Abstract
Microbes of the Cytophaga-Flavobacterium (CF) group, within the phylum Bacteroidetes, have been considered contributors to the early decomposition of particulate organic matter (POM) in sediments because of their abundance in the ecosystem and their great ability to degrade macromolecules on artificial media. However, there is no report on the ability of members of this group to decompose POM in sediment. We investigated the POM-decomposition capabilities of members of the CF group, Flavobacterium limicola strains ST-82T, ST-10 and ST-92 isolated from freshwater sediment as proteolytic psychrophiles, in sterilized sediment slurries. All strains of F. limicola grew and survived at over 108 cfu per ml for more than 30 days in the sediment slurries at 5°C. Protease activity levels in the slurries inoculated with the strains were 3-5 times higher than the control level for over 30 days of incubation at 5°C. Concentrations of total dissolved nitrogen (TDN) released by the hydrolysis of particulate organic nitrogen (PON), significantly increased only in the slurries inoculated with F. limicola strains. Approximately 70-80% of the TDN released was converted to NH4+-N in these inoculated slurries. The results clearly demonstrate that F. limicola strains ST-82T, ST-10 and ST-92 are able to secrete an extracellular protease and hydrolyze PON to TDN and thereby mineralize TDN to NH4+-N in freshwater sediment. This is the first report on the decomposition and mineralization of PON by members of the CF group in benthic environments.
