Quorum Sensing Research Of Dominant Microflora Of Apostichopus Japonica Suffers From The Skin Ulceration Syndrom

Sea cucumber (Apostichopus japonicus) is well known for its nutrient-rich with abundant collagen and proteoglycans. Its role in medical care is more and more important and the application of it is more and more widely. The market of trade and consumption of sea cucumber was formed and enlarged with China as its center. The requirement of sea cucumber was mushroomed, and consequently, sea cucumber farming emerged as the times require. However, with the rapid development, various diseases appeared, and it caused serious economic losses. The skin ulceration syndrom has been payed much attention because of its infectivity and serious influence.At present, the prophylactic and sanative measures are mainly dependent on chemicals, but the misuse of it badly polluted the environment and limited the development of sea cucumber farming. Quorum-sensing as a cell-density-dependent signaling mechanism in many microorganisms, regulates many specialized processes such as sporulation, genetic competence, bioluminescence, and especially virulence. Therefore, studying on quorum-sensing and searching for an approach to biologically control bacterial diseases in animal by manipulating bacterial autoinducers became research focus.In gram-negative bacteria signal molecules are usually acylated homoserine lactones (AHLs) which differ in the structure of their N-acyl side chains. The AHLs detection can be based on different bacterial bioassays as well as physical technology such as HPLC, mass spectrometry and NMR spectroscopy. Thin-layer chromatography combination with biosensor also can used to screen AHLs. Bacterial bioassay is so simple, rapid and sensitive that it is used widely.In order to investigating the relationship between the skin ulceration syndrom of sea cucumber Apostichopus japonica and quorum sensing of bacteria, pathogenic bacteria C6 was used to infect the healthy sea cucumber and autoinducers in seawater of different infection period were detected with Strain Agrobacterium tumefaciens KYC55, and the detection method was optimized. The results show that the density of different kinds of seawater is different. The density of AHLs in seawater of sick period is higher than that from the initial stage of re-infection.The pathogenic bacteria C6 and bacterial isolates which were isolated from suffered sea cucumber were inspected also by Strain KYC55 to detect the secretion of AHLs. The results show that the bacterial isolates 4, C6, TB, BP3 and BP4 can secret AHLs, but the concentration of AHLs in the culture solution of different growth phase is various. The maximum concentration is appearance in the telephase of logarithmic growth phase.AHLs from different bacterial isolates were extracted from the culture solution, and thay were detected by strain KYC55 as well as Chromobacterler violaceum CV026. The effect of extraction methods was investigated. The optimum extractant is ethyl acetate (acidified by supplementing with 0.5% formic acid). Among 7 infecting microbial communities of suffered sea cucumber screened by Strain KYC55, bacterial isolates 4, TB, BP2, BP3, BP4 and C6 were found positive strains which can secret AHLs. But the activity of AHLs is all different from each other, from the highest to the lowest are 4>TB>BP4>BP3>C6, and the quality is different too. Bacterial isolate BP6 was negative strains which can not secret AHLs.Bacterial isolates 4, TB, BP2, BP3, BP4, BP6 and the pathogenic bacteria C6 all show high similarity with pathogenic bacterial isolates in aquiculture, and six of them can use AHLs as their signal molecular. The study was found that the quorum sensing of bacteria was one reason that cause disease of sea cucumber.