Nitrogen-dependent regulation of medium-chain length polyhydroxyalkanoate biosynthesis genes in pseudomonads.

Comparative transcriptional analysis of polyhdroxyalkanoate (PHA) biosynthesis genes with wild type strains and mutants, which lack the intact alternative sigma factor gene rpoN, was performed using semi-quantitative RT-PCR. In Pseudomonas putida and Pseudomonas aeruginosa, phaI and phaF were co-transcribed. PhaF was a negative regulator of transcription of PHA synthase gene phaC1 but did not serve as auto-repressor. However, the alternative sigma factor RpoN is suggested as negative regulator of phaF transcription. In P. putida, phaI-phaF transcription is strongly dependent on nitrogen availability and PHA accumulation, whereas phaF transcription is not. These data suggested a differential regulation of phaF and phaIF. The phaC1 gene transcription occurred almost independently by of RpoN or nitrogen availability in both pseudomonads.