TAXONOMY AND BIOTRANSFORMATION ACTIVITIES OF SOME DEEP-SEA ACTINOMYCETES

Deep-sea soft sediments from trench systems and depths in the northwes tern Pacific Ocean ranging from less than 300 to 10 897m in depth have been analyzed for three target genera of actinomycetes: Micromonospor a, Rhodococcus, and Streptomyces. Only culturable strains, recovered a t atmospheric pressure on selective isolation media, have been examine d to date. Maximum recoveries of culturable bacteria were greater that 10(7)/ml wet g sediment, but actinomycetes comprised a small proporti on of this population (usually less than 1%). The target actinomycetes were isolated at all depths except from the Mariana Trench sediments. Actinomycete colonies were defined initially on the basis of colony m orphologies, and preliminary identification then was made by chemotaxo nomic tests. Pyrolysis mass spectrometry (PyMS) of deep-sea mycolic ac id-containing actinomycetes gave excellent correspondence with numeric al (phenetic) taxonomic analyses and subsequently was adopted as a rap id procedure for assessing taxonomic diversity. PyMS analysis enabled several clusters of deep-sea rhodococci to be distinguished that are q uite distinct from all type strains. 16S rRNA gene sequence analysis h as revealed that several of these marine rhodococci have sequences tha t are very similar to certain terrestrial species of Rhodococcus and t o Dietzia. There is evidence for the intrusion of terrestrial runoff i nto these deep trench systems, and the inconsistency of the phenotypic and molecular taxonomies may reflect recent speciation events in acti nomycetes under the high-pressure conditions of the deep sea. The resu lts of DNA-DNA pairing experiments point to the novelty of Rhodococcus strains recovered from hadal depths in the Izu Bonin Trench. Biotrans formation studies of deep-sea bacteria have focused on nitrile compoun ds. Nitrile-metabolizing bacteria, closely related to rhodococci, have been isolated that grow well at low temperature, high salt concentrat ions, and high pressures, suggesting that they are of marine origin or have adapted to the deep-sea environment.