Micrococcin P1

A new thiopeptide (micrococcin P3,1) and a known one (micrococcin P1,2) were isolated from the culture broth of a marine-derived strain ofBacillus stratosphericus. The structures of both compounds were elucidated using spectroscopic methods, including extensive 1D and 2D NMR analysis, high resolution mass spectrometry (HRMS), and tandem mass spectrometry. Both compounds exhibited potent antibacterial activities against Gram-positive strains with minimum inhibitory concentration (MIC) values of 0.05-0.8 μg/mL and did not show cytotoxicity in the MTT assay up to a concentration of 10 μM. This study adds a new promising member, micrococcin P3, to the family of thiopeptide antibiotics, which shows potential for the development of new antibiotics targeting Gram-positive bacteria.

Epibiotic bacteria associated with the filamentous marine cyanobacteriumMoorea producenswere explored as a novel source of antibiotics and to establish whether they can produce cyclodepsipeptides on their own. Here, we report the isolation of micrococcin P1 (1) (C48H49N13O9S6; obs.m/z1144.21930/572.60381) and micrococcin P2 (2) (C48H47N13O9S6; obs.m/z1142.20446/571.60370) from a strain ofBacillus marisflaviisolated fromM. producens' filaments. Interestingly, most bacteria isolated fromM. producens' filaments were found to be human pathogens. Stalked diatoms on the filaments suggested a possible terrestrial origin of some epibionts. CuSO4·5H2O assisted differential genomic DNA isolation and phylogenetic analysis showed that a Kenyan strain ofM. producensdiffered fromL. majusculastrain CCAP 1446/4 andL. majusculaclones. Organic extracts of the epibiotic bacteriaPseudoalteromonas carrageenovoraandOchrobactrum anthropidid not produce cyclodepsipeptides. Further characterization of 24 Firmicutes strains fromM. producensidentified extracts ofB. marisflavias most active. Our results showed that the genetic basis for synthesizing micrococcin P1 (1), discovered inBacillus cereusATCC 14579, is species/strain-dependent and this reinforces the need for molecular identification ofM. producensspecies worldwide and their epibionts. These findings indicate thatM. producens-associated bacteria are an overlooked source of antimicrobial compounds.

Thiopeptides are a class of potent antibiotics with promising therapeutic potential. We developed a novel Mo(vi)-oxide/picolinic acid catalyst for the cyclodehydration of cysteine peptides to form thiazoline heterocycles. With this powerful tool in hand, we completed the total syntheses of two representative thiopeptide antibiotics: micrococcin P1 and thiocillin I. These two concise syntheses (15 steps, longest linear sequence) feature a C-H activation strategy to install the trisubstituted pyridine core and thiazole groups. The synthetic material displays promising antimicrobial properties measured against a series of Gram-positive bacteria.