A new peptide antibiotic complex, B-43, active against Gram-positive and Gram-negative bacteria, was isolated from a strain of Bacillus circulans. This antibiotic contains aspartic acid, valine, isoleucine, leucine, phenylalanine and 2, 4-diaminobutyric acid. It seems to be related to polypeptin and antibiotic complex 4205, but differs in that it contains aspartic acid residue.
