Characterization of Toxin Complex Gene Clusters and Insect Toxicity of Bacteria Representing Four Subgroups of Pseudomonas fluorescens

PLoS One. 2016 Aug 31;11(8):e0161120. doi: 10.1371/journal.pone.0161120. eCollection 2016.

Abstract

Ten strains representing four lineages of the Pseudomonas fluorescens group (P. chlororaphis, P. corrugata, P. koreensis, and P. fluorescens subgroups) were evaluated for toxicity to the tobacco hornworm Manduca sexta and the common fruit fly Drosophila melanogaster. The three strains within the P. chlororaphis subgroup exhibited both oral and injectable toxicity to the lepidopteran M. sexta. All three strains have the gene cluster encoding the FitD insect toxin and a ΔfitD mutant of P. protegens strain Pf-5 exhibited diminished oral toxicity compared to the wildtype strain. Only one of the three strains, P. protegens Pf-5, exhibited substantial levels of oral toxicity against the dipteran D. melanogaster. Three strains in the P. fluorescens subgroup, which lack fitD, consistently showed significant levels of injectable toxicity against M. sexta. In contrast, the oral toxicity of these strains against D. melanogaster was variable between experiments, with only one strain, Pseudomonas sp. BG33R, causing significant levels of mortality in repeated experiments. Toxin complex (Tc) gene clusters, which encode insecticidal properties in Photorhabdus luminescens, were identified in the genomes of seven of the ten strains evaluated in this study. Within those seven genomes, six types of Tc gene clusters were identified, distinguished by gene content, organization and genomic location, but no correlation was observed between the presence of Tc genes and insect toxicity of the evaluated strains. Our results demonstrate that members of the P. fluorescens group have the capacity to kill insects by both FitD-dependent and independent mechanisms.

MeSH terms

  • Animals
  • Bacterial Proteins / genetics*
  • Bacterial Toxins / genetics*
  • Drosophila melanogaster
  • Manduca
  • Multigene Family*
  • Pseudomonas fluorescens / genetics*

Substances

  • Bacterial Proteins
  • Bacterial Toxins

Grants and funding

LIR was supported by a Provost’s Distinguished Graduate Fellowship from Oregon State University. This work was supported by Agriculture and Food Research Initiative Competitive Grant 2008-35600-18770 and 2011-67019-30192 from the United States Department of Agriculture National Institute of Food and Agriculture.