Isolation and screening of antibacterial and enzyme producing marine actinobacteria to approach probiotics against some pathogenic vibrios in shrimp Litopenaeus vannamei

The application of new probiotics is a good strategy in the biological control of infectious diseases in aquaculture. Approximately ۱۰۰ marine actinobacteria isolates were obtained from ۱۰ sediment samples of shrimp farms. Heat treatment of sediment samples resulted in a selective reduction of the non actinobacterial heterotrophic microflora. Starch nitrate agar medium exhibited more efficacy than glycerol arginine agar medium for isolation. Twenty seven percent of actinobacterial isolates showed antagonistic activities against pathogenic Vibrio spp. All the antagonistic isolates showed the typical morphology of genus Streptomyces. Exoenzymatic activity screening showed that ۴۴ %, ۲۶%, ۳۷% of antagonistic isolates represented amylase, lipase and protease activities, respectively. MNM-۱۴۰۰ strain exhibited highest antagonistic and exoenzymatic activity. The pathogenicity experiment revealed that MNM-۱۴۰۰ strain did not cause disease in Litopenaeus vannamei larvae. Extraction of produced antibacterial compounds by MNM-۱۴۰۰ strain showed that the active constituent didn’t have non polar property. Morphological, physiological and biochemical identification confirmed that MNM-۱۴۰۰ strain belonged to the genus streptomyces. Phylogenetic analysis by ۱۶S rRNA gene sequencing showed a high similarity between MNM-۱۴۰۰ strain and Streptomyces californicus (similarity: ۹۹%). These results suggest that the MNM-۱۴۰۰ strain can be considered as a potential probiotic in aquaculture

Keywords:

Probiotic , Marine actinobacteria , Biological control , Shrimp , Litopenaeus vannamei