Bioactive pigment production by marine bacteria from Colombian estuarine and deep–sea environments

The marine environment is a reservoir of microbial diversity with high biotechnological potential. Natural pigments, such as some secondary metabolites, are of particular interest due to their ease of microbial cultivation and recovery, as well as their diverse biological activities. This study aimed to explore pigment production by bacteria isolated from estuarine and deep-sea environments in Colombia and evaluate their antimicrobial potential. Six from twenty-six isolates were tested for pigment production, and were taxonomically assigned to the genera Streptomyces (four), Pseudomonas (one), and Serratia (one). The pigment extracts demonstrated strong antimicrobial activity, with inhibition exceeding 90% against Methicillin-resistant Staphylococcus aureus (MRSA) and Candida albicans. Streptomyces sp. INV ACT17, isolated from marine sediments at 1,400 m depth was the most promising strain. Further characterization identified ISP-2 medium with a 1.5 mg/mL inoculum as optimal for pigment production. FTIR and molecular network dereplication analysis using UHPLC-MS/MS suggested actinomycin D as the major pigmented compound, a finding subsequently confirmed by NMR spectroscopy. Kinetic studies revealed a non-growth-associated profile with maximum production (762 ± 59 mg/L) after 196 h, and achieved a IC50 0.12 µg/mL against MRSA. These findings highlight deep–sea actinobacteria as valuable sources of bioactive pigments and establish Streptomyces sp. INV ACT17 is a promising candidate for natural antimicrobial discovery and development.