Sphingomonas paucimobilis BPSI-3 mutant AN2 produces a red catabolite during biphenyl degradation

The biphenyl degradation pathway of Sphingomonas paucimobilis BPSI-3 was investigated using a degradation-deficient mutant generated by 1-methyl-3-nitro-1-nitrosoguanidine (NTG) mutagenesis. The mutant, designated AN2, was confirmed as originating from BPSI-3 through the use of ERIC (Enterobacterial Repetitive Intergenic Consensus) PCR and by detection of the diagnostic pigment, nostoxanthin, in cellular methanol extracts. Mutant AN2 produced a yellow followed by red extracellular substance when grown in the presence of biphenyl. In the presence of 2,3-dihydroxybiphenyl, yellow followed by red then yellow compounds were formed over time. This colour change was consistent with the characteristics of a quinone, 1-phenyl-2,3-benzoquinone, which could arise from the oxidation of 2,3-dihydroxybiphenyl. A quinone was synthesised from 2,3-dihydroxybiphenyl and compared to the red compound produced by mutant AN2. Gas chromatography-mass spectrophotometry (GC-MS) confirmed that a similar quinone (4,5-dimethoxy-3-phenyl-1,2-benzoquinone) compared to the structure of the proposed biogenic compound, had been formed. This compound was also found after GC-MS analysis of mutant AN2 culture extracts. Spectrophotometric analysis of the quinone synthesised and the red product produced revealed almost identical spectral profiles. A likely inference from this evidence is that the mutant AN2 is blocked, or its activity altered, in the first gene cluster, bphA to C, of the biphenyl degradation pathway. Received 19 April 1999/ Accepted in revised form 25 July 1999