Schmidt, J. L.. University of Washington,
Jumars, P. L.. University of Washington,

Little is known about the processes, particularly protozoan grazing, that control abundance or cell-specific activity of bacteria in marine sediments. Experimental investigations on the impact of grazing are difficult because the methods themselves significantly alter microbial dynamics. Significant grazing may produce a biased distribution of bacteria in the protective crevices of grain-grain contacts. However, efforts to visualize the locations of bacteria by traditional microscopy either disrupt habitat structure or do not provide enough spatial coverage to gain the statistical power needed to test predictions. We developed a method to quantify the spatial distribution of bacteria in native, surficial marine sediments. Samples (approximately 1 cm3) were collected from intertidal sands (False Bay, WA). Stains and fixative were added to the overlying water and allowed to diffuse into the pore fluid. After a series of graded ethanol and acetone replacements of pore fluid, epoxy was perfused into the sample. Hardened samples were prepared for microscopy using petrographic thin-sectioning techniques. Confocal and epifluorescence microscopy were then used to locate single bacteria, and assess their metabolic state, in 3D. Activity clearly is more spatially variable than is abundance, but data in hand as of this writing do not yet confirm or reject the existence of spatial refuges from predation.
Day: Friday, Feb. 5
Time: 12:00 - 12:15pm
Location: Sweeney Center
Code: CS63FR1200S