Highly Similar Prokaryotic Communities of Sunken Wood at Shallow and Deep-Sea Sites Across the Oceans

Abstract

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.

Temporal and spatial constraints on community assembly during microbial colonization of wood in seawater

“…The results showed how local environmental features could influence bacterial community assembly, but contrasting results have been reported. In one case, similar communities were present in woods situated at geographically distant sites and at different depths of immersion (Palacios et al, 2009). While in other cases, the location of the wood inside a submarine canyon Bessette et al, 2014), in the vicinity of carbonate crust (Bienhold et al, 2013), or its colonization by wood-boring Xylophaga bivalves strongly structured the microbial communities.…”

“…It demonstrated the presence of sequences associated to possible fermenters and sulfide-oxidizing bacteria, as well as the co-occurrence of free-living sulfate-reducing bacteria. Archaea have also been detected on wood falls, especially on samples with substantial signs of decay (Palacios et al, 2009). They are potentially involved in the production of methane (Fagervold et al, 2012), but the observation of the association of a giant Thaumarchaeota with sulfur-oxidizing bacteria (Muller et al, 2010) suggests the presence of diverse archaeal metabolisms on wood falls.…”

“…The first insight into the ecology of wood falls bacteria communities was published recently through experimental deployments of woods in the sea (Palacios et al, 2009;Bienhold et al, 2013;Fagervold et al, 2013). The results showed how local environmental features could influence bacterial community assembly, but contrasting results have been reported.…”

“…While in other cases, the location of the wood inside a submarine canyon Bessette et al, 2014), in the vicinity of carbonate crust (Bienhold et al, 2013), or its colonization by wood-boring Xylophaga bivalves strongly structured the microbial communities. The type of wood may also be important in structuring sunken wood bacterial communities (Palacios et al, 2009;Fagervold et al, 2013). Data on community ecology remain, however, rare, as they require experimental approaches that are particularly challenging in the deep sea.…”

“…Evidences of possible differences in community composition between the different parts of the wood are, for instance, lacking, and there are no direct evidences of temporal succession in the microbial communities. Previous studies relied on samples collected solely after several month of immersion (Palacios et al, 2009;Bienhold et al, 2013;Fagervold et al, 2013), which made it difficult to study the temporal dynamics of microbial wood colonization and community assembly.…”