SELF-MOBILIZATION AND ORGANIZATION OF THE GENES ENCODING THE TOLUENE METABOLIC PATHWAY OF PSEUDOMONAS-MENDOCINA KR1

The toluene metabolic pathway of Pseudomonas mendocina KR1 is chromoso mally encoded, but the pathway could be transferred by conjugation fro m strain KR1 to the chromosome of P. aeruginosa or P. putida. Such tra nsconjugants utilized toluene, p-cresol, and p-hydroxybenzaldehyde. Ho wever, transconjugants were unable to further transfer toluene genes t o other recipients unless Pseudomonas sex factor R68.45 was present in trans. Although the genes encoding the upper pathway for toluene meta bolism in P. mendocina KR1 are sufficiently linked to permit their coo rdinate mobilization, they were found to be encoded in three independe ntly regulated units: one encoding toluene-4-monooxygenase, a second e ncoding p-cresol methylhydroxylase and p-hydroxybenzaldehyde dehydroge nase, and a third encoding p-hydroxybenzoate hydroxylase. The last two regulatory units were cloned from the chromosome of a P. aeruginosa t ransconjugant onto a plasmid designated pRO1999. Analysis of pRO1999 s howed that genes encoding p-cresol methylhydroxylase and p-hydroxybenz aldehyde dehydrogenase are organized as an operon; the gene encoding p -hydroxybenzaldehyde dehydrogenase is transcribed first, and this is f ollowed by transcription of the gene encoding p-cresol methylhydroxyla se. This operon is regulated by a positively acting regulator. The P. mendocina KR1 gene encoding p-hydroxybenzoate hydroxylase was linked t o, but independently regulated from, the genes encoding toluene-4-mono oxygenase, p-cresol methylhydroxylase, and p-hydroxybenzaldehyde dehyd rogenase.