Abstract: The actinomycete strain Y18 was isolated from ocean sediments collected from the Chukchi Sea in the Arctic Ocean. This actinomycete requires seawater for growth. Based on 16S rRNA sequence analysis, it belongs to the genus Nocardiopsis. Results of secondary-metabolite biosynthesis screening show that it contains polyethylene ketone type Ⅱ (PKSⅡ) and non ribosome-bound sulfur-containing peptide (NRPS) genes. It has antimicrobial activity against both Bacillus subtilis and Candida albicans. The optimal fermentation conditions of Y18 against Bacillus subtilis are as follows: fermentation medium containing peptone 2 g, casein hydrolysate 2 g, yeast extract 2 g, glucose 1 g, sea water 1 L, and seed liquid inoculum to 4%, an initial pH 8.0, a culture temperature of 28°C, a liquid volume of 20% in a 1 000 mL flask, and a fermentation time of 6 days. We found that antimicrobial activity remained stable with changes in heat, acid, alkali, and during storage at 4°C.

Key words: Marine actinomycetes, molecular identification, antibacterial activity, fermentation conditions, Arctic Ocean