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 env ironmental samples were distinguished by the ability of the native het erotrophic microbial communities to oxidize 95 different sole carbon s ources 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 (acut e), 1 d, 2 d, and 1 d. The acute dose-response of Snake River bacterio plankton communities measured by AMR was compared to the dose-response of Photobacterium phosphoreun (used in the Microtox test) and a propr ietary mixed consortia (used in the Polytox test). In laboratory bioas say studies, CLPP AMR exhibited acute dose-response behavior over a gr eater range in copper concentrations and with less variability (per do se) than Microtox and Polytox. The acute sensitivity of CLPP AMR to co pper was roughly equal to Microtox and much greater than Polytox. Afte r a longer exposure (1 d) to copper, Snake River communities became mo re sensitive to copper but no additional effect was observed when the exposure was increased to 2 and 4 d. Snake River communities pre-expos ed 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, indic ating the ability of the assay to detect adaptation. Several metal-con taminated streams in Idaho were used to held validate the CLPP approac h for detecting impacts of metals in the environment. The response pro files of the bacterioplankton from two downstream sites receiving meta l laden mine drainage were compared to those from reference sites upst ream and further downstream of the location receiving the mine drainag e. The AMR of the communities at the stream reference sites were great er 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 unst ressed communities (reference stream sites). At the third site, treatm ent of mine drainage by an artificial wetland was assessed above and b elow the wetland; water exiting the treatment wetland had a higher AMR than water that was untreated. The CLPP approach has sufficient sensi tivity to detect acute contaminant impact on physiological processes o f the indigenous microbial community while providing data for evaluati on of chronic stress-induced adaptations in microbial community struct ure.