Temporal Changes in the Bacterial Assemblage of a Northeast Ohio Stream: A Comparison of Community and Population-Level Responses

Abstract

Few studies have documented temporal changes in bacterial communities in multiple habitats in streams. In this year long study in the West Branch of the Mahoning River in Northeast Ohio, USA, bacteria in water, leaves, and sediments were examined. Bacteria were enumerated using 4,6-diamidino-2-phenylindole (DAPI) and fluorescent in situ hybridization (FISH) using taxon-specific probes for the Domain Bacteria and Burkholderia cepacia. Physical and chemical variables were also monitored. Total bacterial abundance in water (based on DAPI staining) peaked during October 2000 and July 2001; while on leaves, total abundance peaked in January then declined through April with a second June peak. The peak in sediments was during October 2000 and numbers did not differ significantly between a pool and a riffle. Domain Bacteria numbers also exhibited significant temporal changes but the seasonal patterns differed from those based on DAPI staining. Abundance of B. cepacia varied temporally on leaves but not in water and sediments. Contrary to other studies, no significant correlations were seen between bacteriological and physical/chemical variables measured. However, spring run off seems to have been a factor in temporarily reduced numbers on leaves and sediments and increasing bacterioplankton numbers, likely due to allochthonous inputs. Based on prior studies, we expected the pattern of temporal change in bacterial numbers to vary among habitats. However, there were no differences between pool and riffle sediments and no significant correlations between bacteriological and abiotic variables. This may reflect the ability of bacteria to persist under varying temperature/nutrient conditions and flow regimes. The ability of B. cepacia to maintain fairly constant populations, in contrast to the overall assemblage, likely reflects the extreme versatility of this organism.