Cadmium induced adaptive responses of certain biogeochemical cycling bacteria in an aquatic system

The population growth of some biogeochemical cycling bacteria (heterotrophic bacteria (HB), ammonifying bacteria (AB), ammonia oxidizing bacteria (AOB), denitrifying bacteria (DNB) and cellulose decomposing bacteria (CDB)), as well as ammonification, and denitrification rates were determined in simulated pond systems treated with full doses (FDs) and split doses (SDs) of cadmium. Reductions in bacterial density and nitrogen activity rates were more severe for the FD and SD followed by a slight recovery in both. Among the test groups, reductions were maximal in the AOB and DNB and lowest for the CDB populations, suggesting that the latter had greater potential for cadmium resistance. Bicarbonate alkalinity of water was found to exert a profound influence in counteracting cadmium stress in the system, as strong negative correlations between this parameter and bacterial mass were evident in the SD treatment. Though the aquatic microbial populations were greatly altered by cadmium stress, the normal operating range of the system was restored at a later time with the CDB population showing higher degree of adaptive responses.