Production of an autoinhibitor by a thermophilic bacillus.

Premature cessation of rapid, exponential growth and a low final cell yield were observed with a thermophilic bacillus in a glucose-mineral salts-vitamin medium. Restricted growth was not due to nutrient or oxygen limitation, to depressed pH, or to the physical effects of "crowding." Glucose conversion to cellular material was efficient at a low glucose charge (0.1%), but decreased with increasing concentrations of glucose. The likelihood that an autoinhibitor(s) was being produced was considered. Further studies revealed that an autoinhibitor appeared in the culture supernatant fluid at the end of the exponential phase. The factor was soluble in 75% ethanol which precipitated a large amount of extracellular slime. The crude inhibitor in the alcohol filtrate was dialyzable and withstood 3 hr of incubation at pH 2 or 12, and 30 min of boiling.