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

The biphenyl degradation pathway of Sphingomonas paucimobilis BPSI-3 was in vestigated using a degradation-deficient mutant generated by 1-methyl-3-nit ro-1-nitrosoguanidine (NTG) mutagenesis. The mutant, designated AN2, was co nfirmed as originating from BPSI-3 through the use of ERIC (Enterobacterial Repetitive Intergenic Consensus) PCR and by detection of the diagnostic pi gment, nostoxanthin, in cellular methanol extracts. Mutant AN2 produced a y ellow 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 consis tent with the characteristics of a quinone, 1-phenyl-2,3-benzoquinone, whic h could arise from the oxidation of 2,3-dihydroxybiphenyl. A quinone was sy nthesised from 2,3-dihydroxybiphenyl and compared to the red compound produ ced by mutant AN2. Gas chromatography-mass spectrophotometry (GC-MS) confir med that a similar quinone (4,5-dimethoxy-3-phenyl-1,2-benzoquinone) compar ed to the structure of the proposed biogenic compound, had been formed. Thi s compound was also found after GC-MS analysis of mutant AN2 culture extrac ts. Spectrophotometric analysis of the quinone synthesised and the red prod uct produced revealed almost identical spectral profiles. A likely inferenc e from this evidence is that the mutant AN2 is blocked, or its activity alt ered, in the first gene cluster, bphA to C, of the biphenyl degradation pat hway.