Summary: Sporulation of Bacillus sphaericus, NCTC 7582, in a complex medium was strongly stimulated by growth in mixed culture with a sporing strain of B. cereus and with sporogenous and asporogenous strains of B. subtilis, NCTC 85. There was a similar, but less pronounced, effect with a variety of Gram-positive and Gram-negative organisms. The degree of sporulation of B. sphaericus in these mixed cultures depended on (a) an external stimulus from the medium and (b) the previous cultural history of the B. sphaericus inoculum upon which depended its ability to respond to the external stimulus. Sporulation of B. sphaericus in pure culture was strongly stimulated by bicarbonate and ketoglutarate, suggesting that increased carbon dioxide production was the stimulating factor in mixed cultures.
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