Bacillus circulans, circulin

The peptide circulin, which was isolated from a culture of Bacillus circulans (431) should be placed in the polymyxin group. This antibiotic, active preferentially on Gram-negative bacteria (430) is a cyclic, basic heteromeric peptide, containing, as do polymyxins, L-a,7-diaminobutyric acid, threonine, and an optically active isomer of pelargonic acid which is probably (-b)6-methyloctanoic acid. In addition, circulin contains D-leucine (458). The composition (Table IX) of circulin is close to that of polymyxins A and E. However, this antibiotic, unlike polymyxin A, is inactivated by the enzyme lipase (458). Paper chromatography (173) distinguishes circulin from polymyxins A and E. 

Bacillus circulans strain Purdue Q19 was grown at 24 in shaken cultures in a basal medium containing dried brewer s yeast (2%), CaCOg (0.8%), (NH4)2S04 (0.5%), KCl (0.4%), and KH2PO4 (0.02%). Circulin activity was measured in the culture fluid after 3 days (from Murray et al., 1948). 

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