The Research On Microbial Community Ecology And The Screening Of Potential Probiotics In Tilapia Culture System

This paper investigated the amount of bacteria and the carbon metabolism of microbial communities in tilapia culture system by using plate count methods and Biolog ECO microplate, studied the correlation between microbial communities and environmental factors, and screened some potential probiotics which had high degradation ability from tilapia culture system, with the aim of tilapia healthy culture management. The results were shown as follows:1 Research on microbial community ecology in tilapia culture systemMicrobial communities in waters and sediments in four tilapia culture ponds (named 1#,2#,3# and 4#, respectively), which located in Shabei farm of New Generation Fishery Corporation in Panyu district of Guangzhou city, were investiged from May to October 2009. The results showed that the amount of bacteria and carbon metabolism of microbial communities in waters fluctuated more violently than in sediments in the whole farming periods. Microbial communities in waters were affected obviously by bacteriostatic drugs. The functional diversities of microbial communities in waters declined greatly in June, mainly related to the reduce of bacteria which used L-arginine, Glycyl-L-Glutamic acid, D,L-a-Glycerol phosphate,2-Hydroxy benzoic acid, and Putrescine as carbon sources. The amount of bacteria and the carbon metabolism of microbial communities in sediments maintained stable during the whole farming period and were affected little by bacteriostatic drugs. Microbial communities in waters and microbial communities in sediments had similarity on the utilization for the 31 kinds of carbon sources.Correlation between microbial communities and environmental factors in waters and sediments of tilapia culture ponds during May to October 2009 were studied by using Pearson correlation analysis. The results showed that the correlation between microbial communities and environment factors in waters was more obvious than that in sediments. In waters, significant negative correlation were observed between the amount of heterotrophic bacteria and pH, between the amount of heterotrophic bacteria and total organic carbon, between the amount of bacillus and total phosphorus, between carbon metabolism of microbial communities (including metabolic activities, functional diversities and the utilization for carbodrates and their derivatives, fatty acids and lipids, metabolic intermediates and secondary metabolites of microbial communities) and the contents of phosphate, and between the ulitization for metabolic intermediates and secondary metabolites of microbial communities and the levels of total phosphorus, while significant positive correlations were observed between the amount of bacillus and the levels of silicate, between functional diversities of microbial communities and the contents of nitrite, and between the utilization for metabolic intermediates and secondary metabolites of microbial communities and the contents of nitrite. In sediments, the correlations between all microbial community indices studied and total nitrogen, total phosphorus, sulphides, and organic matter were not significant.The amount of bacteria and carbon metabolism of microbial communities in waters, sediments and tilapia intestines in 1#,3# and 4# tilapia culture ponds were investigated at the final stock stage in November 2009. The results showed that carbon metabolism of microbial communities in waters and that in tilapia intestines were similar. The metabolic function of microbial communities in waters and intestines in pond 1# was significantly lower than that in pond 3# and pond 4#. The differences of carbon metabolism of microbial communities in sediments among pond 1#, pond 3# and pond 4# were not obvious.2 The screening of potecial probiotics in tilapia culture systemFifteen strains of enzyme-producing bacteria were screened from dominant bacteria isolated from tilapia culture system. Of the fifteen strains, these ten strains D30, D45, D50, D51, D53, D7, D11, D18, D21 and D55 had higher proteolytic activities, these nine strains D17, D11, D38, D41, D45, D47, D51, D52 and D55 had higher amylase activities. D51 and D53 had the highest proteolytic activities in all screened strains, and their proteolytic activities were both more than 70.0U/mL. D51 and D52 had the highest amylase activities in all screened strains and their amylase activities could be up to 267.86 U/mL and 190.52 U/mL, respectively. These four strains D11, D45, D51 and D55 both had high proteolytic activities and had high amylase activities. By using 16S rDNA identification, these five strains D50,D11, D18, D21 and D17 were identified as Bacillus sp., D45, D51, D52, D41, D47 and D53 were identified as Exiguobacterium sp., D55 was identified as Aeromonas sp., D30 was identified as Agrobacterium sp., D38 was identified as Arthrobacter sp., and D7 was identified as Pseudomonas sp..These six strains D11, D45, D51, D55, D52 and D53 were choosed to screen the potential probiotics which had high degradation ability. The results showed that these six strains could significantly degrade the organic matter in leach solution of tilapia feed, could significantly degradate the organic matter in supernatant of tilapia feed medium, and could decompose depositing particles of tilapia feed at the bottom.