Composition Characteristics And Application Effect Of Enterococcus Faecalis HN000F7 Preparation In Secondary Open Expansion

With the increasing intensification and commercialization of aquaculture production,many problems inevitably emerged.Problems such as the deterioration of aquaculture water environment,the abuse of antibiotics and frequent disease have been seriously hindering the development of the industry.Although the use of probiotics solved these problems,the use of it in bulk can lead to increased farming costs.In recent years,on the basis of practices,many farmers expand the cultivation of commercial probiotics through a simple open process.The product was used to high density culture of prawn and had excellent effect on improving water quality and animal health.However,the dynamic changes of microorganisms and their metabolites during culture have not been revealed.In this study,high-throughput sequencing and HPLC-MS/MS were used to study the composition and dynamic changes of microorganisms and substances in the secondary open expansion process of probiotics,and then the application effect was evaluated by litopenaeus vannamei culture experiment.The main conclusions are as follows:(1)The open process could not realize the expanded culture of Enterococcus faecalis HN000F7.Inoculation of probiotics changed the early expansion environment,affected the bacterial community structure in the cultivate system,and caused the evolution of bacteria in different directions.Enterococcus,Bacillus and Vibro were the dominant microbial groups in the expanded culture products.Bacillus was the absolute dominant bacterium in the expansion products,and its relative abundance increased during the expansion process,which might be the reason for the excellent effect of the expansion products on improving water quality.(2)The metabolites of the secondary expansion products of probiotics are mainly composed of amino acids,peptides,fatty acids,carbohydrates,aldehydes and ketones,aliphalosides and so on.The material changes dramatically during the expansion process.The product contains a large number of amino acids,carbohydrates,fatty acids and other metabolites.This is the material basis for the excellent application effect of probiotics.(3)The secondary expansion products of probiotics can effectively remove ammonia nitrogen and partially remove nitrate and nitrite in the culture system.The results of highthroughput sequencing showed that the relative abundance of Rhodobacterales in the culture system could be increased by using the secondary expansion products of probiotics.In this study,the composition rules of microorganisms and metabolites in the secondary expansion products of probiotics preparations were clarified,which provides a scientific basis for the rational use of secondary expansion products of probiotics and helps to build an efficient and healthy culture model for Litopenaeus vannamei.