Inhibition of shrimp pathogenic vibrios by extracellular compounds from a proteolytic bacterium Pseudomonas sp. W3

Pseudomonas sp. W3, a bacterium known to produce an extracellular alkaline protease, secreted secondary metabolites that inhibited pathogenic bacteria responsible for shrimp luminous vibriosis disease. Antivibrio compounds in the culture supernatant or culture filtrates (0.45 \ub5m and 0.22 \ub5m) of the isolate W3 were tested using an agar well diffusion method on a number of pathogenic vibrios. Vibrio harveyi PSU 2015 a pathogenic isolate was the most sensitive strain. The effectiveness of preparations from the isolate W3 against V. harveyi PSU 2015, and V. cholerae PSSCMI 0062 was in the order of culture supernatant > 0.45 \ub5m culture filtrate > 0.22 \ub5m culture filtrate. These extracellular antivibrio compounds also lysed both dead and living cells of V. harveyi PSU 2015. Results of the partial characterization tests indicated that there was some particulate antivibrio compound that was destroyed by treatment with enzymes particularly \u3b1-chymotrypsin, autoclaving at 121\ubaC for 15 min and was mostly removed by filtration through a 0.22 \ub5m filter. Most of the inhibitory compounds were of small molecular weight able to pass through a 0.22 \ub5m filter and were resistant to treatment with various enzymes, pH values between 4-8 and temperatures up to 121\ubaC for 30 min. The optimum pH for the antivibrio activity in the 0.45 \ub5m culture filtrate was between pH 6-7

Selection of proteolytic bacteria with ability to inhibit Vibrio harveyi during white shrimp (Litopenaeus vannamei) cultivation

Five isolates of bacteria with high proteolytic activity, isolated from water samples of intensive shrimp ponds in southern Thailand, were selected to test for the ability to control the shrimp pathogen Vibrioharveyi. 70 μl of each culture broth were investigated for their ability to inhibit V. harveyi using an agar well diffusion test but only one isolate W3 gave a reasonable sized inhibition zone of 21.62 mm. This zone wassimilar to that of oxolinic acid (2 μg) and sulfamethoxazole (25 μg). The W3 isolate was identified as Pseudomonas sp. Shrimp cultivation in aquaria was conducted to investigate the inhibition of V. harveyi bythe isolate W3. The experiment consisted of a treatment of the shrimp culture with an inoculum of the isolate W3 and V. harveyi (biocontrol set), a positive control set (only inoculation of V. harveyi) and a negativecontrol set as without inoculation. No mortality was found in the negative control. Shrimp mortality in the biocontrol set (33%) was lower than that in the positive control set (40%); however, it showed no significantdifference (p>0.05). The average numbers of V. harveyi over 12 days of the biocontrol set were lower than those in the positive control set by about 1 log cycle although the numbers were not significantly different(p>0.05). The shrimp growth rate at day 32 of cultivation was in order of the biocontrol treatment (10.17%) > the negative control treatment (9.44%) > the positive control set (9.28%), but no significant difference (p>0.05) was observed among treatments

Inhibition of shrimp pathogenic vibrios by extracellular compounds from a proteolytic bacterium Pseudomonas sp. W3

Pseudomonas sp. W3, a bacterium known to produce an extracellular alkaline protease, secreted secondary metabolites that inhibited pathogenic bacteria responsible for shrimp luminous vibriosis disease. Antivibrio compounds in the culture supernatant or culture filtrates (0.45 µm and 0.22 µm) of the isolate W3 were tested using an agar well diffusion method on a number of pathogenic vibrios. Vibrio harveyi PSU 2015 a pathogenic isolate was the most sensitive strain. The effectiveness of preparations from the isolate W3 against V. harveyi PSU 2015, and V. cholerae PSSCMI 0062 was in the order of culture supernatant > 0.45 µm culture filtrate > 0.22 µm culture filtrate. These extracellular antivibrio compounds also lysed both dead and living cells of V. harveyi PSU 2015. Results of the partial characterization tests indicated that there was some particulate antivibrio compound that was destroyed by treatment with enzymes particularly α-chymotrypsin, autoclaving at 121ºC for 15 min and was mostly removed by filtration through a 0.22 µm filter. Most of the inhibitory compounds were of small molecular weight able to pass through a 0.22 µm filter and were resistant to treatment with various enzymes, pH values between 4-8 and temperatures up to 121ºC for 30 min. The optimum pH for the antivibrio activity in the 0.45 µm culture filtrate was between pH 6-7