The aim of the present study was to isolate and identify marine actinomycetes to be used as probiotics having antibacterial activities. The actinomycete isolate YSCl2334 was isolated from Salwa beach in Jazan province, KSA. The isolate was screened for its potential to generate antimicrobial activity against the marine fish pathogens Tenacibaculum maritimum, Vibrio alginolyticus. The actinomycetes isolate YSCl2334 showed high antimicrobial activity against T. maritimum and no antimicrobial activity was observed against Vibrio alginolyticus. Also, the isolate YSCl2334 inhibited the growth of Gram-positive bacteria such Bacillus subtilis and Staphylococcus aureus and Gram-negative bacteria like Escherichia coli and Pseudomonas aeruginosa. The isolate did not show any activity against filamentous fungi like Aspergillus niger or A. flavus, although a strong antimicrobial activity was observed against unicellular fungi Candida albicans. The culture and physiological characteristics tests identified the actinomycetes isolate YSCl2334 as a member of the genus Nocardiopsis. The nucleotide sequence of the 16S rRNA gene (1.272 kb) of the identified isolate proved a 94% similarity with Nocardiopsis dassonvillei subsp. dassonvillei DSM 43111.
Key words: Marine actinomycetes, Nocardiopsis, Tenacibaculum maritimum, fish, Marine aquaculture