Genes involved in hydrogen and sulfur metabolism in phototrophic sulfur bacteria

The dsr genes and the hydSL operon are present as separate entities in phototrophic sulfur oxidizers of the genera Allochromatium, Marichromatium, Thiocapsa and Thiocystis and are organized similarly as in Allochromatium vinosum and Thiocapsa roseopersicina, respectively. The dsrA gene, encoding the alpha subunit of 'reverse' siroheme sulfite reductase, is also present in two species of green sulfur bacteria pointing to an important and universal role of this enzyme and probably other proteins encoded in the dsr locus in the oxidation of stored sulfur by phototrophic bacteria. The hupSL genes are uniformly present in the members of the Chromatiaceae family tested. The two genes between hydS and hydL encode a membrane-bound b-type cytochrome and a soluble iron-sulfur protein, respectively, resembling subunits of heterodisulfide reductase from methanogenic archaea. These genes are similar but not identical to dsrM and dsrK, indicating that the derived proteins have distinct functions, the former in hydrogen metabolism and the latter in oxidative sulfur metabolism.     

Cleavage of dimethylsulfoniopropionate and reduction of acrylate by Desulfovibrio acrylicus sp. nov.

From anoxic intertidal sediment, a dimethylsulfoniopropionate (DMSP)-cleaving anaerobe (strain W218) was isolated that reduced the acrylate formed to propionate. The bacterium was vibrio- to rod-shaped and motile by means of multiple polar flagella. It reduced sulfate, thiosulfate, and acrylate, and used lactate, fumarate, succinate, malate, pyruvate, ethanol, propanol, glycerol, glycine, serine, alanine, cysteine, hydrogen, and formate as electron donors. Sulfate and acrylate were reduced simultaneously; growth with sulfate was faster than with acrylate. Extracts of cells grown in the presence of DMSP contained high DMSP lyase activities (9.8 U/mg protein). The DNA mol% G+C was 45.1. On the basis of its characteristics and the 16S rRNA gene sequence, strain W218 was assigned to a new Desulfovibrio species for which the name Desulfovibrio acrylicus is proposed. A variety of other sulfate-reducing bacteria (eight of them originating from a marine or saline environment and five from other environments) did not reduce acrylate. Received: 22 March 1996 / Accepted: 8 May 1996     

Isolation and characterization of an environmental acid-fast organism producing diphenoloxidase activity in vivo

Water and soil samples were collected from natural habitats of the nine-banded armadillo and tested for the presence of acid-fast organisms by injection into the foot pads of experimental mice. Sixteen months post inoculation an acid-fast organism was isolated from the foot pad and spleen of one of the mice. The isolate exhibited diphenoloxidase activity as determined by its ability to convert D-3,4-dihydroxyphenylalanine to the corresponding quinone. The same organisms grown in vitro lacked detectable diphenoloxidase activity. However, diphenoloxidase activity was observed in acid-fast organisms harvested from spleen tissue of mice experimentally inoculated with a pure culture of the isolate. The environmental isolate was tentatively classed with the Mycobacterium avium-intracellulare complex.