Abstract: 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.

Key words: lactic acid bacteria; fermentation process; fatty acid lipidomics; niche width; niche overlap