Diversity of Micromonospora strains from the deep Mediterranean Sea and their potential to produce bioactive compounds

During studies on bacteria from the Eastern Mediterranean deep-sea, incubation under in situ conditions (salinity, temperature and pressure) and heat treatment were used to selectively enrich representatives of Micromonospora. From sediments of the Ierapetra Basin (4400 m depth) and the Herodotos Plain (2800 m depth), 21 isolates were identified as members of the genus Micromonospora. According to phylogenetic analysis of 16S rRNA gene sequences, the Micromonospora isolates could be assigned to 14 different phylotypes with an exclusion limit of >= 99.5% sequence similarity. They formed 7 phylogenetic clusters. Two of these clusters, which contain isolates obtained after enrichment under pressure incubation and phylogenetically are distinct from representative reference organism, could represent bacteria specifically adapted to the conditions in situ and to life in these deep-sea sediments. The majority of the Micromonospora isolates (90%) contained at least one gene cluster for biosynthesis of secondary metabolites for non-ribosomal polypeptides and polyketides (polyketide synthases type I and type II). The determination of biological activities of culture extracts revealed that almost half of the strains produced substances inhibitory to the growth of Gram-positive bacteria. Chemical analyses of culture extracts demonstrated the presence of different metabolite profiles also in closely related strains. Therefore, deep-sea Micromonospora isolates are considered to have a large potential for the production of new antibiotic compounds.