| Geosmin(GSM)is one of the main components of earthy odors in fresh water.At the same time,it is also one of the causes of earthy odors in fish muscle.Odontoxins are terpenoids produced and secreted by microorganisms.In eutrophic aquaculture ponds,odontoxins often cause serious odour problems,which pose a threat to aquatic organisms and human beings in water.For freshwater aquaculture products,odontoxins not only affect the use value of products,but also reduce the commercial value,and the use safety is also questioned.At present,the research on soil odor is mainly concentrated in drinking water,and there is less research on the removal of soil odor in aquaculture.Therefore,it is of great significance to study the removal technology of soil odor in aquaculture.The purpose of this study is to explore the source of GSM in water and muscle of tilapia,the way of GSM intake from intestine,and to find a kind of bacteria which can efficiently degrade Geosmin in aquaculture.The results are as follows:1.GSM was detected in both water and tilapia meat of tilapia culture system.The content of GSM in water ranged from 17.79 ng/L to 42.47 ng/L,and that in Tilapia muscle ranged from 409.77 ng/kg to 1062.72 ng/kg The results showed that the body weight of tilapia was heavy,the size of tilapia was large,the body fat content was high,and the content of GSM in muscle was also high.Compared with other groups,the content of GSM in muscle of tilapia was higher at 1% and 8% feed rates.2.Different feed rates interfere with the community structure of phytoplankton in the cultured tilapia by inputting different amounts of nutrients into the tilapia culture system,and then affect the content of GSM in the water;the main algae species that affect the content of GSM in Tilapia meat and water are not consistent,which needs further study.The GSM in Tilapia meat is mainly fed by tilapia itself It is digested and absorbed by intestine and enriched in fish.Therefore,it is very important to change the feeding mode of bait and feed reasonably for controlling the production of earthy odor.3.The average content of GSM in Tilapia muscle cultured in pond was 588.89 ng/kg,and that in Tilapia muscle cultured in barrel was 642.92 ng/kg The results showed that the average GSM content of tilapia muscle in the cage was higher than that in the pond,and there were differences among different species;through high-throughput sequencing,the GSM synthase genes in the intestine were mainly from filamentous algae and Microcystis aeruginosa,and the linear regression analysis showed that the GSM synthase genes of Filamentous algae and Microcystis aeruginosa had no correlation with the GSM content in the muscle This may involve the difference of gene expression.4.The copy number of cyanobacteria derived GSM synthase gene in intestine varied greatly among different individuals by fluorescence quantitative determination.Linear regression analysis showed that there was a correlation between cyanobacteria derived GSM synthase gene in intestine and the content of GSM in Tilapia muscle.It was likely that the content of GSM in Tilapia muscle was related to the algae with less content of GSM synthase gene in intestine through intestinal intake.But at the same time,it can not be ruled out that actinomycetes and other fungi which can produce GSM,cyanobacteria and Streptomyces which can produce GSM in Tilapia muscle through the way of intestinal intake,whose contribution value is greater,need to do further research and analysis.5.Three GSM degrading bacteria Geo-1,Geo-2 and Geo-3 were isolated from the sediment of tilapia pond,and their morphological characteristics were pink,white and yellow,respectively.By 16 Sr DNA phylogenetic tree analysis,the three bacteria were methylbacillus,bacillus and neosphingosine bacteria,respectively.The degradation ability evaluation results showed that they were different from the previous reports The degradation rates of GSM by the three degrading bacteria were 96.14%,93.32% and 93.79% respectively,and the degradation rate of high concentration GSM(100 μg/L)could reach 97% during the degradation period.The optimal degradation conditions of GSM by the three degrading bacteria need to be further studied. |
