DddQ, a novel, cupin-containing, dimethylsulfoniopropionate lyase in marine roseobacters and in uncultured marine bacteria

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SummaryRuegeria(previouslySilicibacter)pomeroyiDSS-3, a marine roseobacter, can catabolize dimethylsulfoniopropionate (DMSP), a compatible solute that is made in large amounts by marine plankton and algae. This strain was known to demethylate DMSP via a demethylase, encoded by thedmdAgene, and it can also cleave DMSP, releasing the environmentally important volatile dimethyl sulfide (DMS) in the process. We found that this strain has two different genes,dddPanddddQ,which encode enzymes that cleave DMSP, generating DMS plus acrylate. DddP had earlier been found in other roseobacters and is a member of the M24 family of peptidases. The newly discovered DddQ polypeptide contains a predicted cupin metal-binding pocket, but has no other similarity to any other polypeptide with known function. DddP- and DddQ- mutants each produced DMS at significantly reduced levels compared with wild-typeR. pomeroyiDSS-3, and transcription of the correspondingdddgenes was enhanced when cells were pre-grown with DMSP. Ruegeria pomeroyiDSS-3 also has a gene product that is homologous to DddD, a previously identified enzyme that cleaves DMSP, but which forms DMS plus 3-OH-propionate as the initial catabolites. However, mutations in thisdddD-like gene did not affect DMS production, and it was not transcribed under our conditions. Another roseobacter strain,Roseovarius nubinhibensISM, also containsdddPand has two functional copies ofdddQ,encoded by adjacent genes. Judged by their frequencies in the Global Ocean Sampling metagenomic databases, DddP and DddQ are relatively abundant among marine bacteria compared with the previously identified DddL and DddD enzymes.

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