SYNERGISTIC GROWTH OF 2 MEMBERS FROM A MIXED MICROBIAL CONSORTIUM GROWING AN BIPHENYL

A stable nine-membered aerobic bacterial consortium (BSEN-2) growing o n biphenyl as the sole carbon and energy source was isolated from a po lychlorinated biphenyl (PCB) contaminated soil. Characterisation of th e members, strains BPSI-1 to 9, revealed three principal genera, Pseud omonas, Sphingomonas and Alcaligenes. Phenotypic analysis based on sta ndard microbiological tests and Biolog identification, showed close re lationships between community members with the exception of Sphingomon as paucimobilis strain BPSI-3, Some clusters revealed relationships un related to genus groupings. Strain BPSI-3 produced a bright yellow wat er soluble compound from biphenyl having absorption maxima at 412 and 337 nm at neutral pH. This is similar, but not identical, to those res ults reported for muconic semialdehydes, cleavage products of biphenyl and other aromatic compounds. Only four of the nine isolates, BPSI-2, 3, 4 and 7, were capable of growth on biphenyl as sole carbon and ene rgy source. Two isolates, Alcaligenes faecalis type II strain BPSI-2 a nd S. paucimobilis strain BPSI-3, were isolated together and were diff icult to separate into pure cultures. Growth studies in liquid culture showed that a co-culture of these two achieved a specific growth rate (mu) approximately twice as high as strain BPSI-2 and four times that of BPSI-3. Both strains grew equally well on benzoate with no signifi cant difference in their specific growth rates. When compared to the o riginal mixed culture, BSEN-2, the co-culture achieved 39% greater bio mass and a specific growth rate twice as high. In the co-culture, the yellow colour seen with pure cultures of BPSI-3 was not observed. BPSI -2 was found to be able to utilise the yellow metabolites more effecti vely than BPSI-3. A model for the interaction of these two strains, ba sed on the utilisation of biphenyl catabolites and degradation at the genetic level, has been proposed.