Effect of sulfide on growth physiology and gene expression of Desulfovibrio vulgaris Hildenborough.

Hydrogen sulfide, the metabolic end product of sulfate-reducing bacteria (SRB), is toxic to most life forms. This includes the SRB themselves. Although many of these are probably among the most sulfide resistant life forms, the presence of sulfide nevertheless presents a stress, which SRB must overcome. Although the response of SRB, especially the genus Desulfovibrio, to numerous stressors has been studied, their response to sulfide stress is unknown. We determined the effect of sulfide stress by comparing cells of Desulfovibrio vulgaris Hildenborough grown under conditions in which sulfide accumulated (high sulfide, 10 mM) with cells grown under conditions in which sulfide was removed by continuous gassing (low sulfide, 1 mM). High sulfide decreased the instantaneous growth rate constant and the final cell density of the culture by 52 and 33%, respectively, indicating a decreased bioenergetic fitness. Changes in gene expression caused by exposure to high sulfide were determined using full-genome D. vulgaris microarrays. The transcription of ribosomal protein-encoding genes was decreased, in agreement with the lower growth rate of D. vulgaris under high sulfide conditions. Interestingly, expression of the gene for DsrD, located downstream of the genes for dissimilatory sulfite reductase was also strongly down-regulated. In contrast, the expression of many genes involved in iron accumulation, stress response and proteolysis were increased. This indicates that high sulfide represents a significant stress condition, in which the bioavailability of metals like iron may be lowered. Overall this leads to a reduced growth rate and less efficient biomass production.