|Shapiro Ilan, David|
Submitted to: International Journal of Nematology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/31/2005
Publication Date: 12/15/2005
Citation: Bai, C., Shapiro Ilan, D.I., Wang, Y., Gaugler, R., Crowles, E.A., Yi, S. 2005. Protein changes in the symbiotic bacterium Photorhabdus luminescens during in vitro serial culture. International Journal of Nematology. 15:126-135. Interpretive Summary: Nematodes are small round worms. Some nematodes effectively kill insect pests. They kill insect pests with the help of bacteria that live inside the nematode. The quality of the bacteria directly influences the killing power of the nematode. It is conceivable that the nematodes or their bacteria could experience detrimental change when these organisms are repeatedly cultured for laboratory or industrial purposes. We investigated changes in the bacteria's proteins during repeated culture. Substantial changes during culturing were found in two strains of a bacterial species. Analysis indicated that the proteins that changed were likely direct contributors to the killing power of the nematode-bacteria team, such as toxin proteins; enzymes and cell membrane proteins. These proteins might be used in genetic improvement to enhance the insecticidal function of the nematodes.
Technical Abstract: Heterorhabditid nematodes kill their hosts with the aid of symbiotic bacteria (Photorhabdus spp.) that are carried within the intestines of nematode. The stability of the bacteria in serial culture is essential for maintaining virulence and success in mass production. Photorhabdus bacteria exist as two variant forms, phase I and phase II; the former is generally more desirable for culture purposes. We investigated changes in total protein electrophoresis diagrams during 21 in vitro culture cycles of P. luminescens strains HB-GA and HB-NJ 21. Substantial changes for both strains were observed in protein arrays after 21 culture cycles; the protein alterations were observed in both variant forms of the bacteria (phase I and phase II). The level of change appeared to increase as the number of cultural cycles increased. At least three observed protein changes were common to both the HB-NJ and HB-GA strains. A search on protein sequence similarity revealed that the majority of protein changes in strain HB-GA are likely related to biologically active proteins including a paralyzed flagella protein, an insecticidal toxin and insecticidal toxin complex protein TccC1, catalyzing enzymes including a protease (that also contributes to insect death), an alkaline phosphatase, an allene oxide cyclase-like enzyme (early-response to dehydration protein), a Holliday junction DNA helicase, and membrane proteins such as an outer membrane fimbrial usher protein. The observed protein variations indicate that genetic changes during in vitro serial culture could affect traits critical to the bacterial virulence and survival capacity.