| Probiotic Halomonas sp. with high denitrification activity, Pseudoalteromonas sp. antagonism against vibrio and a Bacillus sp. were isolated from shrimp ponds. Bacillus sp. combining carbon source was added to the biofloc shrimp pond system and the effect were analyzed. The nutrition of biofloc was evaluated by feeding nereis pelagica and artemia saline with biofloc. The main results were as follows:1 Isolation and identification of a Bacillus sp. and application in bioflocs technology shrimp culture systemA strain was isolated from a shrimp pond and designated as 2013042402 (Strain 02). Both 16S rDNA sequencing and gas chromatographic analysis of whole cell fatty acids indicated that strain 02 was a Bacillus sp.. In order to investigate the function of strain 02 used in bioflocs technology (BFT) shrimp culture system, strain 02 (2.0×10 CFU/mL) joint with sucrose (70% of feed), strain 02 and sucrose were added to the shrimp cultured system respectively. Investigations on the effect of strain 02 on water physicochemical parameter (pH, ammonia-N and nitrite-N), shrimp growth, survival rate and composition of predominant bacterial communities in water body was conducted. The results indicated that the strain 02 joint with sucrose could significantly reduce the concentrations of ammonia-N and nitrite-N of aquaculture water body, improve the shrimp survival rate. Strain 02 added to the bioflocs shrimp farming systems could optimize the structure of bacterial communities and inhibit the growth of vibrio.2 Optimization of fermentation medium for a Bacillus sp.Corn flour, wheat bran, brown sugar, soybean meal, peanut meal, and urea were used as raw materials to ferment Bacillus sp.. The best component of fermentation medium was screened through the C/N ratio. Fermentation medium and conditions were optimized through the single factor and orthogonal test. The optimal composition of medium for Bacillus sp. were corn flour 20 g/L, brown sugar 20 g/L, soybean meal powder 9 g/L; the optimal fermentation conditions was under the liquid loading rate of 0.3, initial pH 7.0, temperature of 31℃; the results of growth curve showed that 54h is the best time for collecting Bacillus sp. when the baterial concentration was at 2.83 X 109 cfu/mL and 78h is the best time for collecting spores with concentraton at 7.07 X 108 cfu/mL. Optimization of fermentation medium for Bacillus sp. might reduce cost, increase dencity of living bacterium. The investigation above may give the guidance for the application of Bacillus sp. in aquaculture.3 Isolation and characterization of a bacterial strain with high denitrification activity from shrimp pondsA bacterial strain with high denitrification activity was isolated from a shrimp pond and designated as 2013092004 (referred to as strain 04). Sucrose, sodium succinate, glucose, sodium citrate and soluble starch were used to determine the effects of carbon source on the denitrifying efficacy of strain 04. We also used sucrose as carbon source and ammonia as nitrogen source to determine the effect of C/N, pH and salinity on the denitrifying efficacy. The effect of ammonia concentration and nitrite concentration on the denitrifying efficacy was studied. Our results showed that maximal denitrifying efficacy was achieved under the condition of sucrose being used as the carbon source, C/N>15, initial pH7-9, and the salinity of 5-45. The 24h-denitrifying rate was 100% for ammonia at the concentration of 30mg/L and 89% for nitrite at the concentration of 40mg/L. Challenge studies showed that LD50 of strain 04 was 1000-fold lower than that of Vibrio harveyi, a known pathogen for shrimp. Gas chromatography of bacterial whole cell fatty acids and 16S rDNA sequence analysis indicated that strain 04 was classified as Halomonas sp. These studies provide scientific foundation for its agricultural application.4 Isolation and identification of a bacterial strain with vibrios-antagonism from shrimp pondsA strain was isolated from a shrimp pond and designated as 2013082515 (Strain 15). The antibacterial effect and minimum antibacterial concentrations of strain 15 were analyzed using Vibrio, anguillarum, V. harveyi and V. parahaemolyticus as indicator bacteria. At the same time, the antibacterial effect of strain 15 against other seven marine vibrios including V. vulnificus, V. alginolyticus, V. diabolicus, V. campbellii, V. natriegens, V. brasiliensis and V. rotiferianus was analyzed. The results showed that strain 15 had obvious antibacterial effect on three indicator bacteria. The minimal inhibitory concentrations of strain 15 on V. anguillarum, V. harveyi and V. parahaemolyticus were 2.5x104 CFU/mL,2.5×105 CFU/mL,2.5×105 CFU/mL respectively, and antibacterial effect of strain 15 against other 7 vibrios were proved with different effect. Biological safety evaluation test on strain 15 used as probiotic was conducted by injection and immersion challenge. The result showed that strain 15 at high concentrations (injection challenge 1.84×107CFU/mL, immersion challenge 4.17×107CFU/mL) had potential toxicity to shrimp. Both gas chromatographic analysis of bacterial whole cell fatty acids and 16S rDNA sequencing indicated that Strain 15 was a Pseudoalteromonas sp.5 Reuse of floccules from a biofloc shrimp pondThe nutrition of biofloc was evaluated from the aspects of survival rate and weight in the experiment of feeding nereis pelagica and artemia saline with biofloc. About nereis pelagica, survival rate of floc group is higher than bait group, and significantly higher than control group; average weight of floc group is lower than bait group, but significantly higher than control group. About artemia saline, survival rate of floc group is significantly higher than bait group and control group. Thus, there are certain effect on feeding nereis pelagica and artemia saline with biofloc. These studies provide scientific foundation for the recycling of floccules. |
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