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

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.

The Gac/Rsm Signaling Pathway of a Biocontrol Bacterium, Pseudomonas chlororaphis O6

“…In pathogens, the Gac sensor kinase system controls virulence gene expression (Heeb and Haas, 2001). It is also found that the Gac/Rsm system of PcO6 is required for the expression of the insecticidal activity to the tobacco hornworm (Rangel et al, 2016), and to the root knot nematode (Lee et al, 2011(Lee et al, , 2017. In addition, the Gac system is shown to be important in expression of gene expression in the inhibition of fungal growth by PcO6 Oh et al, 2013a;Park et al, 2011).…”

“…Hosts other than plants also are affected by colonization with PcO6, because this bacterium possessed insecticidal capacity. This bacterium showed insecticidal activity on the tobacco hornworm (Rangel et al, 2016) and on nematodes (Lee et al, 2011).…”

Conserved architecture of Tc toxins from human and insect pathogenic bacteria

“…TcAs are not only present in insects and human pathogenic bacteria, but they have been also identified in plant pathogenic bacteria such as Pseudomonas syringae and Pseudomonas fluorescens 31 . Although we have not studied TcA from these bacteria, based on our study, we propose that all TcAs, including those of plant pathogenic bacteria share the same architecture and mechanism of action.…”

Isolation and characterization of Pseudomonas cedrina infecting Plutella xylostella (Lepidoptera: Plutellidae)

“…Furthermore, based on the phylogenetic analysis, P. cedrina was clustered into fluorescens subgroup and certain strains of fluorescens subgroup exhibited insecticidal activity. In addition, two types of insect toxin genes: fluorescens insecticidal toxin (FitD) and Toxin complex (Tc) proteins have been identified (Rangel et al, ; Ruffner et al, ). However, in this study, supernatant of P. cedrina lost larvicidal activity, while supernatant of B. thuringiensis exhibited high larvicidal activity.…”

“…The neighbor‐joining phylogenetic tree was constructed by MEGA5.1 with the closest sequences from NCBI and related 16S rRNA of Pseudomonas spp. from Rangel et al ().…”