OPTIMIZATION OF A CHEMICALLY-DEFINED, MINIMAL MEDIUM FOR CLOSTRIDIUM-THERMOSACCHAROLYTICUM

This article presents results from a systematic study aimed at formulating a defined, minimal medium for the growth of Clostridium thermosaccharolyticum in batch and in continuous culture. At least one vitamin appears to be essential, and there is no demonstrable requirement for trace minerals. The defined medium is shown to support growth on high substrate concentrations with scaled nutrient levels and is expected to permit complete utilization when nutrient limitation(s) are overcome. The observed elemental requirements are compared with cell mass fraction measurements and with a typical cell composition. The maximum growth rate (mu(max)) for batch growth of C. thermosaccharolyticum on the minimal medium is 0.27 h(-1) as compared with values of similar to 0.4 h(-1) typically reported for growth on complex media. However, exponential growth terminates at an optical density of about 0.22 corresponding to about 40% of the final value attained. Greater understanding of nutrient requirements and interactions is needed to address this issue.