Antimicrobial compounds of an actinomycete derived from mangrove sediments

Mangrove-derived microorganism is a promising and important resource of novel natural products and lead compounds for drug discovery. This study aimed to find microbial secondary metabolites with novel structures. Based on the bioactive-guided screening of mangrove-derived actinomycetes, Streptomyces sp. GP3T5 was studied owing to its antibacterial, antibiofilm and anti-fungi activities. Three compounds (1-3) were isolated from the fermentation broth by organic solvent extraction, reversed-phase chromatography, Sephadex LH20 gel chromatography, and preparative high-performance liquid chromatography. Their structures were identified as pyrisulfoxin A (compound 1), collismycin A (compound 2), and echinomycin A (compound 3), respectively, via high resolution electrospray ionization mass spectroscopy (HRESIMS), nuclear magnetic resonance (NMR), ultraviolet (UV) spectroscopy. The activity evaluation of compounds 1-3 revealed that all three compounds showed antibacterial and antibiofilm activities. Compound 3 showed potent antibacterial activity against foodborne pathogens with minimum inhibitory concentrations (ρMIC) of 0.06 μg/mL for Listeria monocytogenes and Streptococcus agalactiae. The minimum biofilm inhibitory concentrations (ρMBIC) of compounds 1-3 against Acinetobacter baumannii were 32 μg/mL, 16 μg/mL, and 1 μg/mL, respectively. Compounds 2 and 3 showed good antifungal activity against plant pathogenic fungi, with half maximal inhibitory concentrations (IC50) ≤ 10 μg/mL and ≤ 1 μg/mL, respectively. In conclusion, these results on strain GP3T5 derived from mangroves provide valuable insights for further exploration of bioactive compounds from mangrove soil microorganisms.