Fluorescent in situ hybridization (FISH) for the detection of bacterial community in activated sludge from textile...

Conventional methods used to study the bacterial community structure in activated sludge are not sufficient enough to determine the compositions of the bacterial populations responsible for biodegradation. Activated sludge samples from 3 textile factories were analyzed by fluorescent in situ hybridization (FISH) using rRNA probes and by phase-contrast microscopy. In Factory-I, the predominant groups were the beta-subclass of Proteobacteria and the cytophaga-flavobacterium (CF) cluster (33.3% and 31.0%) followed by gamma-subclass (17.1%), high G+C DNA (HGC) gram-positive (15.4%) and alpha-subclass (3.2%). Factory-II showed a similar pattern (32.7%, 31.8%, 17.5%, 16.4%, 1.6%) but with lower concentrations, while Factory-III showed predominant alpha- and beta-subclasses (25.2%, 25.0%) and CF cluster (24.8%) followed by the gamma-subclass (13.6%) and the HGC (11.4%) at much lower concentrations. The floc characteristic for factory-I and -II was normal, however factory-III had diffuse and atypical flocs. In conclusion, the FISH technique provided comprehensive information on the bacterial consortia of activated sludge samples. The compositions of the bacterial community and their concentrations together with the floc characteristics might be some of the reasons that affect the operational efficiencies among the 3 textile factories.