Biodegradation of a BTX mixture by Pseudomonas stains: monitoring of two co-cultured strains by polymerase chain reaction of catabolic genes

Pseudomonas putida CM37, Pseudomonas aureofaciens CM32 and Pseudomonas putida CM23 degraded toluene through different pathways. CM37 carried xylA,M gene for xylene monooxygenase (TOL pathway), CM32 carried todC1 gene for toluene dioxygenase (TOD pathway) and CM23 carried both genes and was characterised by the contemporary presence of TOL and TOD pathways. In this study we compared the behaviour of these strains grown on a limiting concentration of a benzene, toluene and m-xylene (BTX) mixture as the carbon and energy source. Moreover, the competition between the two Pseudomonas strains CM37 and CM32 was monitored during BTX degradation when co-cultured in batch experiments by both colony culturing and molecular techniques. A polymerase chain reaction (PCR) quantitative method of enumeration was set up on xylA,M and todC1 catabolic genes. The two enumeration meth- ods showed satisfactory agreement and revealed CM32 to be the most competitive strain when co-cultured with CM37 on the BTX mixture. Application of PCR detection of aromatic catabolic genes enabled to enumerate selectively bacterial strains preferring benzene, toluene or m-xylene.