Novel rhodococci and other mycolate actinomycetes from the deep sea

A large number of mycolate actinomycetes have been recovered from deep-sea sediments in the NW Pacific Ocean using selective isolation methods. The is olates were putatively assigned to the genus Rhodococcus on the basis of co lony characteristics and mycolic acid profiles. The diversity among these i solates and their relationship to type strains of Rhodococcus and other myc olate taxa were assessed by Curie point pyrolysis mass spectrometry (PyMS). Three major (A, C, D) and two minor (B, E) groups were defined by PyMS. Cl uster A was a large group of isolates recovered from sediment in the Izu Bo nin Trench (2679 m); Cluster C comprised isolates from both the Izu Bonin T rench (6390 and 6499 m) and from the Japan Trench (4418, 6048 and 6455 m). These Cluster C isolates showed close similarity to Dietzia maris and this was subsequently confirmed using molecular methods. Cluster D contained iso lates recovered from a sediment taken from a depth of 1168m in Sagami Bay a nd were identified as members of the terrestrial species Rhodococcus luteus . Clusters B and E had close affinities with members of the genera Gordonia and Mycobacterium. The presence of Thermoactinomyces in certain of the dee p-sea sediments studied was indicative of the movement of terrestrial mater ial into the ocean depths. 16S ribosomal RNA gene sequence analyses produced excellent definition of m ost genera of the mycolata, and indicated that the among the deep sea isola tes (1) were novel species of Corynebacterium, Gordonia and Mycobacterium, and (2) a Sea of Japan isolate the phylogenetic depth of which suggests the possibility of a new genus. Polyphasic taxonomic analysis revealed conside rable diversity among the deep sea rhodococci and evidence for recently div erged species or DNA groups.