|Shapiro Ilan, David|
Submitted to: Journal of Industrial Microbiology and Biotechnology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/25/2006
Publication Date: 1/1/2007
Citation: Wang, Y., Bilgrami, A.L., Shapiro Ilan, D.I., Gaugler, R. 2007. Stability of entomopathogenic bacteria, Xenorhabdus nematophila and Photorhabdus luminescens, during in vitro culture. Journal of Industrial Microbiology and Biotechnology. 34:73-81. Interpretive Summary: Insect-killing nematodes are naturally occurring round worms that can be used as environmentally friendly bio-insecticides. The nematodes kill insects with the help of specialized bacteria that are carried in the nematode's gut. When these organisms are grown continuously in the laboratory or in industrial settings, beneficial characteristics can be lost due to potentially harmful genetic changes. In this study we characterized the loss of beneficial traits in two species of the bacteria. We determined that bacterial growth can increase as the cultures are grown repeatedly and the bacteria adapt to environmental conditions. However, we also observed detrimental effects, i.e., that virulence (killing power), cell size, and nutritional characteristics can decline when the bacteria are repeatedly cultured. This information is important for designing mass production processes for these beneficial organisms.
Technical Abstract: The entomopathogenic nematode-bacteria complexes Heterorhabditis bacteriophora/Photorhabdus luminescens and Steinernema carpocapsae/Xenorhabdus nematophila are mass produced for use as biological insecticides. Two geographically distinct strains of each bacterial species were isolated from their nematode partners and serially subcultured on in vitro media to assess trait stability. Subculturing resulted in a phase shift to secondary forms in one P. luminescens strain and both X. nematophila strains within ten culture cycles. When phase shift was controlled changes in the P. luminescens strains were noted after 25 cycles in liquid culture including reductions in virulence, cell and inclusion body size, inclusion body prevalence, and culture pigments. Bacterial growth rate, however, was enhanced. Conversely, the X. nematophila strains were resistant to change, with no significant alteration of any trait when phase shift was controlled. In vitro producers of the P. luminescens/H. bacteriophora must consider the consequences of bacterial trait stability when designing their mass production processes.