The effect of CO2 ventilation on kinetics and yields of cell-mass and ethanol in batch cultures ofZymomonas mobilis

Abstract

The effect of CO2 removal by continuous sparging of N2 in batch cultures ofZymomonas mobilis (ATCC10988) was examined. N2 sparging considerably reduces lag times in batch cultures, possibly because of continuous removal of CO2 from the culture media. Ventilation of CO2 from culture media results in an increase of about 15% in the average specific growth rate and about 12% in the cell-mass yield with no noticeable trend in the average specific glucose uptake and ethanol production rates. The overall ethanol yield on glucose, however, decreases slightly by 5%. Analysis of ventilated experiments show that the CO2 production is directly coupled with the ethanol formation but not necessarily with the cell-mass production, indicating a decoupling of growth from ethanol production. Further, comparison of ventilated and non-ventilated experiments rules out the possibility of CO2 accumulation in the culture media as a factor responsible for increasing growth inhibition and decoupling of growth from ethanol fermentation at increasing initial glucose concentrations in batch cultures.