Comparative actinomycete diversity in marine sédiments

The diversity of cultured actinomycete bacteria was compared between near- and off-shore marine sediments. Strains were tested for the effects of seawater on growth and analyzed for 16S rRNA gene sequence diversity. In total, 623 strains representing 6 families in the order Actinomycetales were cultured. These strains were binned into 16 to 63 operational taxonomic units (OTUs) over a range of 97 to 100% sequence identity. The majority of the OTUs were closely related (>98% sequence identity) to strains previously reported from non-marine sources, indicating that most are not restricted to the sea. However, new OTUs averaged 96.6% sequence identity with previously cultured strains and ca. one-third of the OTUs were marine-specific, suggesting that sediment communities include considerable actinomycete diversity that does not occur on land. Marine specificity did not increase at the off-shore sites, indicating high levels of terrestrial influence out to 125 km from shore. The requirement of seawater for growth was observed among