An attempt was made at using the symbiotic relationship between the sulfate-reducing (SR) bacteria and sulfide-oxidizing (SO) bacteria for the degradation of organic matter present in wastewater. Major emphasis was on the development of the desired microbial system without any external seed and comparative evaluation of the two types of multistage reversing flow bioreactor systems. Two bench-scale models - one designed to achieve self-granulation of sludge (SGS), and one designed to promote growth of the symbiotic bacteria on additional nonreactive surface - were set up and operated over a period of 4 months. Several visual and microscopic observations confirmed the presence of a significant number of SR and SO bacteria in all the biological vessels. Results indicated that it is possible to develop SGS and a microbial population of SR and SO bacteria which could attach to the nonreactive surface without any external seeding.