Cell yield and growth of Bifidobacterium longum subsp. infantis B8762 at different incubation temperature conditions

Bifidobacteria exhibits limited growth despite adequate nutritional conditions. To elucidate this phenomenon, a detailed analysis of its division cycle was conducted. Bifidobacterium longum subsp. infantis B8762 was used as a model organism. Cells were labeled with fluorescent probes, and flow cytometry was employed to analyze division progression, membrane integrity, and the expression levels of cell division–related genes were analyzed by absolute quantification using the qPCR method at different temperatures. The results demonstrated robust growth at a fluorescent dye concentration of 10 μmol/L, which was suitable for observing the division process. The distribution of cell populations across generations varied under different culture conditions, suggesting an ongoing but asynchronous division. Notably, the population size of the 6th generation at elevated temperatures showed a 142.31% increase compared with that at 37°C. Culture temperature profoundly affected the physiological state of the strain, with higher temperatures causing a 168.82% increase in the proportion of cells with compromised membrane integrity. Concurrently, the expression of key division genes ( ftsZ and ftsK ) was downregulated by 38.26% and 43.30%, respectively, at 42°C compared with 37°C. This study revealed fluorescent signaling characteristics, differences in cellular viability, and gene regulatory responses during the proliferative division of bifidobacteria. These findings provide theoretical guidance for the industrial production and fermentation stability of highly active lactic strains. • A concentration of 10 μmol/L CFDA-SE was identified as optimal for tracking bacterial division without significant physiological interference. • Elevated culture temperature accelerates cell division rates but concurrently compromises membrane integrity and cell viability. • Expression of essential division genes fts Z and fts K is significantly suppressed under 42°C thermal stress. • Cell size distribution shifts toward larger dimensions when division is inhibited at higher temperatures.