Widespread and persistent populations of a major new marine actinomycete taxon in ocean sediments

Abstract

A major taxon of obligate marine bacteria within the order Actinomycetales has been discovered from ocean sediments. Populations of these bacteria (designated MAR 1) are persistent and widespread, spanning at least three distinct ocean systems. In this study, 212 actinomycete isolates possessing MAR 1 morphologies were examined and all but two displayed an obligate requirement of seawater for growth. Forty-five of these isolates, representing all observed seawater-requiring morphotypes, were partially sequenced and found to share characteristic small-subunit rRNA signature nucleotides between positions 207 and 468 (Escherichia coli numbering). Phylogenetic characterization of seven representative isolates based on almost complete sequences of genes encoding 16S rRNA (16S ribosomal DNA) yielded a monophyletic clade within the family Micromonosporaceae and suggests novelty at the genus level. This is the first evidence for the existence of widespread populations of obligate marine actinomycetes. Organic extracts from cultured members of this new group exhibit remarkable biological activity, suggesting that they represent a prolific resource for biotechnological applications.

FIG. 1.

Phylogenetic relationships determined from almost complete 16S rDNA sequences of select MAR 1 isolates, CNB512 and CNB394 (Micromonospora spp.) and representatives of all 10 presently accepted genera within the Micromonosporaceae (9, 18, 22). Bootstrap values (in percent) calculated from 1,000 resamplings using neighbor-joining (value on left) and parsimony methods (value on right) are shown at their respective nodes when the values calculated using at least one method were 70% or greater. Propionibacterium propionicum, Streptosporangium corrugatum, and Streptomyces lividans were used as outgroups.