The bulk DNA in bleomycin-sensitive ascites hepatoma, AH66, was more susceptible to single strand scission by this antibiotic than that in the resistant AH66F cells. The break was repairable in the resistant cells, while it was incompletely repaired in the sensitive cells. Rejoining was inhibited by actinomycin D but not by cycloheximide. The sedimentation coefficient of bulk DNA was reduced with increasing lysis time of the cells in alkali-sodium dodecyl sulfate before sucrose gradient centrifugation, while that of damaged DNA in bleomycin-treated cells did not change further under the same conditions. This suggests induction of breakage by the antibiotic of an alkali-labile linkage in the chromosomal DNA.
A new antibiotic, designated SS-56 C, has been isolated from a culture broth of Streptomyces eurocidicus No. SS-56. The antibiotic is active against a number of Gram-positive, negative bacteria and fungi. Structural studies including analysis of NMR and in particular MS spectra and acid degradation suggested that SS-56 C substance is the 2-hydroxy derivative of A-396-I substance. Together with SS-56 C substance, were isolated two new hexoglycosides of 2-deoxystreptamine (SS-56 A and B), as well as A-396-I substance (SS-56 D), and gross structures were deduced.
In a previous paper1) we reported that Bacillus circulans, strain No. YQW-B6, produced a complex of aminoglycoside antibiotics designated Bu-1709, of which the two major components, A1 and A2, were identified as butirosins A and B2). Two additional components, E1 and E2, have now been isolated and characterized. They have antibacterial spectra similar to the butirosins but with substantially less intrinsic activity. Bu-1709 E1 and E2 contain the paromamine moiety in place of the neamine moiety of the butirosins.