Insecticidal features displayed by the beneficial rhizobacterium Pseudomonas chlororaphis PCL1606

Abstract The biocontrol rhizobacterium Pseudomonas chlororaphis is one of the bacterial species of the P. fluorescens group where insecticide fit genes have been found. Fit toxin, supported with other antimicrobial compounds, gives the bacterial capacity to repel and fight against predators, such as nematodes and insect larvae, thus protecting the plant host and itself. Pseudomonas chlororaphis PCL1606 is an antagonistic rhizobacterium isolated from avocado roots with efficient biocontrol against fungal soil-borne disease. The main antimicrobial compound produced by P. chlororaphis PCL606 is 2-hexyl,5-propyl resorcinol (HPR), which plays a crucial role in effective biocontrol against fungal pathogens. Further analysis of the P. chlororaphis PCL1606 genome showed the presence of hydrogen cyanide (HCN), pyrrolnitrin (PRN) and homologous fit genes. To test the insecticidal activity and to determine the bases for such activity, single and double mutants on the biosynthetic genes of these four compounds were tested in a Galleria mellonella larval model using inoculation by injection. The results revealed that fit toxin and HPR are the main compounds responsible for the insecticide phenotype in P. chlororaphis PCL1606, and HCN and PRN could be considered supporting compounds.