Microfluidic cultivation enables probiotic growth under thermal stress
Thermal stress tolerance is essential for preserving the viability and functionality of probiotic bacteria. Conventional batch cultures offer limited control over temperature changes across space and time. We have introduced an integrated microfluidic platform to continuously cultivate bacteria within a precisely defined and tunable thermal environment, and used Lacticaseibacillus rhamnosus as a model system. The device features serially connected microchambers with independently controlled heating zones, creating distinct and dynamic thermal profiles as the bacteria travel from one microchamber to the next. Biomass accumulation was observed at 37 {degrees}C within 48 h in all microchambers, no growth occurred at 49 {degrees}C even after 72 h. When the cells were exposed to a periodic thermal landscape, where an increase in temperature in one chamber was followed by a return to 37 {degrees}C in the next, growth was observed in the last chamber (49 {degrees}C) after three days indicating adaptation to thermal stress. Cells that grew on-chip at 49 {degrees}C showed no growth in off-chip experiments. Continuous monitoring of pH at the chip outlet confirmed ongoing metabolic activity in growing populations. Tailored microfluidic thermal environments were shown to help bacteria grow even under otherwise inhibitory conditions.