Microbial metabolism of 2-chlorophenol, phenol and rho-cresol by Rhodococcus erythropolis M1 in co-culture with Pseudomonas fluorescens P1

Chlorophenolic waste most often contains phenol and rho-cresol along with chlorophenols. A Rhodococcus erythropolis strain M1 was isolated with the ability to degrade 2-chlorophenol, phenol and p-cresol (100 mgl(-1), each) in 18, 24 and 20 h, respectively, with negligible lag. However, Rhodococcus sp. characterized by low growth rate, pose a threat to be outgrown by bacteria occurring in natural habitats. In the present study, interaction of R. erythropolis M1 with another isolated bacteria generally encountered in activated sludge for water treatment like Pseudomonas fluorescens P1 was studied. 2-chlorophenol, phenol and p-cresol were selected as the substrates for the study. Viable cell counts showed competitive interaction between the species on 2-chlorophenol and phenol. Specific growth rate of pure culture of R. erythropolis M1 was higher than P. fluorescens P1 on 2-chlorophenol. However, in mixed culture, P. fluorescens P1 showed higher growth rate. Degradation of phenol showed higher growth rate of R. erythropolis M1 both in pure and in mixed culture form. Degradation of p-cresol had shown similar counts for both populations indicating neutral type of interaction. This observation was substantiated by detecting the growth rate, where both cultures had similar growth rate in pure and in the mixed culture form. Rate of 2-chlorophenol degradation was higher when R. erythropolis M1 was used as the pure culture as compared to the degradation rates observed with the P. fluorescens P1 or with the mixed culture. However, in case of phenol and p-cresol, degradation by the mixed culture had resulted in higher degradation rates as compared to the degradation of the substrates by both the axenic cultures.