A New Function of the Desulfovibrio vulgaris Hildenborough [Fe] Hydrogenase in the Protection against Oxidative Stress

Abstract

Sulfate-reducing bacteria, like Desulfovibrio vulgarisHildenborough, have developed a set of reactions allowing them to survive in oxic environments and even to reduce molecular oxygen to water. D. vulgaris contains a cytoplasmic superoxide reductase (SOR) and a periplasmic superoxide dismutase (SOD) involved in the elimination of superoxide anions. To assign the function of SOD, the periplasmic [Fe] hydrogenase activity was followed in both wild-type and sod deletant strains. This activity was lower in the strain lacking the SOD than in the wild-type when the cells were exposed to oxygen for a short time. The periplasmic SOD is thus involved in the protection of sensitive iron-sulfur-containing enzyme against superoxide-induced damages. Surprisingly, production of the periplasmic Microbial sulfate reduction has been reported to be an ancient process as old as 3.47 gigayears. Sulfate reduction thus represents an early specific metabolic pathway, allowing time calibration of a deep node on the tree of life (1). Sulfate-reducing bacteria (SRB) 1 are universally distributed in marine and microbial mats where sulfate reduction is the dominant anaerobic biomineralization pathway. They constitute a group of anaerobic prokaryotes, which are unified by sharing the capacity to carry out dissimilatory sulfate reduction to sulfide as a major component of their bioenergetic processes. Although sulfate reduction is generally considered to be an anaerobic process, the abundance and metabolic activity of SRB in oxic zones is frequently evaluated as higher than those in neighboring anoxic zones in numerous biotopes (2, 3). In situ detection of sulfate reducing activity and SRB populations in these biotopes showed that SRB species did not have the same capability of resisting oxygen. Analysis of the photooxic zone of cyanobacterial mats revealed a well-defined SRB distribution. Although Desulfobacter and Desulfobacterium were restricted to the deepest levels in the mats, Desulfococcus were predominant in the photooxic zone with Desulfovibrio also present. This distribution suggests that both groups contain oxygen-tolerant members (4). It is thus clear that SRB exhibit a differentiated set of reactions to oxygen: first, many SRB form aggregates (5), resulting in a higher tolerance to oxygen exposure; second, at least Desulfovibrio species migrate in response to the oxygen concentration in their environment (5); and third, many species respire with oxygen (6). However, although it has been demonstrated that aerobic respiration is coupled with proton translocation and ATP conservation, aerobic growth in pure culture has never been proved (7). The high respiration rate merely seems to have a protective function. In an oxygen gradient, bacteria form bands at the outer edge of the oxic zone, suggesting both negative and positive aerotaxis responses (8). The capability of SRB to move toward oxygen and reduce it might play an ecological role in the zone of transition from an oxic to an anoxic environment, protecting themselves and other...

Transcriptional response of Desulfovibrio vulgaris Hildenborough to oxidative stress mimicking environmental conditions

“…A large proportion of the highly up-regulated genes are grouped into cellular roles involved in protein fate, cell envelope, transport/binding and regulatory functions, whereas the functional group showing more pronounced down-regulation of genes was that of energy metabolism. Cell viability upon plating showed that counts are reduced to 30% (0.9x10 7 CFU/ml versus 3x10 7 CFU/ml) in agreement with a prior study using a similar treatment that reported a reduction to 23% in the number of CFU/ml (Fournier et al 2004). …”

“…This agrees with earlier biochemical studies that showed an increase of the cytochrome c content (Fournier et al 2004) since this complex includes the sixteen-heme cytochrome HmcA. The increase in the cytochrome content cannot be attributed to the type I cytochrome c 3 (DVU3171), the main cytochrome present in the periplasm (Louro 2007), because its gene was down-regulated.…”

“…Three different oxygen-reducing systems have been characterized in Desulfovibrio spp., a group of widely distributed SRB that have been intensively studied as model organisms for these bacteria: 1) a cytoplasmic electron transport chain terminating with the flavo-diiron protein rubredoxin-oxygen oxidoreductase (Roo) (Chen et al 1993); 2) a membrane-bound system involving a terminal cytochrome bd oxidase (Cyd) (Lemos et al 2001); and 3) a periplasmic H 2 -dependent system involving hydrogenases and c-type cytochromes (Baumgarten et al 2001;Fournier et al 2004). The genome sequences of D. vulgaris Hildenborough (Heidelberg et al 2004) and D. desulfuricans G20 (www.jgi.doe.gov) confirmed the presence of these pathways in both organisms, and also of a heme-copper-type terminal cytochrome c oxidase (Cox).…”

Extra-cellular chromate-reducing activity of the yeast cultures

“…Bacterial reduction of chromate is well-established and runs through the different enzymatic pathways functioning under aerobic [4] and anaerobic [5] conditions. Anaerobic bacteria can reduce chromate using hydrogenase [6], cytochrome c-dependent electron transfer chains [7,8]. Little is known about mechanisms of chromate reduction for aerobic bacteria, except some enzymes which are shown to catalyze this reaction in vitro, for example, nitrate reductase [9], flavin reductase [10], ferrireductase [11], and some flavoproteins [12,13].…”

A Thermostable Aspartate Aminotransferase from Aeropyrum pernix K1

“…The amino acid sequences encoded by the APE2423 gene also demonstrated approximately 42% identity to hydrogenase from Carboxydothermus hydrogenoformuns (Figure 1). When hydrogenase activity was assayed spectrophotometrically using reduced methyl viologen dichloride as a substrate, 10 however, the recombinant protein of APE2423 had no hydrogenase activity. Based on these results, we selected the APE2423 gene as a candidate for an AAT.…”