| dc.description.abstract | Probiotic bacteria for biocontrol of vibriosis were isolated from tiger shrimp larvae and hatchery environment. Almost all probiotic isolates could inhibit the growth of pathogenic Vibrio harveyi. SKT-b isolate from SkeIetonema was very effective in inhibiting V, harveyi and significantly reduced larval mortality in pathogen challenge assays. These prospective probiotic bacteria, at concentration 10'-10~ CFU/ml, did not show pathogenicity to shrimp larvae. SKT-b was Gram negative, short rod shape, exhibited yellow colonies an TCBS and swarming an SWC-agar media, motile, utilized glucose and sucrose but not lactose; produced extmcellular protease ancl amylase, but did not produce &itinasen Partial sequencing of 16s-rRMA gene showed that SKT-b was similar to Vib* algindyticus. To analyse mechanism of tiisease suppression by SKT-b, especially on their competition for adhesion sites, we constructed recombinant V. herveyi carrying gfp gene as a rnokufar marker. V. harvayi carrying gfp don& in a broad-host range plasmid (pWGO1) resulted in green-fluarescent colonies and cells due to the production of GFP, Growth cuwe analysis and pathogenicity assays showed that the recombinant V. Harveyi exhibited similar growth profiles as the wild type parental strain and did not show alteration in their pathogenicity. However, under nun selective long-term experiments without antibiotic pressure, pWGO? was not staMy maintained in any V. harveyi strains used in this study. Therefore we canstructed a mini Tn5 and TnIO transpuson containing gfp gene to be inserted into V. hatveyfs genamic DNA to yield stable transcanjugants. Tn5 transposition in V. harvejli strains did nut yield any transcanjugants, although we could obtain relatively trigti (10~t)r ansmjugans employing Tn10. One uf Tn 10 derived isolate of V, harvoyi G3 ((33-Tnf Ogfp) showed gfp expression and was further employed for adherence assay. Fluorescent G3-TnPOgfp cells could be obwwed inside the digestive tract of shrimp lanrae and fts population with SKT-b treatment was lower than without pmbiatic, demonstrating possible cornpetitiun for adherence sites or nutrition between V. harvsyi and SKY-b. ltrtroduction of SWb into shrimp tame through SKT-Mnriched Ademr'a resulted in higher growth rate than the mtro | id |
