Absence of 4-Formylaminooxyvinylglycine Production by <i>Pseudomonas fluorescens</i> WH6 Results in Resource Reallocation from Secondary Metabolite Production to Rhizocompetence

• Main Authors: Viola A. Manning, Kristin M. Trippe
• Format: Article
• Language: English
• Published: MDPI AG 2021-03-01
• Series: Microorganisms
• Subjects: vinylglycine; regulation of secondary metabolites; <i>Pseudomonas fluorescens</i>; natural herbicide
• Online Access: https://www.mdpi.com/2076-2607/9/4/717

<i>Pseudomonas fluorescens</i> WH6 produces the non-proteinogenic amino acid 4-formylaminooxyvinylglycine (FVG), a secondary metabolite with antibacterial and pre-emergent herbicidal activities. The <i>gvg</i> operon necessary for FVG production encodes eight required genes: one regulatory (<i>gvgR</i>), two of unknown functional potential (<i>gvgA</i> and <i>C</i>), three with putative biosynthetic function (<i>gvgF</i>, <i>H</i>, and <i>I</i>), and two small ORFs (<i>gvgB</i> and <i>G</i>). To gain insight into the role of GvgA and C in FVG production, we compared the transcriptome of knockout (KO) mutants of <i>gvgR</i>, <i>A</i>, and <i>C</i> to wild type (WT) to test two hypotheses: (1) GvgA and GvgC play a regulatory role in FVG production and (2) non-<i>gvg</i> cluster genes are regulated by GvgA and GvgC. Our analyses show that, collectively, 687 genes, including the <i>gvg</i> operon, are differentially expressed in all KO strains versus WT, representing >10% of the genome. Fifty-one percent of these genes were similarly regulated in all KO strains with GvgC having the greatest number of uniquely regulated genes. Additional transcriptome data suggest cluster regulation through feedback of a cluster product. We also discovered that FVG biosynthesis is regulated by L-glu, L-asp, L-gln, and L-asn and that resources are reallocated in KO strains to increase phenotypes involved in rhizocompetence including motility, biofilm formation, and denitrification. Altogether, differential transcriptome analyses of mutants suggest that regulation of the cluster is multifaceted and the absence of FVG production or its downregulation can dramatically shift the lifestyle of WH6.