Carbon Source Requirements for Exopolysaccharide Production by Lactobacillus casei CG11 and Partial Structure Analysis of the Polymer.

Exopolysaccharide production by Lactobacillus casei CG11 was studied in basal minimum medium containing various carbon sources (galactose, glucose, lactose, sucrose, maltose, melibiose) at concentrations of 2, 5, 10, and 20 g/liter. L. casei CG11 produced exopolysaccharides in basal minimum medium containing each of the sugars tested; lactose and galactose were the poorest carbon sources, and glucose was by far the most efficient carbon source. Sugar concentrations had a marked effect on polymer yield. Plasmid-cured Muc derivatives grew better in the presence of glucose and attained slightly higher populations than the wild-type strain. The values obtained with lactose were considerably lower for both growth and exopolysaccharide yield. The level of specific polymer production per cell obtained with glucose was distinctively lower for Muc derivatives than for the Muc strain. The polymer produced by L. casei CG11 in the presence of glucose was different from that formed in the presence of lactose. The polysaccharide produced by L. casei CG11 in basal minimum medium containing 20 g of glucose per liter had an intrinsic viscosity of 1.13 dl/g. It was rich in glucose (76%), which was present mostly as 2- or 3-linked residues along with some 2,3 doubly substituted glucose units, and in rhamnose (21%), which was present as 2-linked or terminal rhamnose; traces of mannose and galactose were also present.

Influence of Oxygen and pH on Methanethiol Production from l-Methionine by Brevibacterium linens CNRZ 918.

The effects of dissolved oxygen concentration and pH on the growth of Brevibacterium linens CNRZ 918 and its production of methanethiol from l-methionine were investigated. Optimal specific methanethiol production was obtained at 25% saturation of dissolved oxygen and at a pH between 8 and 9, whereas optimal cell growth occurred at 50% oxygen saturation and when the pH was maintained constantly at 7. Methanethiol production by nonproliferating bacteria required the presence of l-methionine (7 mM) in the culture medium. This was probably due to the induction of enzyme systems involved in the process. The intracellular concentration of l-methionine seemed to play a key role in this process. B. linens CNRZ 918 tolerated alkaline pHs with a maximal growth pH of approximately 9. Its orange pigmentation seemed to depend on the presence of l-methionine in the culture medium and on the concentration of dissolved oxygen.