Physiology of Growth and Sporulation in Bacillus cereus I. Effect of Glutamic and Other Amino Acids

Abstract

Buono , F. (Syracuse University, Syracuse, N.Y.), R. Testa, and D. G. Lundgren . Physiology of growth and sporulation in Bacillus cereus . I. Effect of glutamic and other amino acids. J. Bacteriol. 91: 2291–2299. 1966.—Growth and sporulation were studied in Bacillus cereus by use of an active culture technique and a synthetic medium. A high level of glutamic acid (70 m m ) was required for optimal growth and glucose oxidation followed by sporulation even though relatively little glutamic acid was consumed (14 m m ). Optimal growth occurred with a combination of 14 m m glutamic acid and 56 m m (NH 4 ) 2 SO 4 , aspartic acid, or alanine. Ornithine or arginine at 70 m m could replace glutamic acid in the synthetic medium without affecting the normal growth cycle. Glutamic acid was not replaced by any other amino acid, by (NH 4 ) 2 SO 4 , or by a combination of either α-ketoglutarate or pyruvate plus (NH 4 ) 2 SO 4 . Enzyme assays of cell-free extracts prepared from cells harvested at different times were used to study the metabolism of glutamic acid. Glutamic-oxaloacetic and glutamic-pyruvate transaminases were completely activated (or derepressed) during early stages of sporulation (period of 6 to 8 hr). Alanine dehydrogenase responded in a similar manner, but the levels of this enzyme were much higher throughout the culture cycle. Neither glutamic dehydrogenase nor α-ketoglutarate dehydrogenase was detected. Sporulation in a replacement salts medium was studied with cells harvested at different times from the synthetic medium. Cultures 2 to 6 hr old were unable to sporulate in the replacement salts medium unless glutamic acid (7.0 m m ) was present. By the 6th hr, cells were in the early stages of sporulation, showing spore septa development. Cultures 8 hr old sporulated in the replacement salts medium. Other metabolic intermediates able to replace glutamic acid in the replacement salts medium were alanine, aspartic acid, and glutamine at equimolar concentrations. Also, ammonium ions in combination with pyruvic, oxaloacetic, α-ketoglutaric, or fumaric acid replaced glutamic acid. The likely role of these metabolites is discussed.