P49: Intrinsic growth and substrate utilization kinetics parameters for Oscillibacter sp., a CO-utilizing acetogenic bacterium

Despite the fact that Carbon monoxide (CO) is toxic to humans and other species, it is used as sole carbon and energy source by anaerobic microorganisms called as “acetogens”, and produce energy dense fuels and useful chemicals. Thus the biological conversion of CO and H₂ rich synthesis gas (syngas) has been an area of interest for the researchers in the recent decades. However, the low solubility of CO and its high affinity to metal ions in the CO oxidizing enzymes are the big hurdles to achieve a successful operation of commercial sized bioreactor. Hence it is desired to find the optimum concentration of the CO that do not inhibit the microbial growth and efficiency of CO oxidizing enzymes in the fermentation media.

The aim of this study was to evaluate the CO utilizing capacity for a newly isolated strain which is identified as Oscillibacter sp. cow-5. This strain produces various chemicals: acetate, butyrate and small amount of ethanol and iso-valerate from CO under strict anaerobic conditions. The strain was grown in batch reactor under optimum growth conditions and a modified Monod equation was used to determine the maximum growth rate (µ_max) and Monod constant (K_s). Simulated data were well fitted with experimental one, and two parameters, µ_max and K_s, were estimated as 0.13h^-1 and 0.086 mM CO, respectively using a nonlinear second order regression. Meantime, the apparent dissolved CO inhibition has been found at 0.8 mM CO (≈1 atm of P_CO) from the plot of C* vs.  C*/µ.