EVIDENCE FOR INDIGENOUS STREPTOMYCES POPULATIONS IN A MARINE-ENVIRONMENT DETERMINED WITH A 16S RIBOSOMAL-RNA PROBE

A 16S rRNA genus-specific probe was used to determine whether Streptom yces populations are an indigenous component of marine sediment bacter ial communities. Previous debates have suggested that marine Streptomy ces isolates are derived not from resident populations but from spores of terrestrial species which have been physically transported to mari ne ecosystems but remain dormant until isolation. Rigorously controlle d hybridizations of rRNA extracted from coastal marsh sediments with t he genus-specific probe indicated that Streptomyces rRNA accounted for 2 to 5% of the sediment community rRNA and that spores are not the so urce of the hybridization signal. Streptomyces populations must theref ore be at least the 26th most abundant genus-level source of bacterial rRNA. The relative amounts of rRNAs from Streptomyces spp. and member s of the Bacteria (69 to 79%) and Archaea (4 to 7%) domains were highl y consistent in these marine sediments throughout an annual cycle, ind icating that the species composition of sediment bacterial communities may be more stable than recent: studies suggest for marine planktonic bacterial communities. Laboratory studies designed to investigate the possible functional roles of Streptomyces populations in coastal sedi ments demonstrated that population levels of this genus changed relati vely rapidly (within a time frame of 6 weeks) in response to manipulat ion of substrate availability. Amendments of intact sediment cores wit h two compounds (vanillic acid and succinic acid) consistently resulte d in Streptomyces populations contributing an increased percentage of rRNA (6 to 15%) to the total bacterial rRNA pool.