Characterization and bioprospecting of endophytic Actinomycetota from the leaves of the seagrasses Thalassia hemprichii and Syringodium isoetifolium

Bacteria of the phylum Actinomycetota are renowned for producing numerous bioactive compounds. Prior research has focused on terrestrial strains, rather than those from marine environments. This study aimed to isolate and characterize endophytic Actinomycetota bacterial strains from the leaves of the seagrasses Thalassia hemprichii and Syringodium isoetifolium from the coast of Tanzania, to analyze their bioactive metabolites against pathogenic micro-organisms. Fourteen isolates belonging to the genera Rhodococcus, Brachybacterium, Microbacterium, Kocuria, Gordonia, Janibacter, Flavobacterium, Nocardioides, Cellulosimicrobium, Leifsonia and Streptomyces were identified based on morphological and biochemical analysis, and partial 16S rRNA gene sequences. Among these, six putative novel species are reported. Most of the crude extracts demonstrated antimicrobial activity against at least one of Staphylococcus aureus, Pseudomonas aeruginosa, Escherichia coli and Candida albicans. Strains of Microbacterium (SID3), Streptomyces (THD8), and Cellulosimicrobium (SID1) were active against all the tested human pathogens with inhibition zones ranging from 11 to 32 mm. Ten Actinomycetota species exhibited potential for toxic activities. Endophytic Actinomycetota associated with the two studied seagrass species hold significant biotechnological potential for producing biologically active compounds.