Fast screening of bacterial suspension culture conditions on chips

Culture conditions including pH, nutrient concentration and temperature strongly influence the properties of a microbial strain by affecting many factors such as the microbial membrane and metabolism. We present a microfluidic chip for screening pH and nutrient content with a concentration gradient generator connected to eight parallel suspension culture loops and another chip for the screening of temperature with four different temperature zones under suspension culture loops. Bacteria grow much faster on chips than in test tubes, and yet interestingly, on-chip screening of culture conditions for E. coli yields results similar to those from a culture in test tubes, demonstrating the validity of the on-chip screening approach. The microfluidic chips were applied to study the growth conditions of two wild type Bacillus subtilis strains isolated from polluted water. The on-chip screening experiments show advantages of nanoliter scale screening units, high-throughput and requiring only one-fourth of the time.