Libao Wang

Isolation and characterization of Vibrio metschnikovii causing infection in farmed Portunus trituberculatus in China

In August 2008, a massive epizootic occurred among Portunus trituberculatus reared together with Palaemon carincauda Holthuis and Sinonovacula constricta in the seawater pond of Ningang farm, Rudong district, Jiangsu province, China. The disease occurred in crabs from juveniles to adults, and the mortality rate reached 30–40%. The diseased crabs exhibited lethargy, hepatopancreas turgidity, and elevated levels of turbid hemolymph. A gram-negative, rod-shaped bacterium (designated as strain LGS-1) was isolated from the ascitic fluid of the diseased and moribund crabs and was confirmed as the causative agent by our infectivity study. We conducted morphological and biochemical characterization of LGS-1, and sequenced the 16S rRNA gene, which led us to identify the bacterium as Vibrio metschnikovii. Drug sensitivity tests showed that this pathogenic bacterium is sensitive to florfenicol, orfloxacin, and SXT, but completely resistant to antibacterial drugs like gentamicin, erythrocin, and acheomycin. This is the first report on Vibrio metschnikovii as a virulent pathogen for Portunus trituberculatus.

Optimization of hard clams, polychaetes, physical disturbance and denitrifying bacteria of removing nutrients in marine sediment

Marine organisms are known to play important roles in transforming nutrients in sediments, however, guidelines to optimize sediment restoration are not available. We conducted a laboratory mesocosm experiment to investigate the role of hard clams, polychaetes, the degree of physical disturbance and denitrifying bacterial concentrations in removing total nitrogen (TN), total phosphorus (TP), and total organic carbon (TOC) in marine sediments. Response surface methodology was employed to analyze the results of initial experiments and in a subsequent experiment identified optimal combinations of parameters. Balancing the TN, TP, TOC removal efficiency, our model predicted 39% TN removal, 33% TP removal, and 42% TOC removal for a 14-day laboratory bioremediation trial using hard clams biomass of 1.2kgm(-2), physical disturbance depth of 16.4cm, bacterial density of 0.18Lm(-2), and polychaetes biomass of 0.16kgm(-2), respectively. These results emphasize the value of combining different species in field-based bioremediation.

Multiple Pathogens Prevalent in Shrimp Penaeus vannamei Cultured from Greenhouse Ponds in Jiangsu Province of China

In recent years, several pathogens have emerged and caused heavy mortality in Asia. In this study, we investigated the prevalence of pathogens in specimens of whiteleg shrimp (Penaeus vannamei) collected from greenhouse ponds. In total, six pathogens were tested in these shrimp, three of which, including Enterocytozoon hepatopenaei (EHP), acute hepatopancreatic necrosis disease (AHPND)-causing Vibrio parahaemolyticus and infectious hypodermal and haematopoietic necrosis virus (IHHNV), were detected in shrimp aquaculture, with EHP being the most prevalent; Taura syndrome virus (TSV), White spot syndrome virus (WSSV) and yellow head virus (YHV) were not detected in these samples. Ultrastructure examination revealed the presence of a large number of EHP spores infecting hepatopancreatic epithelial cells of shrimp. Body weight (BW), body length (BL) and BW/BL ratio, revealed growth retardation among EHP-infected shrimp, as indicated by the significantly lower values of BW, BL and BW/BL ratio in these shrimps than those in EHP-uninfected shrimp (P<0.05). Together, these data indicated that EHP causes severe growth retardation of shrimp and is a major pathogen of aquacultured shrimp culturing in greenhouse ponds in Jiangsu Province; effective measures should be undertaken to control its spread.