Team:Aalto-Helsinki/LabResults
Laboratory Results
Continuous production
The chemostat cultivation of E.Coli BL21(DE3) was successful. Batch phase took six hours, and soon after starting the process dissolved oxygen amount decreased into zero. Therefore, oxygen became the limiting factor of growth. Continuous process was started and the first steady state was reached 39 h after starting to feed fresh media into the reactor. With 1,0 l/h aeration, the density of cell population was calculated to be 9,85 g/L at this point, which can be assumed relatively high. Interestingly, bacteria acted as facultative anaerobe when changing its oxygen uptake depending on the growth phase. IPTG induction started with 2mM concentration and the population growth reacted right away to changed process conditions. New steady state was achieved 40 h later and the population density became 9,28 g/L. Thus, there was a 0,57 g/L difference of the biomass between the normal growth and the growth with propane production.
Reactor's glucose consentration decreased from original 20 g/l to zero during the exponential grow phase as the cells used it as a carbon source. However, it was hard to recognize which was the limiting factor of growth and production, glucose or oxygen? During the first steady state, glucose concentration increased when the need for the catabolism of biomass was lower. The end of batch phase, before started feed freash media, was determined from decreased pH-level when the cells produced acids as a response for nutrient deficiency. TB-media used for cultivation contained phosphates which had buffer capacity but it wasn't enough. pH-control was assembled in order to maintain pH-values above 5,0.
Bacillus