Experiments
Preliminary experiments were conducted to optimize and validate the complete bioreactor setup and its individual components. The configurations of the aeration pump (the 3D spring structure) was enhanced to pump air at a rate of 10 mL/min, to achieve an aeration rate of 1 vvm in the reactor.
Preliminery Runs
Before the development of our continuous OD device, an initial experiment was carried out in the mini-bioreactor and growth was manually monitored using the laboratory spectrophotometer. We used E. coli DH5alpha strain in LB medium and the experiment was run for 110 hours.
Final Experiment
The experiment for characterization of the chemostat Bioreactor consisted of a Batch mode followed by the Continuous mode with 3 different dilution rates. We used #RP1O# strain in minimal Carbon medium M9.
The experiment was designed to keep the dilution rates constant for 3 reactor volumes, so as to obtain constant Optical Density, an indication of the Biomass, within human sampling error, to achieve proof of concept.
The Batch mode ran for 5 hours until we observed OD above the threshold of 1.0 in the reactor.
The continuous mode of operation was initiated with a dilution rate of 0.1 h-1 at hour 5. Constant OD was obtained for 9 hours. However, the feed pump was observed to be pumping more medium than the harvest removed by the harvest pump. Hence at our 30, the Master Control Program was modified to change the speed of the harvest pump accordingly. The harvest pump rate was changed to pump 30% faster than the feed pump. The change made is reflected in reduction of OD from an average value of 0.78 to 0.76. At hour 48, the first step change in dilution rate was made to 0.3 h-1. The OD was observed to be stable with few variations within pipetting error. A final step increase in dilution rate was carried out at hour 63, where the dilution rate was increased to 0.4 0.3 h-1. This resulted in OD values for 3 reactor volumes, which lasted for 7.5 hours.
The continuous mode was started with dilution rate of 0.1-1 at hour 5. Constant OD was obtained for 9 hours but soon it was observed that the feed pump was supplying more medium than the harvest removed by the harvest pump. At hour 30, we decided to modify the Master Control Program to change the speed of the harvest pump. Therefore, the harvest pump rate was changed to pump 30% faster than the feed pump. This can be observed in the reduction in the OD from an average of 0.78 to 0.76.
At hour 48, the dilution rate was changed, for step 2 of the experiment, to 0.3-1. The OD was observed to be stable with few variations within pipetting error.
The step 3 was carried out at hour 63, with dilution rate at 0.4-1. This resulted in OD values for 3 reactor volumes, which lasted for 7.5 hours.