Physiological profiling of indigenous aquatic microbial communities to determine toxic effects of metals

Conventional bioassays for environmental assessment frequently rely on nonindigenous single species. We employed an assay in which whole environmental samples were distinguished by the ability of the native heterotrophic microbial communities to oxidize 95 different sole carbon sources generating a community‐level physiological profile (CLPP). The average metabolic response (AMR) to the 95 variables defining the CLPP was used in laboratory bioassay studies with copper to construct dose–response curves over several different periods of exposure: 1 h (acute), 1 d, 2 d, and 4 d. The acute dose–response of Snake River bacterioplankton communities measured by AMR was compared to the dose–response of Photobacterium phosphoreum (used in the Microtox test) and a proprietary mixed consortia (used in the Polytox test). In laboratory bioassay studies, CLPP AMR exhibited acute dose–response behavior over a greater range in copper concentrations and with less variability (per dose) than Microtox and Polytox. The acute sensitivity of CLPP AMR to copper was roughly equal to Microtox and much greater than Polytox. After a longer exposure (1 d) to copper, Snake River communities became more sensitive to copper but no additional effect was observed when the exposure was increased to 2 and 4 d. Snake River communities pre‐exposed to copper (1 mg/L) for 4 d prior to acute dose–response experiments showed no difference in AMR with respect to doses up to 10 mg/L, indicating the ability of the assay to detect adaptation. Several metal‐contaminated streams in Idaho were used to field validate the CLPP approach for detecting impacts of metals in the environment. The response profiles of the bacterioplankton from two downstream sites receiving metal laden mine drainage were compared to those from reference sites upstream and further downstream of the location receiving the mine drainage. The AMR of the communities at the stream reference sites were greater than sites just below the mines. We ascribed this finding to acute physiological insult near the mines and subsequent recovery downstream. Multivariate analysis revealed differences in the pattern of carbon source utilization between chronically stressed (mine waters) and unstressed communities (reference stream sites). At the third site, treatment of mine drainage by an artificial wetland was assessed above and below the wetland; water exiting the treatment wetland had a higher AMR than water that was untreated. The CLPP approac