Bioactive compound from marine seagrass Streptomyces argenteolus TMA13: combatting fish pathogens with time-kill kinetics and live-dead cell imaging

• Published in: Brazilian journal of microbiology 2024-09, Vol.55 (3), p.2669-2681
• Main Authors: Elumalai, Lokesh, Nagarajan, Siddharthan, Anbalmani, Sivarajan, Murthy, Sangeetha, Manikkam, Radhakrishnan, Ramasamy, Balagurunathan
• Format: Article
• Language: English
• Subjects: Animals; Anti-Bacterial Agents - pharmacology; Antibacterial activity; Antiinfectives and antibacterials; Aquatic environment; Assaying; Bacteria; Bioactive compounds; Biofilms; Biofilms - drug effects; Biomedical and Life Sciences; Carbon sources; Cell death; Cell differentiation; Cell viability; Differentiation (biology); Effectiveness; Fish; Fish Diseases - microbiology; Fishes - microbiology; Fluorescence; Fluorescence in situ hybridization; Food Microbiology; Functional groups; Kinetics; Life Sciences; Low concentrations; Medical Microbiology; Medicine and Public Health - Research Paper; Metabolites; Microbial Ecology; Microbial Genetics and Genomics; Microbial Sensitivity Tests; Microbiology; Mycology; Pathogens; Sea grasses; Secondary metabolites; Streptomyces; Streptomyces - chemistry; Streptomyces - metabolism; Terrestrial environments; Vibrio - drug effects
• ISSN: 1517-8382; 1678-4405; 1678-4405
• DOI: 10.1007/s42770-024-01407-w

Actinobacteria, pervasive in aquatic and terrestrial environments, exhibit a filamentous morphology, possess DNA with a specific G + C content and production of numerous secondary metabolites. This study, focused on actinobacteria isolated from marine seagrass, investigating their antibacterial activity against fish pathogens. Among 28 isolates, Streptomyces argenteolus TMA13 displayed the maximum zone of inhibition against fish pathogens— Aeromonas hydrophila (10 mm), Aeromonas caviae (22 mm), Edwardsiella tarda (17 mm), Vibrio harveyi (22 mm) and Vibrio anguillarum (12 mm) using the agar plug method. Optimization of this potent strain involved with various factors, including pH, temperature, carbon source and salt condition to enhance both yield production and antibacterial efficacy. In anti-biofilm assay shows the maximum percentage of inhibition while increasing concentration of TMA13 extract. Minimal Inhibitory Concentration (MIC) and Minimal Bactericidal Concentration (MBC) assays with TMA13 crude extract demonstrated potent activity against fish pathogens at remarkably low concentrations. Time-kill kinetics assay showcased growth curve variations over different time intervals for all fish pathogens treated with a 100 µg/ml concentration of crude extract, indicating a decline in cells viability and progression into the death phase. Additionally, fluorescence microscopic visualization of bacterial cells exposed to the extracts emitting green and red fluorescence, enabling live-dead cell differentiation was also studied. Further characterization of the crude extract through GC–MS and FT-IR analyses performed and identified secondary metabolites with functional groups exhibiting significant antibacterial activity. This study elucidates the capacity of Streptomyces argenteolus TMA13 to enhance the production of antibiotic compounds effective against fish pathogens.