Microbial population shift of anaerobic sludge consortia in response to temperature change was investigated by using 16S rRNA molecular approach such as FISH (fluorescent in situ hybridization), PCR-RFLPsequencing and T-RFLP (Terminal Restriction Fragment Length Polymorphism). A bench scale UASB reactor maintained at 35°C for a long time period was subjected to abrupt temperature increase to 55°C. The mesophilic granular sludge exhibited the optimum methanogenic activity, opposed to our anticipation, at above 40°C, while the thermophilic granular sludge possesses the optimum methanogenic activity at different temperatures for each different substrate: 55°C for propionate-, 60°C for acetate-, and 65°C for hydrogen-fed methanogenic activity.
FISH analysis using our newly developed oligoneucleotide probes, which are able to distinguish separately mesophilic and thermophilic acetate-utilizing methanogen, successfully provided an evidence that some extent of Methanosaeta thermophilia, thermophilic acetate-utilizing methanogen, is present a priori in the mesophilic sludge consortium that have never experienced a thermophilic condition in the past.
The T-RFLP patterns of archaeral clones' 16S rDNA reflected distinctly the time-series population shift from mesophilic acetate-utilizing methanogen (Methanosaeta concilii) to thermopilic acetate-utilizing methanogen (Methanosaeta thermophilia). The molecular approach methodology employed in this study proved to be powerful and useful tools to monitor the population dynamics of anaerobic sludge consortia for better understanding of anaerobic wastewater processes.
