Analysis and interpretation of community-level physiological profiles in microbial ecology

A rapid, community-level approach for assessing patterns of sole carbon source utilization by mixed microbial samples has been used increasingly to study microbial community dynamics. The method involves direct inoculation of environmental samples into Biolog microtiter plates, and uses color formation from reduction of a tetrazolium dye to assess utilization of 95 separate sole carbon sources during a 2–7 day incubation period. This approach, called community-level physiological profiling, has been effective at distinguishing spatial and temporal changes in microbial communities. Effective analysis of the multivariate profiles of carbon source utilization requires separation of effects caused by differences in inoculum density (i.e. overall rate of color development) from effects caused by differences in the types or activities of organisms present (i.e. relative rates, or pattern, of carbon source utilization). Further experimental studies are required to better define what fraction of the original inoculum responds in the assay, and if the profiles provide structural and/or functional information.