Stress-induced physiological responses to starvation periods as well as glucose and lactose pulses in Bacillus licheniformis CCMI 1034 continuous aerobic fermentation processes as measured by multi-parameter flow cytometry

Multi-parameter flow cytometry (MPFC) coupled with specific fluorescent stains were used to monitor the physiological response of individual cells to starvation periods as well as lactose and glucose pulses during the steady state of a continuous culture of Bacillus licheniformis. Measurements of off-gas (CO2 produced and O2 consumed) and optical density measurements were also made and used to follow bulk biomass proliferation and metabolic activity of the microbial population. It was clear that the physiological response to each perturbation was different in type and extent dependent on the conditions experienced and that these responses could be followed by the techniques employed. The use of MPFC, a rapid, real time analysis of individual microbial cells, is enhancing our knowledge of how different physiological sub-populations develop with time (population dynamics) throughout a bio-process further demonstrating the inherent complex heterogeneity of microbial cultures even during the so called 'steady-state' of a continuous culture fermentation. These results are discussed in terms of devising better control systems based on measurements made at the individual cell level for optimisation of bioprocess performance.