Studies on microbial consortia degrading phenol in aqueous phase

Abstract

Microbial consortia have been identified as potent tools for waste treatment including discharges of toxic chemicals. Activated sludge is the most widely used microbial consortium in the waste water treatment. Knowledge of the factors that determine the growth, stability and performance of the consortium are essential for achieving optimum results on waste water purification. The present research was focused on gaining more insight on the structure and stability of a phenol degrading consortium which was developed and maintained in a fed-batch reactor by feeding 500 mg phenol/1/day. Analysis of the consortium has shown that it was consisted of 8 phenol degrading bacteria and 2 non-phenol bacteria which belonged to the genera of Bacillus, Streptomyces, Pseudomonas and Rhodococcus with varied phenol degradation and growth in phenol or its derivatives. The best phenol degrading isolates (AS5) could remove 400 mg phenol during 24 hours, while the slow phenol degrader (AS7) of the consortium could remove only 120 mg phenol from the above concentration. The performance of a consortium would, naturally be guided by the functional characteristics of the constituent members. The attempt to study the population of phenol degrading consortium indicated that the individual population were under continuous shift and was not in the same scale. Despite the varied growth characteristics of individual members in the consortium stable performance was exhibited by the consortium. Significantly higher degradation rate of phenol was observed with the consortium than the individual isolate at varying concentration of phenol from 400 mg/l to 700 mg/l. Compared to pure culture, the consortium was better equipped for degradation of phenol in pure or mixture and under stressed conditions. The phenol degrading consortium in this study was constituted of a highly heterogeneous population in terms of their morphology (size, shape, pigmentation and gram reaction), biochemistry (presence of ortho and meta pathway for cleavage of phenol), physiology (ability to utilise variety of phenols, cresols, benzenes, catechol and resorcinol) and growth rate. The presence of two non-phenol bacteria in the consortium added more heterogeneity to the system. The stability and degradation rate of the consortium were superior to those of mixed cultures made from less heterogeneic members. These observations made us to conclude that the stability of a microbial consortium is found to be conformed through the diverse characteristics of its constituent members. A completely functional and stable consortium could be established slowly in 3 months period by reconstituting all isolates of the consortium. Before it reached its final stage of stability a lot of changes was noticed in the system. However, the exact reason for the delay in attaining the stability was not clear from the reconstitution studies.