Dimethylsulfide (DMS) production from dimethylsulfoniopropionate by freshwater river sediments: phylogeny of Gram-positive DMS-producing isolates

Abstract

Freshwater river sediments from both the Coastal Plain and Piedmont regions of South Carolina showed high rates of dimethylsulfide (DMS) production from added dimethylsulfoniopropionate (DMSP). These rates were considered to be high as they were ca. 1% of rates in salt marsh sediments. Most probable number enumeration of DMS producers in river water and sediments were also about 1% of those measured in estuarine water and salt marsh sediment. Tellurite and DMSP enrichments resulted in the isolation of tellurite-resistant Gram-positive nocardia-like DMS producers from freshwater, but not marine sediments. Gram-negative DMS producers, all capable of growth on DMSP, were isolated from both freshwater and salt marsh sediments. Sequencing the 16S rRNA genes of the most common freshwater isolates showed they were closely related to Rhodococcus equi and Rhodococcus rhodochrous, members of the family Nocardiaceae. This group, which made up 73% of the total number of freshwater sediment isolates, belonged to the phylogenetic class of high-GC, Gram-positive bacteria, a newly recognized group of DMS producers. The origin of DMSP-dependent DMS producers in a freshwater, nearly DMSP-free, environment is discussed.