Distribution of Vibrio halioticoli around an Abalone-farming Center in Japan

Abstract

Vibrio halioticoli is the dominant bacterial species in the gut of abalone, Haliotis discus hannai. The bacterium may contribute to the digestion of seaweed, and form a symbiotic association with the host. However, the process by which the bacterium colonizes the gut of abalone is unknown and intriguing given the non-motile nature of V. halioticoli. To clarify the colonization process, the distribution of the bacterium in seawater, as well as the fecal material and diet of abalone was investigated at an abalone farm. Viable bacterial counts of V. halioticoli were determined in each sample using a colony hybridization technique specifically designed for the bacterium. The count in seawater and culture seawater was 3 CFU/ml. The number of V. halioticoli in a diatom bed used as a diet for juvenile abalone was 7.9×102 CFU/g. Fractionation of the diatom bed sample using 0.2 and 8.0-μm filters indicated that the viable count was higher in the attached fraction (3.4×102 CFU/g; >8.0 μm) than in free-living fraction (76 CFU/g; 0.2 μm-8.0 μm). Furthermore, viable V. halioticoli was estimated to be 3.6×103 CFU/g in the fecal material of juvenile abalone which had ingested diatoms, as compared to 1.2×105 CFU/g in that of juveniles fed on artificial diet. These results suggest that V. halioticoli cells in seawater and/or on diatoms contribute to the colonization of the gut in abalone. © 2002, Japanese Society of Microbial Ecology & The Japanese Society of Soil Microbiology. All rights reserved.