Massetolide A Biosynthesis inPseudomonas fluorescens

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Abstract
Massetolide A is a cyclic lipopeptide (CLP) antibiotic produced by variousPseudomonasstrains from diverse environments. Cloning, sequencing, site-directed mutagenesis, and complementation showed that massetolide A biosynthesis inP. fluorescensSS101 is governed by three nonribosomal peptide synthetase (NRPS) genes, designatedmassA,massB, andmassC, spanning approximately 30 kb. Prediction of the nature and configuration of the amino acids by in silico analysis of adenylation and condensation domains of the NRPSs was consistent with the chemically determined structure of the peptide moiety of massetolide A. Structural analysis of massetolide A derivatives produced by SS101 indicated that most of the variations in the peptide moiety occur at amino acid positions 4 and 9. Regions flanking themassgenes contained several genes found in otherPseudomonasCLP biosynthesis clusters, which encode LuxR-type transcriptional regulators, ABC transporters, and an RND-like outer membrane protein. In contrast to mostPseudomonasCLP gene clusters known to date, themassgenes are not physically linked but are organized in two separate clusters, withmassAdisconnected frommassBandmassC. Quantitative real-time PCR analysis indicated that transcription ofmassCis strongly reduced whenmassBis mutated, suggesting that these two genes function in an operon, whereas transcription ofmassAis independent ofmassBCand vice versa. Massetolide A is produced in the early exponential growth phase, and biosynthesis appears not to be regulated byN-acylhomoserine lactone-based quorum sensing. Massetolide A production is essential in swarming motility ofP. fluorescensSS101 and plays an important role in biofilm formation.

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