UC San Diego

In the past 150 years, marine microbial ecology has followed and exciting journey. Beginning with the isolation of a few marine bacteria, it went on to establish the omnipresence of these microorganisms in the marine environment as well as their crucial roles in global nutrient and carbon cycles. Advances in molecular techniques have allowed the study of the microbial realm including the exploration of the whole ocean's microbial genes. It is underneath the ocean and covering over 70% of our planet that lays an incredible reservoir of 1x109 bacteria per gram of marine sediment. This environment represents a new frontier for microbial diversity, including that of marine actinomycetes. These Gram- positive, high G+C content, filamentous bacteria have been extensively studied due to their widely known ability to produce bioactive secondary metabolites. The diversity of cultured actinomycete bacteria was compared between near- shore and offshore marine sediments. Results revealed that even though the requirement of seawater for growth is not a common trait among marine-derived actinomycetes, there are high levels of marine adaptation among some lineages. At the same time, marine sediment communities include considerable actinomycete diversity that does not occur on land (33-35% marine specific Operational Taxonomic Units at 98% sequence identity) including distinct marine OTU clades whose richness increases in offshore sediments. High terrestrial influence was observed out to 100 km from shore, at the same time, statistical analyses suggest higher actinomycete diversity at offshore locations. Cultivation independent studies on the Families Streptomycetaceae and Micromonosporaceae revealed a broader snapshot of their diversity in the marine sediment samples. This study also exposed the importance of a polyphasic approach towards the assessment of actinomycete diversity in marine sediments. Distinct OTUs were observed when compared to cultivated Sterptomycetaceae and Micromonosporaceae diversity, yet the phylogenetic distribution of both communities (cultivated and environmental) did not significantly differ from each other. This method supported observations reported during the cultivation-dependent study suggesting a more extensive diversity of members of these actinomycete families in offshore marine sediments. Cultivation efforts rendered novel groups of marine-derived actinomycetes. The phylogenetic novelty of these groups and the diversity of bioactive natural products they produce, including three new chemical types, are discussed