J Vandenberghe

Phenotypic diversity amongst Vibrio isolates from marine aquaculture systems

A total number of 1473 Vibrio isolates were collected from different aquaculture systems in many countries. Isolates were obtained from bivalves (mussels, scallops, oysters), shrimp and fish, sea urchins, live feed (algae, Artemia, rotifers), seaweed, aquaculture market products and from the aquaculture environment (tank water, seawater, sediments). Eggs, healthy and diseased or dead larvae, and adult organisms were sampled from cold-water species and moderate- to warm-water species. All isolates were phenotypically characterized using the Biolog GN technique. Eighty-nine different clusters were obtained, of these clusters, only 33 were identified comprehending 992 isolates. The remaining 56 groups did not cluster with any of the included type strains and remained unidentified. Seventy-eight isolates did not cluster with any other strain. It was shown that the Vibrio genus is a phenotypically diverse group making the identification with the Biolog system difficult and unreliable.

Vibrios associated with Penaeus chinensis (Crustacea: Decapoda) larvae in Chinese shrimp hatcheries

Bacteriological surveys were performed in 1995 and 1996 in three shrimp hatcheries located in the north of the Peoples Republic of China. Samples were taken from routine productions of healthy Penaeus chinensis larvae, their environment and from diseased larvae. A total of 186 isolates from the dominant bacterial flora was characterized by Biolog metabolic fingerprinting and identified by comparison to a database of 850 Vibrio type- and reference strains. Representative Vibrio harveyi strains were further genotypically analyzed by AFLP fingerprinting of whole-genomes. An overwhelming predominance of V. alginolyticus and V. harveyi was observed in the larval developmental stages from zoea stage on. The flora associated with larvae is not very stable and is influenced by the bacterial flora of the administered food and by the environment. In the 1995 survey, the bacterial flora of successful P. chinensis larvae productions was mainly dominated by V. alginolyticus and unidentified Gram negative strains, while V. harveyi was absent. The bacterial numbers gradually increased from nauplii stage to post-larval stage, but few vibrios were isolated from nauplii stage. High V. harveyi numbers (up to 105 CFU/larva) in the larvae are correlated with weak larvae and mass mortalities. Between V. harveyi strains, isolated from healthy and diseased larvae, no phenotypic or genotypic differences were found. The presence of V. alginolyticus might influence the pathogenicity of V. harveyi or might have an impact on the resistance of larvae to bacterial pathogens.

Selection of bacteria enhancing the growth rate of axenically hatched rotifers (Brachionus plicatilis).

Abstract The effect of bacterial strains on the growth rate of rotifers, Brachionus plicatilis , was determined under monoxenic conditions. The first objective was to obtain sterile rotifer cultures starting from rotifer resting eggs using merthiolate or glutaraldehyde as disinfectant. Sterile rotifer cultures were obtained, without affecting the hatching ability of the resting eggs, when 0.05 μl/l glutaraldehyde was used. This disinfection procedure was used to examine the effect of 20 bacterial strains, isolated from well-performing live-feed production systems, on the population growth rate of rotifers cultured under monoxenic conditions. Five out of the 20 bacterial strains tested were able to improve significantly the asexual reproduction of rotifers. The population growth rate ( μ pop ) of rotifer cultures treated with GR 12 and GR11 (respectively 0.664±0.043 and 0.622±0.062) was significantly higher than the μ pop of the control treatment (0.512±0.101). Overall, the egg ratio after 48 h was significantly higher in the cultures inoculated with the bacterial strains than in the axenic control treatment. The results show that it is possible to control the microbial community in rotifer cultures started from disinfected resting eggs by adding bacterial strains which have a positive effect on the population growth rate.