Distributions of total and active bacteria in biofilms lining tubes of the onuphid polychaete Diopatra cuprea

Abstract

Infaunal burrows and tubes support elevated levels of microbial biomass and activities relative to the surrounding bulk sediments. The impacts of these structures on sediment biogeochemistry have been intensively studied, but very little is known about the microbiota or their spatial organization within these microenvironments. Distributions of bacterial cells and microcolonies and of potentially active bacterial cells in tubes of the onuphid polychaete Diopatra cuprea were determined using confocal scanning laser microscopy. Distributions were examined among different tubes, at different locations within a tube, and at different depths in the biofilms lining these tubes. The average quantity of cells across all tubes examined was 5.61 x 108 cm-3 and there was no trend in the distribution of cells along the length of the tube or with increasing depth in the biofilm. Cell size across all tubes collected in February 1997 averaged 0.085 μm3 but varied seasonally. Mean cell size increased with increasing depth below the sediment surface of the tube site sampled, and decreased with increasing depth in the biofilm. Microcolonies were abundant and not confined to specific depths within the biofilm or locations within the tube. Potentially active cells were observed at all depths within the biofilm and at least 46% (mean = 68%) of cells at any given site were potentially active. We hypothesize that the observed trends in cell distribution are responsive to tube irrigation by the host polychaete.