Absence of 4-Formylaminooxyvinylglycine production by Pseudomonas fluorescens WH6 results in resource reallocation from secondary metabolite production to rhizocompetence

Authors: Manning, Viola; Trippe, Kristin

Submitted to: Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/25/2021
Publication Date: 3/31/2021
Citation: Manning, V., Trippe, K.M. 2021. Absence of 4-Formylaminooxyvinylglycine production by Pseudomonas fluorescens WH6 results in resource reallocation from secondary metabolite production to rhizocompetence. Microbiology. 9(4). Article 717. https://doi.org/10.3390/microorganisms9040717.
DOI: https://doi.org/10.3390/microorganisms9040717

Interpretive Summary: Species in the bacterial genus Pseudomonas are well known for their ability to produce antibiotics and other bioactive compounds. Within the genus Pseudomonas, members of the P. fluorescens group produce an array of compounds that contribute to disease suppression and plant growth promotion. Some of these compounds have been adopted for use in human health and many are being explored as possible next-generation pesticides. Knowledge of how these compounds are produced and how they alter their ecosystems is fundamental if we are to harness their full potential. P. fluorescens (Pf) WH6 produces 4-formylaminooxyvinylglycine (FVG). This compound arrests the germination of grasses. While FVG has the potential to control the germination of annual grasses in perennial or non-grass crops, the bacterium does not produce sufficient FVG for commercial or biocontrol applications. To better understand how Pf WH6 regulates the production of FVG, we compared the transcriptomes of Pf WH6 strains that are unable to produce FVG with those that do. The gvg operon is known to encode the proteins that produce FVG. Three genes (gvgR, gvgA, and gvgC) within the gvg operon were evaluated for their ability to regulate expression of the genes involved in the production of FVG. Our analyses show that hundreds of genes, including the gvg operon, are differentially expressed in WH6 strains lacking the gvgR, A, or C genes compared to the wildtype bacterium. Our results suggest that FVG production is regulated by certain compounds, including acidic amino acids and their amines. We also found that, in the absence of FVG, Pf WH6 reallocates resources so that the bacterium can associate with roots. Altogether, the results of this study suggest that regulation of the FVG production is multifaceted and the absence of FVG production dramatically shifts the lifestyle of Pf WH6.

Technical Abstract: Pseudomonas fluorescens WH6 produces the non-proteinogenic amino acid 4-formylaminooxyvinylglycine (FVG), a secondary metabolite with antibacterial and pre-emergent herbicidal activities. The gvg operon necessary for FVG production encodes eight required genes: one regulatory (gvgR), two of unknown functional potential (gvgA and C), three with putative biosynthetic function (gvgF, H, and I), and two small ORFs (gvgB and G). To gain insight into the role of GvgA and C in FVG production, we performed comparative transcriptomics of knockout (KO) mutants of gvgR, A, and C versus wild type (WT) to test two hypotheses: 1) GvgA and GvgC play a regulatory role in FVG production and 2) non-gvg cluster genes are regulated by GvgA and GvgC. Our analyses show that hundreds of genes, including the gvg operon, are differentially expressed in all KO strains versus WT. Most genes are similarly regulated in all KO strains with GvgC having the greatest uniquely regulated genes. Additional transcriptome data suggest cluster regulation through feedback of a cluster product. Functional annotation of differentially expressed genes revealed that FVG biosynthesis is regulated by acidic amino acids and their amines and resources are reallocated in KO strains to increase phenotypes involved in rhizocompetence. 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.