Biological hydrogen production has received much attention and it is of practical interest to produce H2 biologically using low-cost lignocellulose-derived mix substrates, usually containing various compounds, such as...
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Biological hydrogen production has received much attention and it is of practical interest to produce H2 biologically using low-cost lignocellulose-derived mix substrates, usually containing various compounds, such as arabinose, formate, acetate, furfural, HMF, in addition to glucose and xylose. Herein, we systematically evaluated impacts of single/mixed model compounds, and energy sorghum hydrolysate on H2 production by Rhodobacter sphaeroides. We found (i) obvious cell growth was observed for all single substrates including formate, furfural and HMF, which for the first time, were reported in R. sphaeroides;(ii) cultures pairing acetate with a mixture of glucose and xylose remarkably improved H2 production compared to that without acetate;(iii) arabinose/ formate had limited effects on the mixed-sugar photo-fermentation;(iv) furfural/HMF degradation was expedited by co-utilization with glucose and xylose. The results support the conclusion that photo-fermentation with hydrolysate achieved comparable, or even advantageous H2 production over that of model compound mixtures. Metabolic diversity in R. sphaeroides enables the well-performed degradation of complex substrates for biofuel production.
The phototrophic purple nonsulfur bacterium Rhodopseudomonas palustris is known for its metabolic versatility and is of interest for various industrial and environmental applications. Despite decades of research on R....
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The phototrophic purple nonsulfur bacterium Rhodopseudomonas palustris is known for its metabolic versatility and is of interest for various industrial and environmental applications. Despite decades of research on R. palustris growth under diverse conditions, patterns of R. palustris growth and carbon utilization with mixtures of carbon substrates remain largely unknown. R. palustris readily utilizes most short-chain organic acids but cannot readily use lactate as a sole carbon source. Here we investigated the influence of mixed-substrate utilization on phototrophic lactate consumption by R. palustris. We found that lactate was simultaneously utilized with a variety of other organic acids and glycerol in time frames that were insufficient for R. palustris growth on lactate alone. Thus, lactate utilization by R. palustris was expedited by its coutilization with additional substrates. Separately, experiments using carbon pairs that did not contain lactate revealed acetate-mediated inhibition of glycerol utilization in R. palustris. This inhibition was specific to the acetate-glycerol pair, as R. palustris simultaneously utilized acetate or glycerol when either was paired with succinate or lactate. Overall, our results demonstrate that (i) R. palustris commonly employs simultaneous mixed-substrate utilization, (ii) mixed-substrate utilization expands the spectrum of readily utilized organic acids in this species, and (iii) R. palustris has the capacity to exert carbon catabolite control in a substrate-specific manner. IMPORTANCE Bacterial carbon source utilization is frequently assessed using cultures provided single carbon sources. However, the utilization of carbon mixtures by bacteria (i.e., mixed-substrate utilization) is of both fundamental and practical importance;it is central to bacterial physiology and ecology, and it influences the utility of bacteria as biotechnology. Here we investigated mixed-substrate utilization by the model organism Rhodopseudomonas pa
Co-consumption of formate by aerobic, glucose-limited chemostat cultures of Saccharomyces cerevisiae *** 113-7D led to an increased biomass yield relative to cultures grown on glucose as the sole carbon and energy sub...
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Co-consumption of formate by aerobic, glucose-limited chemostat cultures of Saccharomyces cerevisiae *** 113-7D led to an increased biomass yield relative to cultures grown on glucose as the sole carbon and energy substrate. In this respect, this strain differed from two previously investigated S. cerevisiae strains, in which formate oxidation did not lead to an increased biomass yield on glucose. Enzyme assays confirmed the presence of a formate-inducible, cytosolic and NAD(+)-dependent formate dehydrogenase. To investigate whether this enzyme activity was entirely encoded by the previously reported FDH1 gene, an fdh1Delta null mutant was constructed. This mutant strain still contained formate dehydrogenase activity and remained capable of co-consumption of formate. The formate dehydrogenase activity in the mutant was demonstrated to be encoded by a second structural gene for formate dehydrogenase (FDH2) in S. cerevisiae *** 113-7D. FDH2 was highly homologous to FDH1 and consisted of a fusion of two open reading frames (ORFs) (YPL275w and YPL276w) reported in the S. cerevisiae genome databases. Sequence analysis confirmed that, in the database genetic background, the presence of two single-nucleotide differences led to two truncated ORFs rather than the full-length FDH2 gene present in strain CENYK 113-7D. In the latter strain background an fdh1Deltafdh2Delta double mutant lacked formate dehydrogenase activity and was unable to co-consume formate. Absence of formate dehydrogenase activity did not affect growth on glucose as sole carbon source, but led to a reduced biomass yield on glucose-formate mixtures. These findings are consistent with a role of formate dehydrogenase in the detoxification of exogenous formate. Copyright (C) 2002 John Wiley Sons, Ltd.
Candida utilis CBS 621 and Saccharomyces cerevisiae CBS 8066 were grown in glucose-limited chemostat cultures with formate as an additional energy source. In both yeasts formate was oxidized via a cytoplasmic NAD+-lin...
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Candida utilis CBS 621 and Saccharomyces cerevisiae CBS 8066 were grown in glucose-limited chemostat cultures with formate as an additional energy source. In both yeasts formate was oxidized via a cytoplasmic NAD+-linked formate dehydrogenase. Other formate-oxidizing enzymes could not be detected. With Candida utilis the steady-state cell yield on glucose increased with increasing amounts of formate in the medium until growth became carbon-limited. The maximum growth yield on glucose in the presence of excess formate was dependent on the nitrogen source used for growth. With ammonium and nitrate the maximum yields were 0.69 and 0.56 g cells/g glucose, respectively. Calculations showed that this difference correlates with the NADPH requirement for biomass formation with these two nitrogen sources. This implies that the NADP produced from formate oxidation cannot replace the NADPH needed for biomass formation. It therefore is concluded that in Candida utilis transhydrogenase activity is absent. Also, Saccharomyces cerevisiae was capable of oxidizing formate in glucose-limited chemostat cultures. However, in contrast to Candida utilis utilization of formate by this yeast did not enhance the cell yield on glucose.
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