Submitted to: Biopesticides International
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 12, 2008
Publication Date: May 16, 2008
Citation: Martin, P.A.W., Blackburn, M.B. 2008. Characterization of the insectididal activity of Chromobacterium subtsugae. Biopesticide International. 4:102-109.
Interpretive Summary: Colorado potato beetle is a pest on potatoes and related crops: tomatoes and eggplant. Control costs and damage caused by this insect can exceed $100 million annually. This beetle has quickly developed resistance to various chemical insecticides; therefore alternatives are needed for continued control. We have discovered a species of violet bacteria, Chromobacterium subtsugae that produces toxins that kill Colorado potato beetles in laboratory tests. Live bacteria are not necessary to kill beetles, but the production of heat-stable toxins appears to be density dependent. Several independent lines of evidence suggested that the toxins are located in the bacterial cell membrane. Scientists can use this information to improve production of C. subtsugae toxins to kill Colorado potato beetles and use this information gathered in the laboratory to control beetles on farms
Chromobacterium subtsugae PRAA4-1 produces toxins orally active to Colorado potato beetle larvae and other pest insects. These toxins have proved difficult to characterize. In liquid medium, Principal component analysis suggested that the best correlation of toxicity to Colorado potato beetle was to optical density (r=0.78). Toxicity to Colorado potato beetle was not correlated to viable cell number, cell mass, protein concentration, pH, nor violacein pigment production. Isolated violacein pigment was not toxic to beetle larvae. In a reduced-peptone liquid medium, non-pigmented colonies appeared on the titer plates after 11 serial transfers. One stable non-pigmented mutant, PRAA4-1B was not toxic to Colorado potato beetle larvae. Using phenotypic microarrays, it was observed that PRAA4-1B grew 15% faster than the parent strain, and differed in its use of many nitrogen and phosphate sources, suggesting a regulatory mutation. The antibiotic resistance of the mutant was identical to the parent strain except, this mutant was also more resistant to polymixin B suggesting a membrane location for the toxin. The toxin could be extracted from non viable cells by detergents and was stable upon autoclaving suggesting that it is not a protein