Deletion of the Desulfovibrio vulgaris Carbon Monoxide Sensor Invokes Global Changes in Transcription

Abstract

The carbon monoxide-sensing transcriptional factor CooA has been studied only in hydrogenogenic organisms that can grow using CO as the sole source of energy. Homologs for the canonical CO oxidation system, including CooA, CO dehydrogenase (CODH), and a CO-dependent Coo hydrogenase, are present in the sulfate-reducing bacterium Desulfovibrio vulgaris, although it grows only poorly on CO. We show that D. vulgaris Hildenborough has an active CO dehydrogenase capable of consuming exogenous CO and that the expression of the CO dehydrogenase, but not that of a gene annotated as encoding a Coo hydrogenase, is dependent on both CO and CooA. Carbon monoxide did not act as a general metabolic inhibitor, since growth of a strain deleted for cooA was inhibited by CO on lactate-sulfate but not pyruvate-sulfate. While the deletion strain did not accumulate CO in excess, as would have been expected if CooA were important in the cycling of CO as a metabolic intermediate, global transcriptional analyses suggested that CooA and CODH are used during normal metabolism. Desulfovibrio organisms are sulfate-reducing bacteria that use organic acids, alcohols, or molecular hydrogen as electron donors to reduce sulfate (22). When these bacteria grow on organic acids or alcohols, energy generation is hypothesized to be derived in part through hydrogen cycling (20). Hydrogen cycling posits that reducing equivalents formed during oxidation of the electron donor in the cytoplasm are shuttled to form hydrogen, which is then oxidized in the periplasm to generate electrons for sulfate reduction and to generate a proton motive force. This mechanism for energy recovery offers an explanation for the hydrogen burst observed during the early growth phase in batch culture (15,19,20,28). Desulfovibrio vulgaris Hildenborough appears well equipped to carry out this hydrogen cycling, possessing an array of six predicted hydrogenases-four localized periplasmically (Hyd, Hyn1, Hyn2, and Hys) and two membrane-bound enzymes facing the cytoplasm (Coo and Ech) (12). There is also some evidence suggesting that, in addition to hydrogen, carbon monoxide functions as either a growth substrate or an intermediate in energy metabolism (16,29).With the exception of some Desulfotomaculum species that can grow in Ͼ50% CO, CO is toxic at concentrations of Ͻ20% to most sulfate-reducing bacteria (21). CO toxicity is likely to be a result of inhibition of hydrogenases or other metalloenzymes (21). CO has been demonstrated to be both produced and consumed by Desulfovibrio spp. CO production has been documented during growth of both D. vulgaris Hildenborough (29) and D. vulgaris Madison (16) on lactate-sulfate or pyruvate-sulfate, with greater accumulation in a D. vulgaris Hildenborough hyd mutant lacking the periplasmic Fe hydrogenase (29). Consumption was demonstrated in D. vulgaris strain Madison. This organism grew on a headspace of 4% CO as the sole energy source and tolerated a headspace of 4.5% CO while growing on organic acids, consistent with the presence of an acti...

Regulation of Nitrite Stress Response in Desulfovibrio vulgaris Hildenborough, a Model Sulfate-Reducing Bacterium

“…vulgaris growth conditions. D. vulgaris was grown in defined medium containing 8 mM MgCl 2 , 20 mM NH 4 Cl, 2.2 mM K 2 PO 4 , 0.6 mM CaCl 2 , 30 mM Tris, 1 ml/liter of Thauer's vitamins (37), 12.5 ml/liter of trace element solution (38), and 640 l/liter of resazurin (0.1%) and supplemented with 50 mM Na 2 SO 4 and 60 mM sodium lactate (LS4D medium). The pH of the medium was adjusted to 7.2 with 1 N HCl.…”

Gasotransmitters, poisons, and antimicrobials: it's a gas, gas, gas!

“…However, homologues of this canonical CO oxidation system, including CooA, CO dehydrogenase, and a CO-dependent Coo hydrogenase, are also present in the sulfate-reducing bacterium Desulfovibrio vulgaris , although it grows only poorly on CO. Recent global transcriptional analyses suggests that CooA and CO dehydrogenase are used during normal metabolism of this bacterium [66]. Another haem-containing CO sensor, RcoM from Burkholderia xenovorans , which is also able to bind NO, regulates the expression of genes in response to the redox state of the cell [67,68].…”

The Carbon Monoxide Dehydrogenase from Desulfovibrio vulgaris

“…Desulfovibrio vulgaris (Dv) contains an annotated CODH operon containing two genes that encode for the CODH enzyme (cooS) and a maturase (cooC) [34] but these enzymes have not been characterized so far. The CO-dependent expression of this operon is regulated by a transcriptional regulator (CooA), the encoding gene of which is located upstream [34].…”

“…The CO-dependent expression of this operon is regulated by a transcriptional regulator (CooA), the encoding gene of which is located upstream [34]. Although Dv does not grow on CO as sole energy source, Dv is able to consume exogenous CO [34] and to produce CO under certain conditions [35].…”