Multiple DMSP lyases in the γ-proteobacterium Oceanimonas doudoroffii

The marine gamma-proteobacterium Oceanimonas doudoroffii was shown to have at least three different enzymes, each of which can cleave dimethylsulfoniopropionate (DMSP), an abundant compatible solute made by different classes of marine phytoplankton. These various DMSP lyases have similarities, but also some differences to those that had been identified in other bacteria. This was demonstrated by cloning each of the corresponding genes and transferring them into other species of bacteria in which backgrounds they conferred the ability to catabolise DMSP, releasing dimethyl sulfide (DMS) as one of the products (Ddd(+) phenotype; DMSP-dependent DMS). One of these genes resembled dddD, which was in a cluster with other ddd genes variously involved in subsequent steps of DMSP catabolism, in DMSP import and in DMSP-dependent transcriptional regulation. The other two gene products both had sequence similarity to the previously identified DddP lyase. However, these two Oceanimonas DddP polypeptides were not particularly similar to each other and were in two different sub-branches compared to those that had been studied in strains of the Roseobacter clade of bacteria. One of these O. doudoroffii enzymes, DddP1, most closely resembled gene products in a disparate group of microbes that included two bacteria, Vibrio orientalis and Puniceispirillum marinum and, more strikingly, some Ascomycete fungi that can catabolise DMSP. Previously, the only bacteria known to have multiple ways to catabolise DMSP were in the Roseobacter clade, which were also the only bacteria that had been shown to have functional DddP DMSP lyases. Thus Oceanimonas doudoroffii is unusual on more than one count and likely acquired its dddD, dddP1 and dddP2 genes by independent horizontal gene transfer events.