Lawrence Berkeley National Laboratory

The sulfate-reducing bacteria (SRB) are a heterologous group of anaerobic bacteria linked by their ability to respire the costly substrate sulfate as an electron acceptor and as a source of sulfur for cellular biosynthesis. All of the SRB organisms, of which D. vulgaris is a member, apparently share the same pathway for sulfate reduction, including an activation step involving the conversion of sulfate to adenosine-phosphosulfate (APS), which consumes two ATP equivalents. The enzyme complex involved in the activation step is APS-reductase, comprised of the two proteins, ApsB and ApsA. In D. vulgaris the apsBA genes are predicted to be the first two genes in a six gene operon. The three genes that immediately follow apsBA are qmoABC (Quinone-interacting membrane-bound oxidoreductase) that are conserved in all the genomes of SRB sequenced to date. We have deleted these three genes (and a hypothetical protein predicted to be present at the end of the operon, DVU0851) in D. vulgaris and monitored the strain s ability to grow in the presence of sulfate or sulfite. Here we describe the method of deleting these four genes and the growth characteristics of the construct. As predicted by its genomic location, the Qmo complex is essential for APS reduction and sulfate respiration but not sulfite respiration.