Submitted to: Journal of Industrial Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/14/1998
Publication Date: N/A
Interpretive Summary: Control of unwanted grasses in turf is often unattainable with chemical herbicides. The use of specific microbial pathogens of weedy grasses offers a biological control alternative. Strains of the bacterium, Xanthomonas campestris, have been shown to selectively infect and kill annual bluegrass. The commercial use of this bioherbicide requires the development of low cost production methods which yield high concentrations of stable, effective bacterial cells. We have found that the bioherbicidal bacterium can be rapidly produced in liquid culture and, when harvested after growth had slowed, survived drying and storage at refrigerated temperatures. These results provide impetus for the further commercial development of this biocontrol agent.
Technical Abstract: Xanthomonas campestris MB245, a specific pathogen of the weedy grass Poa annua (annual bluegrass), is being developed as a bioherbicide to control this pest in turf. In this study, nutritional and environmental factors were evaluated based on their ability to support rapid submerged culture growth and high cell yield. Temperature optima for the growth of X. campestris cells in submerged culture were between 27 and 30 deg C. At a growth temperature of 30 deg C, optimal nutritional conditions for X. campestris growth supported generation times of 150-175 min and cell yields after 24 h growth of 1-2 x 10**10 cells/mL. Media containing sucrose or glucose as the carbon source and various organic nitrogen sources supported optimal X. campestris growth and cell yield. The addition of vitamin mixtures to complex and defined media had no significant effect on growth or cell yield. The age of X. campestris cultures had a significant impact on cell survival after freeze drying. Following freeze drying, log phase cell survival (44%) was significantly lower than early and late stationary phase cell survival, 62% and 68%, respectively. Cells harvested in stationary phase, freeze dried and stored under vacuum at 4 deg C, showed no significant loss in viability after 6 months. These studies have demonstrated that high cell concentrations of the bioherbicide, X. campestris, can be rapidly produced in submerged culture and stabilized as freeze dried preparations.