Bacicyclin, a new antibacterial cyclic hexapeptide from Bacillus sp. strain BC028 isolated from Mytilus edulis

[Display omitted] •A new cyclic hexapeptide (cyclo-(Gly-l-Leu-l-Val-l-IIe-d-Ala-d-Phe)) was detected.•Bacicyclin inhibits Gram-positive bacterial strains causing severe diseases.•Analogs of bacicyclin might be designed to increase antibiotic efficacy. A new cyclic hexapeptide, cyclo-(Gly-Leu-Val-IIe-Ala-Phe), named bacicyclin (1), was isolated from a marine Bacillus sp. strain associated with Mytilus edulis. The sequences of the amino acid building blocks of the cyclic peptide and its structure were determined by 1D- and 2D-NMR techniques. Marfey’s analysis showed that the amino acid building blocks had L-configuration in all cases except for alanine and phenylalanine, which had D-configuration. Bacicyclin (1) exhibited antibacterial activity against the clinically relevant strains Enterococcus faecalis and Staphylococcus aureus with minimal inhibitory concentration values of 8 and 12 µM, respectively. These results demonstrate the potential of marine bacteria as a promising source for the discovery of new antibiotics.