Evaluation of the Gulf of California as a potential source of bioactive marine actinobacteria

Actinobacteria produce many bioactive compounds currently used as antibiotics and anticancer drugs. The objective of this project was to evaluate the Gulf of California as a novel source of bioactive actinobacterial strains. A total of 235 actinobacterial strains were isolated from marine sediment collected in Concepción and los Ángeles bays (Mexico). Based on their morphology, seawater requirements, and 16S rRNA sequencing, actinobacterial strains were classified as Streptomyces, Micromonospora, and Salinispora. Sixty-nine organic and aqueous extracts were obtained using liquid-liquid extraction with ethyl acetate; 17 showed cytotoxic activity against breast cancer cells (MCF7) and cervical cancer cells (HeLa). The highest activity values observed, expressed as survival percentage, were 20–25% against MCF7 cells (strains S-365, S-355, and S-361) and 24–25% against HeLa cells (strains S-165, S-361, and S-353). Only three aqueous extracts showed antibiotic activity towards methicillin-resistant Staphylococcus aureus, with activity values of 3% and 6% for strains S-370 and S-369, respectively. Molecular weights found by liquid chromatography-mass spectrometry analysis are reported for Micromonospora species isolated from soil, but no species specific secondary metabolite evidence was observed for Salinispora isolates. The biological activity observed in this work offers opportunities for further chemical studies to define the compounds responsible for this activity in order to contribute to the discovery of new drugs and to acknowledge the Gulf of California as a reservoir of marine bioactive actinobacteria strains that are important for human health.