Effects of glutamic acid on sporulation of Bacillus cereus and on spore properties

Abstract

The effects of glutamic acid on growth, sporulation, and properties of Bacillus cereus spores were studied using a glutamic acid – glucose – glycine – yeast extract medium (+GA +YE) and a medium in which five amino acids were substituted for yeast extract (+GA +AA). In the +GA +YE medium, glucose and glycine were used principally during vegetative growth but glutamic acid was used during growth and sporulation. Omission of glutamic acid from either medium (−GA +YE or −GA +AA) reduced the percentage of the final population which was heat resistant. The resistance of the spore populations decreased as the complexity of the medium decreased (+GA +YE > −GA +YE > +GA +AA > −GA +AA). All four media supported 90+% sporulation, but total cell yield decreased and the time required for growth and sporulation increased as the complexity of the medium decreased. The most heat-resistant populations contained the least DPA per spore and had the highest Ca:DPA ratio. Spores from glutamic acid deficient medium (−GA +YE) were less resistant to ultraviolet radiation (uv.) than spores from +GA +YE medium. Glutamic acid deficiency in either medium did not influence refractility, calcium content, phase brightness, or phenol sensitivity of spores produced. Growth and sporulation were followed and spore properties were examined from cultures initiated in −GA +YE medium and supplemented with glutamic acid at specific times during the cycle of growth and sporulation. Glutamic acid was not used for organic acid production during vegetative growth but contributed to poly-β-hydroxybutyrate production, and it was used for vegetative growth. Glutamic acid was required in the medium before or during septum development for acquisition of maximum uv. resistance, and was required in the medium before or during forespore and cortex formation to influence DPA content and heat resistance.