Diversity and heterogeneity of epibiotic bacterial communities on the marine nematode Eubostrichus dianae

The diversity of a microbial community covering the surface of a marine nem atode was analyzed by performing a 16S ribosomal DNA (rDNA) restriction cut ting and sequencing analysis. In two clone libraries constructed by using i ndividual nematodes, 54 and 85 restriction patterns were identified, and on ly 13 of these patterns were common to both libraries. Sequence analysis in dicated that the common patterns belonged to four groups related to sequenc es of cytophagas, sulfate-reducing bacteria, members of the gamma subclass of the class Proteobacteria, and caulobacters. At least two groups appeared to be permanent members of the community as they were also detected in a 1 6S rDNA library constructed 3 years previously by using 100 pooled nematode specimens. A surprising outcome was that very dominant filamentous bacteri a were apparently not represented in the clone libraries, as quantitative p robing showed that none of the common operational taxonomic unit groups dis played the expected overwhelming dominance. Nevertheless, our analysis reve aled both an unexpectedly high level of bacterial diversity and heterogenei ty in samples representing presumably very similar microenvironments.