1-48: CO2 auxostat as a tool for developing fast-growing CBP organisms

Consolidated bioprocessing (CBP) has gained interest as a potential method of industrial biofuel production.  In order for CBP to become industrially feasible, considerable effort is going into developing organisms capable of combining cellulose solubilization and fermentation.  Another important aspect in CBP development is the need for organisms capable of performing these steps in industrially relevant time scales.  To this end, we have developed a CO₂ auxostat as a tool for applying selective pressure for fast-growing CBP organisms.  The auxostat control algorithm was developed in LabVIEW and is coupled with the inlet media pump and an offgas system capable of measuring CO₂.  When CO₂ levels extend beyond the target range, the feed rate of the inlet media pump is adjusted to maintain a constant CO₂ level.  Changes in the feed rate are recorded by measuring the mass of the waste carboy.  Using Clostridium thermocellum as a model organism, we have demonstrated the ability to select for a strain capable of growing at a significantly higher dilution rate.  Subsequent batch fermentations of selected and control strains revealed that the selected strain had growth and CO₂ production rates that were nearly twice as fast as the control strain.  Further analysis was also performed on these strains to characterize differences in substrate utilization and product formation.