Verrucomicrobia are candidates for polysaccharide-degrading bacterioplankton in an arctic fjord of Svalbard.

In Arctic marine bacterial communities, members of the phylum Verrucomicrobia are consistently detected, although not typically abundant, in 16S rRNA gene clone libraries and pyrotag surveys of the marine water column and in sediments. In an Arctic fjord (Smeerenburgfjord) of Svalbard, members of the Verrucomicrobia, together with Flavobacteria and smaller proportions of Alpha- and Gammaproteobacteria, constituted the most frequently detected bacterioplankton community members in 16S rRNA gene-based clone library analyses of the water column. Parallel measurements in the water column of the activities of six endo-acting polysaccharide hydrolases showed that chondroitin sulfate, laminarin, and xylan hydrolysis accounted for most of the activity. Several Verrucomicrobia water column phylotypes were affiliated with previously sequenced, glycoside hydrolase-rich genomes of individual Verrucomicrobia cells that bound fluorescently labeled laminarin and xylan and therefore constituted candidates for laminarin and xylan hydrolysis. In sediments, the bacterial community was dominated by different lineages of Verrucomicrobia, Bacteroidetes, and Proteobacteria but also included members of multiple phylum-level lineages not observed in the water column. This community hydrolyzed laminarin, xylan, chondroitin sulfate, and three additional polysaccharide substrates at high rates. Comparisons with data from the same fjord in the previous summer showed that the bacterial community in Smeerenburgfjord changed in composition, most conspicuously in the changing detection frequency of Verrucomicrobia in the water column. Nonetheless, in both years the community hydrolyzed the same polysaccharide substrates.

Prokaryote populations of extant microbialites along a depth gradient in Pavilion Lake, British Columbia, Canada.

Pavilion Lake in British Columbia, Canada, is home to modern-day microbialites that are actively growing at multiple depths within the lake. While microbialite morphology changes with depth and previous isotopic investigations suggested a biological role in the formation of these carbonate structures, little is known about their microbial communities. Microbialite samples acquired through the Pavilion Lake Research Project (PLRP) were first investigated for phototrophic populations using Cyanobacteria-specific primers and 16S rRNA gene cloning. These data were expounded on by high-throughput tagged sequencing analyses of the general bacteria population. These molecular analyses show that the microbial communities of Pavilion Lake microbialites are diverse compared to non-lithifying microbial mats also found in the lake. Phototrophs and heterotrophs were detected, including species from the recently described Chloroacidobacteria genus, a photoheterotroph that has not been previously observed in microbialite systems. Phototrophs were shown as the most influential contributors to community differences above and below 25 meters, and corresponding shifts in heterotrophic populations were observed at this interface as well. The isotopic composition of carbonate also mirrored this shift in community states. Comparisons to previous studies indicated this population shift may be a consequence of changes in lake chemistry at this depth. Microbial community composition did not correlate with changing microbialite morphology with depth, suggesting something other than community changes may be a key to observed variations in microbialite structure.