乳酸菌发酵过程发酵液脂肪酸组生态位的异质性

为探究乳酸菌发酵过程中发酵液脂肪酸组生态位的异质性，测定8 种乳酸菌发酵过程中乳酸菌活菌数和发酵液脂肪酸组，分析生态位宽度和重叠度与乳酸菌生长的关系。结果表明，不同乳酸菌生长能力差异显著，鼠李糖乳杆菌FJAT-13807生长能力最强，嗜热链球菌FJAT-43774最弱。8 种乳酸菌发酵液脂肪酸组共检测到91 条生物标记，其中直链脂肪酸12 条、支链脂肪酸70 条、未能分离的脂肪酸9 条，其含量顺序为直链脂肪酸＞支链脂肪酸＞未能分离的脂肪酸。不同乳酸菌发酵液脂肪酸总量差异显著（P＜0.05），但乳酸菌发酵液脂肪酸总量与菌生长能力无直接相关性。发酵初期（1 h），不同乳酸菌发酵液的脂肪酸生态位宽度差异不显著，菌株间脂肪酸生态位重叠程度较高，活菌数较低，环境容量较大，生态位宽度与重叠无相关性；发酵中期（24 h），乳酸菌发酵液脂肪酸生态位宽度和重叠发生较大分化，影响处于对数生长期的乳酸菌生长模式，生态位宽度增加，乳酸菌生长速度下降，活菌数呈线性方程增长；生态位宽度减少，乳酸菌生长速度增加，活菌数呈抛物线方程增长；生态位宽度维持，乳酸菌生长速度维持原有方式；发酵后期（48 h），乳酸菌发酵液脂肪酸生态位宽度与重叠也有类似分化，此时，乳酸菌处于稳定消亡期，生态位宽度较宽，乳酸菌生长能力下降，活菌数呈指数方程下降；生态位宽度较窄，乳酸菌生长能力增强，活菌数呈一元三次方程变动；生态位宽度维持，乳酸菌维持原有的规律，活菌数呈幂指数下降。乳酸菌发酵液脂肪酸生态位宽度和重叠的变化可用于乳酸菌生长势和资源利用率评估，为乳酸菌生长生态学研究提供新思路。

Heterogeneity of Ecological Niche for Fatty Acid Lipidomics in Fermentation Broth during Fermentation Process of Lactic Acid Bacteria

The aim of this study was to explore the heterogeneity of ecological niche for fatty acid lipidomics in the fermentation broth of lactic acid bacteria (LAB) during the fermentation process. Eight LAB species were individually cultured in a mixed medium containing litchi juice and soybean protein. The number of viable bacteria and fatty acid lipidomics were detected during culture and the relationship of ecological niche width and overlap with bacterial growth capability was analyzed. The results showed that a significant difference in growth capability was found among LAB species. The growth capability of Lactobacillus rhamnosus FJAT-13807 was the strongest, while that of Streptococcus thermophilus FJAT-43774 was the weakest. A total of 91 biomarkers of fatty acid lipidomics were detected in the fermentation broths of the eight LAB strains, including 12 biomarkers of straight-chain fatty acids, 70 biomarkers of branched chain fatty acids and 9 biomarkers of complex fatty acids. The order of fatty acid contents was as follows: straight fatty acid > branched chain fatty acid > complex fatty acid. Total fatty acid contents significantly varied in the fermentation broths of different LAB species (P < 0.05), which showed no direct correlation with bacterial growth capability. At the initial stage of fermentation (1 h), there was no significant difference in the ecological niche width of fatty acid lipidomics in the fermentation broths of the eight LAB strains. The ecological niche overlap of fatty acid lipidomics between strains was high, the number of viable bacteria was low, the environmental capacity was large, and the niche width was not correlated with the niche overlap. In the middle of fermentation (24 h), the niche width and overlap of fatty acid lipidomics in the fermentation broth of LAB were significantly differentiated, which affected the growth mode of LAB in the logarithmic growth period. The niche width increased, the growth rate of LAB decreased promptly, and the number of viable bacteria increased in a linear manner. The niche width decreased, the growth rate of LAB increased, and the number of viable bacteria increased in a parabolic manner. The niche width was maintained, the growth rate of LAB was maintained at the original level, and the number of viable bacteria increased in an exponential manner. At the end of fermentation (48 h), the niche width and overlap of fatty acid lipidomics in the fermentation broth of LAB were similarly differentiated. At this time point, LAB were in the stable extinction period, the niche width was big, the growth capacity of LAB decreased, and the number of viable bacteria decreased exponentially. The niche width was small, the growth capability of LAB was enhanced, and the number of viable bacteria changed in a cubic manner. The niche width was maintained, the growth capability of LAB was maintained at the original level, and the number of viable bacteria decreased exponentially. The changes in niche width and overlap of fatty acid lipidomics in the fermentation broth of lactic acid bacteria can be used to evaluate the growth potential and resource utilization of lactic acid bacteria, which will provide a new idea for the ecological study of lactic acid bacteria growth.