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The aim of this experiment was to study the biological characteristics and inhibitory mechanism of a novel Lactobacillus bacteriocin against Salmonella typhimurium. Whole genome sequencing was used to analyze the genomic information of bacteriocin-producing lactic acid bacteria, agar diffusion and dialysis methods were used to determine the bacteriocin inhibitory activity and molecular weight range, organic acid, hydrogen peroxide exclusion test and protease sensitivity test were used to determine the nature of bacteriocin, and the biological properties of bacteriocin were investigated by setting up pH value and temperature gradients, determining the growth curves and bacteriocin inhibitory curves of lactic acid bacteria, and the preliminary exploration of bacteriocin inhibitory mechanism was carried out by scanning electron microscope observation. Scanning electron microscope observation was used to explore the mechanism of bacteriocin inhibition. The results showed that a strain of Lactobacillus PG-9 with bacteriocin inhibitory activity was identified as Limosilactobacillus fermentum by molecular biology, with a full genome size of 1 985 177 bp, containing 1 947 coding genes. The bacteriocin PG-9B it produced had good bacteriostatic activity against Salmonella typhimurium, with an estimated molecular weight of less than 1 kDa. After excluding the effects of organic acids and hydrogen peroxide, it was found to be sensitive to various proteases, in the range of pH 3.0~7.0 and -20~121 °C, high antibacterial activity was retained. Scanning electron microscopy showed that the Limosilactobacillus fermentum citriodora bacteriocin PG-9B inhibits and kills cells by disrupting the cell surface morphology of Salmonella typhimurium. The study indicates that the favorable biological properties of Limosilactobacillus fermentum bacteriocin PG-9B can be used as a potential alternative antioxidant additive for the control of Salmonella typhimurium in the feed industry. [ABSTRACT FROM AUTHOR]

Based on the investigation data of phytoplankton in Dianshan Lake from May to October in 2009, the characteristics of phytoplankton community and the dominant species succession are studied. The results show that Cyanophyta and Chlorophta are the main taxa. Cyanophyta is dominant in cell abundance and Chlorophta is dominant in species variety. From the flat distribution, the species variety and density of Cyanophyta are higher in west and southwest. The peak of cell density reaches 23.40 x 10(7) cells x L(-1) in September due to the occurrence of cyanobacterial bloom, Cyanophyta account for 90.3 percents, with significant differences in each point (ANOVA, P < 0.05). An obvious succession of phytoplankton species is found, Microcystis of Cyanophyta become the dominant taxa and then conglutinated together to form water bloom. Temperature and pH are the main factors that affect the cyanobacterial bloom, and wind direction is an important reason for the horizontal distribution of the bloom-forming Microcystis. The phytoplankton diversity index is poor in central and western sites, diversity index decreases during cyanobacterial bloom and the community structures are simple.