介质阻挡放电等离子体对不同pH值生长的酸土脂环酸芽孢杆菌的灭活作用

该研究探讨了介质阻挡放电等离子体对不同pH值（3.2、3.6、4.0和4.4）下生长的酸土脂环酸芽孢杆菌的杀灭作用。研究发现等离子体对最适生长pH值4.0下的酸土脂环酸芽孢杆菌杀灭效率最低，pH值升高（4.4）或降低（3.2、3.6）均引起致死率增加（P<0.05）。例如30 kV处理2 min条件下，等离子体对pH值为4.0生长的酸土脂环酸芽孢杆菌致死率为4.8个对数，对pH值为3.2、3.6和4.4生长的菌体致死率分别为5.9、5.4和5.1个对数。等离子体对不同pH值培养的酸土脂环酸芽孢杆菌致死率的差异可能与菌体形态和膜脂质成分有关。扫描电镜观察发现，pH值3.2和3.6培养的菌体出现异常伸长形态，且酸土脂环酸芽孢杆菌在pH值3.2条件下更为明显，更易被等离子损伤而导致死亡。气相-质谱联用结果表明相比于最适pH值4.0，pH值4.4生长条件下环己烷十一酸相对含量显著提高（67.86%），而环戊烷十三酸降低（22.21%）（P<0.05），使得等离子体产生的氧自由基等成分在细胞膜中的堆积，而导致菌体更易被杀灭。该研究表明菌体耐受性增加与酸土脂环酸芽孢杆菌细胞膜脂肪酸成分和形态变化存在一定的相关性。

Inactivation of Alicyclobacillus acidoterrestris Grown at Different pH Values using Dielectric Barrier Discharge-atmospheric Cold Plasma

The effects of dielectric barrier discharge-atmospheric cold plasma (DBD-ACP) on the inactivation of Alicyclobacillus acidoterrestris grown at different pH values (3.2, 3.6, 4.0, and 4.4) were investigated. The inactivation efficiency against A. acidoterrestris grown optimally at pH 4.0 was the lowest. An increase in pH (4.4) and a decrease in pH (3.2, 3.6) both lead to increased lethality (P<0.05). The inactivation on A. acidoterrestris grown at pH 4.0 using DBD-ACP was 4.8 log under 30 kV treatment for 2 min and was 5.9, 5.4, and 5.1 log for A. acidoterrestris grown at pH 3.2, 3.6, and 4.4, respectively. The difference in the inactivation of A. acidoterrestris cells cultured at different pH using DBD-ACP could be attributed to the changes in morphology and membrane fatty acid composition of A. acidoterrestris cells. Scanning electron microscopy (SEM) observations indicated that the bacteria cultured at pH 3.2 and 3.6 displayed abnormal elongation, which was more obvious at pH 3.2, indicating an increased susceptibility to DBD-ACP. The gas chromatography-mass spectrometry (GC-MS) results indicated that the relative content of cyclohexaneundecanoic acid (67.86%) was significantly increased at pH 4.4, compared to that at optimum pH 4.0, whereas the cyclopentanetridecanoic acid content (22.21%) decreased (P<0.05), facilitating the accumulation of oxygen free radicals and other components generated by DBD-ACP in the cell membranes, and causing bacterial death. The higher tolerance of A. acidoterrestris to DBD-ACP is related to the changes in its fatty acid composition and morphology of the cell membrane.