Seasonal patterns of substrate utilization by bacterioplankton: case studies in four temperate lakes of different latitudes

Utilization of 95 carbon sources by bacteria in 2 Canadian Shield lakes and 2 Texan reservoirs was determined using Biolog-GN microtiter plates. Tripl icate plates were inoculated and incubated for 5 d, during which color deve lopment was monitored twice daily by optical density (OD595) Optical densit ies in plate wells containing carbon substrates were corrected for blank ab sorbance at each measurement time. Then, data on optical densities of all s ubstrate wells were selected from a single measurement time, to construct a community-level physiological profile. This measurement time was chosen so that plates would be compared at similar levels of color development. This data selection also generally maximized correlations of substrate utilizat ion patterns determined from replicate plates. Multivariate analyses (ordin ations) of the community-level physiological profiles identified several am ino acids, carboxylic acids, and carbohydrates associated with seasonal pat terns of substrate utilization. Multivariate analyses further revealed patt erns in substrate utilization common to all 4 lakes: strong relative respon ses to amino and carboxylic acids in cool seasons and strong relative respo nses to carbohydrates in warm seasons. These patterns may be driven by seas onal events among phytoplankton that influence carbohydrate supply, and app ear to be dampened in an oligotrophic lake, which does not support high alg al abundance.