Microbial natural products remain an important resource for drug discovery yet the microorganisms inhabiting the world's oceans have largely been overlooked in this regard. The recent discovery of novel secondary metabolites from taxonomically unique populations of marine actinomycetes suggests that these bacteria add an important new dimension to microbial natural product research. Continued efforts to characterize marine actinomycete diversity and how adaptations to the marine environment affect secondary metabolite production will create a better understanding of the potential utility of these bacteria as a source of useful products for biotechnology.

Actinomycetes were cultivated using a variety of media and selective isolation techniques from 275 marine samples collected around the island of Guam. In total, 6425 actinomycete colonies were observed and 983 (15%) of these, representing the range of morphological diversity observed from each sample, were obtained in pure culture. The majority of the strains isolated (58%) required seawater for growth indicating a high degree of marine adaptation. The dominant actinomycete recovered (568 strains) belonged to the seawater-requiring marine taxon 'Salinospora', a new genus within the family Micromonosporaceae. A formal description of this taxon has been accepted for publication (Maldonado et al., 2005) and includes a revision of the generic epithet to Salinispora gen. nov. Members of two major new clades related to Streptomyces spp., tentatively called MAR2 and MAR3, were cultivated and appear to represent new genera within the Streptomycetaceae. In total, five new marine phylotypes, including two within the Thermomonosporaceae that appear to represent new taxa, were obtained in culture. These results support the existence of taxonomically diverse populations of phylogenetically distinct actinomycetes residing in the marine environment. These bacteria can be readily cultured using low nutrient media and represent an unexplored resource for pharmaceutical drug discovery.