Bacterial communities in a northeast Ohio stream: Effects of substrate size, environmental features and temporal changes

Examination of bacterial communities in lotic biofilms can aid understanding of the processes driving their presence. Organic matter utilization, detritus availability, geomorphology and hydrodynamics, along with temporal and spatial variation are all influences on bacterial communities. The focus of this research was to examine factors affecting bacterial communities in a lotic ecosystem. Field studies and in situ experiments were completed in the West Branch of the Mahoning River in Northeast Ohio from October 2000 through August 2004. Total numbers of bacteria were determined via epifluorescent microscopy using DAPI stain. Additionally, fluorescently labeled taxon-specific probes were hybridized with cellular rRNA to determine the abundance of specific taxa. The Domain Bacteria, Proteobacteria (alpha and gamma groups), and Cytophaga-Flavobacterium were enumerated via epifluorescent microcopy. Multiple habitats (water, leaves and sediments) were compared during 2000--2001, and greatest stability in abundance was in the sediments. A second seasonal study during 2003--2004 focused on bacteria colonizing various size sediments and showed differences in abundance among the different size categories. Species-specific probes included Burkholderia cepacia (beta-Proteobacteria) and Acinetobacter calcoaceticus (gamma-Proteobacteria). Supporting physical and chemical data were also collected during field studies. Experiments examined the impact of sediment grain size on bacteria using glass beads of different diameters (0.1 mm, 1.0 mm, 5.0 mm) and unglazed ceramic tiles incubated in situ in packets made of plankton netting. Effects of incubation habitat (riffle versus pool) and organic matter addition (dried maple leaves) were tested. A microcosm experiment tested the premise that bacteria incubated in situ on one bead size would respond differently when inoculated onto a different bead size.; The field surveys revealed temporal variation in communities in the various habitats, with more stability in the sediments. Natural and artificial substrata showed significant differences generally between the 0.1 mm and 5.0 mm beads or tiles. In most instances the community composition was fairly consistent. Of all taxa examined, B. cepacia was the least responsive to variations in environmental conditions. Surface area, did not entirely account for differences in abundance on the substrates; it is evident that other physical processes also affect utilization and abundance.