bacteria , lactic acid fermentation , organic chemistry , hydrogen production , catalysis , lactic acid , biology , materials science , metallurgy , genetics
We first constructed full stoichiometry, including cell synthesis, for glucose mixed‐acid fermentation at different initial substrate concentrations (0.8–6 g‐glucose/L) and pH conditions (final pH 4.0–8.6), based on experimentally determined electron‐equivalent balances. The fermentative bioH 2 reactions had good electron closure (−9.8 to +12.7% for variations in glucose concentration and −3 to +2% for variations in pH), and C, H, and O errors were below 1%. From the stoichiometry, we computed the ATP yield based on known fermentation pathways. Glucose‐variation tests (final pH 4.2–5.1) gave a consistent fermentation pattern of acetate + butyrate + large H 2 , while pH significantly shifted the catabolic pattern: acetate + butyrate + large H 2 at final pH 4.0, acetate + ethanol + modest H 2 at final pH 6.8, and acetate + lactate + trivial H 2 at final pH 8.6. When lactate or propionate was a dominant soluble end product, the H 2 yield was very low, which is in agreement with the theory that reduced ferredoxin (Fd red ) formation is required for proton reduction to H 2 . Also consistent with this hypothesis is that high H 2 production correlated with a high ratio of butyrate to acetate. Biomass was not a dominant sink for electron equivalents in H 2 formation, but became significant (12%) for the lowest glucose concentration (i.e., the most oligotrophic condition). The fermenting bacteria conserved energy similarly at ∼3 mol ATP/mol glucose (except 0.8 g‐glucose/L, which had ∼3.5 mol ATP/mol glucose) over a wide range of H 2 production. The observed biomass yield did not correlate with ATP conservation; low observed biomass yields probably were caused by accelerated rates of decay or production of soluble microbial products. Biotechnol. Bioeng. 2009; 102: 749–758. © 2008 Wiley Periodicals, Inc.