Highly similar prokaryotic communities of sunken wood at shallow and deep-sea sites across the oceans.

With an increased appreciation of the frequency of their occurrence, large organic falls such as sunken wood and whale carcasses have become important to consider in the ecology of the oceans. Organic-rich deep-sea falls may play a major role in the dispersal and evolution of chemoautotrophic communities at the ocean floor, and chemosynthetic symbiotic, free-living, and attached microorganisms may drive the primary production at these communities. However, little is known about the microbiota thriving in and around organic falls. Our aim was to investigate and compare free-living and attached communities of bacteria and archaea from artificially immersed and naturally sunken wood logs with varying characteristics at several sites in the deep sea and in shallow water to address basic questions on the microbial ecology of sunken wood. Multivariate indirect ordination analyses of capillary electrophoresis single-stranded conformation polymorphisms (CE-SSCP) fingerprinting profiles demonstrated high similarity of bacterial and archaeal assemblages present in timbers and logs situated at geographically distant sites and at different depths of immersion. This similarity implies that wood falls harbor a specialized microbiota as observed in other ecosystems when the same environmental conditions reoccur. Scanning and transmission electron microscopy observations combined with multivariate direct gradient analysis of Bacteria CE-SSCP profiles demonstrate that type of wood (hard vs. softwood), and time of immersion are important in structuring sunken wood bacterial communities. Archaeal populations were present only in samples with substantial signs of decay, which were also more similar in their bacterial assemblages, providing indirect evidence of temporal succession in the microbial communities that develop in and around wood falls.