Study On The LacticAcid Bacteria Biodiversity Isolated From The Intestinal Tract Of Cold-Water Fish And The Screening Of Bacteriocin Producing Strains

Object: Bacteriocins secreted by lactic acid bacteria are antibacterial peptides or proteins, which candegraded by proteases in the gastrointestinal tract and have high security, effectively against the growth offoodborne pathogenic and spoilage bacteria. Bacteriocins have great potential application for their possibleuse as a natural biopreservatives in the food industry. The objects of this study were to to isolate andidentify lactic acid bacteria (LAB) from intestinal tracts of wild cold water fish which were collected fromnorthern area of Xinjiang, China and Heilongjiang valley, and analysis the diversity of isolated LAB; thescreening of characterization of bacteriocins produced by LAB from cold water fish intestinal tracts werealso performed.Methods: The isolation and diversity analisis of LAB from intestinal content and mucosa samples of coldwater fish were carried out by culture-independent methods using MRS, Ellliker, M17agar, Bile EsculinAzide Agar and Lactobacillus Selective Agar. Bacteriocin-producing LAB strains were screened andcharacterizated by agar well diffusion method. Bacteriocin stability was studied in different temperature, pH,surfactants and enzymes.Results:195pure cultures were isolated from21different wild cols water fish intestinal samples, and149LAB strains identified initially based on their16S rDNA sequences, belong to genera of Carrobacterium(73), Lactobacillus (70), Bacillus (1) and Leuconostoc (5) respectively.20LAB strains showedantimicrobial activity after eliminating organic acid and hydrogen peroxide by screening the antibacterialactivity of149strains. The activity of all tested strains was lost after treatment with proteinases and theinhibitory compound was proteinaceous in nature. Three strains named M17-ZLYM-4, M17-ZLYM-3andBS-ZLYM-4showing obvious inhibitory activities against Listeria monocytogenes were selected for furthercharacterization. The results suggested that the inhibitory substances from the three strains were stable toheat (24°C~100°C) and little influence on surfactants, active over a quite wide pH range (2~9), and theantimicrobial activity was lost after treatment with proteinase K, trypsin and pepsin. The optimum growthtemperature of strains is controlled on24°C, belongs to produce bacteriocin resistance of lactic acidbacteria at low temperature.Conclusions: The biodiversity of cultured LAB isolated wild cold water fish intestinal tracts is relativelyrich, and the genus Carrobacterium and Lactobacillus occupy the superiority in numbers. The screening andpreliminary identification of antimicrobial activity show20strains are bacteriocin-producing LAB.Bacterion-producings strains M17-ZLYM-4, M17-ZLYM-3and BS-ZLYM-4were stable to heat, active overa quite wide pH range (2~9) and sensitive to protease; the optimum growth temperature is controlled in24°C,belong to the category of bacteria resistant to cold, and can be used as a potential biopreservative in foodpreservative field.