Improved growth rate in hydrogenase mutant via perturbed sulfur metabolism.

BACKGROUND

Metabolic engineering is a commonly used approach to develop organisms for an industrial function, but engineering aimed at improving one phenotype can negatively impact other phenotypes. This lack of robustness can prove problematic. Cellulolytic bacterium is able to rapidly ferment cellulose to ethanol and other products. Recently, genes involved in H production, including the hydrogenase maturase and NiFe hydrogenase , were deleted from the chromosome of . While ethanol yield increased, the growth rate of Δ decreased substantially compared to wild type.

RESULTS

Addition of 5 mM acetate to the growth medium improved the growth rate in , whereas wild type remained unaffected. Transcriptomic analysis of the wild type showed essentially no response to the addition of acetate. However, in , 204 and 56 genes were significantly differentially regulated relative to wild type in the absence and presence of acetate, respectively. Genes, Clo1313_0108-0125, which are predicted to encode a sulfate transport system and sulfate assimilatory pathway, were drastically upregulated in in the presence of added acetate. A similar pattern was seen with proteomics. Further physiological characterization demonstrated an increase in sulfide synthesis and elimination of cysteine consumption in . had a higher growth rate than in the absence of added acetate, and a similar but less pronounced transcriptional and physiological effect was seen in this strain upon addition of acetate.

CONCLUSIONS

Sulfur metabolism is perturbed in strains, likely to increase flux through sulfate reduction to act either as an electron sink to balance redox reactions or to offset an unknown deficiency in sulfur assimilation.