Etiology of black-brown disease in cultured Caulerpa lentillifera

Abstract:

Caulerpa lentillifera is a seaweed species with increasing large-scale economic value due to its nutritional and health benefits. With the expansion of farming scale, problems associated with various diseases are becoming more common and severe. However, few research focusing on this topic have been published. In this study, the strain CL2017070801002 was isolated from C. lentillifera, which was diagnosed with black-brown disease in Dalian´s breeding farm. Following infection of healthy C. lentillifera with this strain at a concentration of 103~108 CFU/ml, each experimental group developed different black-brown lesions within 7 days. Under scanning electron microscopy, a large number of bacteria were accumulated on the cell surface of the alga, and the cells ruptured and died over time. These results indicated that CL201707070801002 was the causative pathogen of black-brown disease of C. lentillifera. Using gram staining as well as physiological and biochemical characteristics based on a 16S rDNA phylogenetic tree, the strain was identified as Vibrio alginolyticus. CL2017070801002 was highly sensitive to chloramphenicol, tetracycline, fleroxacin, doxycycline, and florfenicol; moderately sensitive to gentamicin and clarithromycin; and not sensitive to penicillin and cephalosporin. These results will provide useful information for the prevention and control of bacterial diseases of C. lentillifera.