Isolation and Identification of Antimicrobial Marine-Derived Actinomycetes from Bach Long Vi Island, Viet Nam

Actinomycetes, Gram-positive bacteria with high G + C contents in their DNA, are proven to be a good source of biologically active metabolites, especially since more than 50% of antibiotics used in clinical originated from actinobacteria. Bach Long Vi is the furthest off-shore, in-bay island of Vietnam, with the first national protective marine area of very high marine biodiversity, including actinobacteria. In the search for alternative local antibiotic producers, 30 marine-derived actinomycete strains were isolated from samples collected in the coastal water of Bach Long Vi in June 2022. Antimicrobial tests revealed that 28/30 isolated strains showed antimicrobial activities, of which 4/30 strains were active against at least 6/10 tested microorganisms, 11/30 strains were active against Gram-negative bacteria, and 15/30 strains were resistant to fungus with the MIC values ranged 16–256 µg/ml. The four most promising strains, G551, G566, G571 and G577, were identified as belonging to two genera, Nocardiopsis and Salinispora and their 16S rRNA gene sequences were registered in GenBank-NCBI with accession numbers of OP658869, OP658870, OP658871 and OP658872, respectively. The obtained result suggested that further study should be conducted on the chemical and biological characteristics of those four most promising strains.