Journal of Biotechnology & Biomaterials
Open Access

Abstract

Accumulation of certain metabolic products during fermentation is known to adversely affect cellular physiology and hence, reduce the microbial productivity. Ethanol is one such product. Product inhibition due to ethanol can be reduced by removing it from the fermentation broth as it is being produced. This strategy was investigated for ethanol production from the anaerobic bacterium Zymomonas anaerobia. Z. anaerobia has the advantage of not requiring aeration during ethanol production and it can thrive in highly concentrated solutions of glucose. This reduces the broth handling requirements, the capital costs for a given production rate and the cost of recovery of ethanol. In Z. anaerobia, ethanol inhibited its own production at a concentration of greater than 20 g/L. Temperature at 35 �ºC appeared to be an optimal in the Z.anaerobia fermentation. With this temperature, the specific growth rate and ethanol productivity of 0.304�±0.011 h-1 and 4.333�±0.099 g.Lâ��1.hâ��1 were obtained, respectively. Ethanol productivity could be enhanced by in situ extractive fermentation in which water-immiscible organic solvents were used to remove the ethanol from the fermentation broth as it was being produced. Several solvents including vegetable oils were experimentally evaluated for biocompatibility with Z.anaerobia and the ability to extract ethanol during batch fermentation. Solvents that were found to be nontoxic to Z. anaerobia were used for in situ batch extractive fermentations in a 2 L stirred bioreactor (1:1 ratio of solvent and fermentation broth) with an optimal glucose concentration of 150 g.Lâ��1, 35 �ºC and an agitation speed of 100 rpm. Oleyl alcohol, iso-octadecanol and 2-octyl-1-dodecanol were the three solvents that were found to be nontoxic to Z. anaerobia. With these solvents, the cell viability relative to control (no solvent) was 1.48�±0.4, 1.03�±0.18 and 1.05�±0.07, respectively after two days of exposure. Besides, all solvents tested improved biomass concentration, glucose consumption and ethanol concentration relative to control, but iso-octadecanol was clearly the most effective solvent. Using iso-octadecanol the maximum ethanol concentration of 75�±3.07 g.Lâ��1 was nearly 1.25-fold that of the control fermentation. For this solvent, the ethanol yield on glucose was 0.485�±0.005 g.Lâ��1 compared to a yield of 0.468�±0.005 for the control culture. Productivity enhancement of Z. anaerobia ethanol fermentation will be discussed.

Biography

Email: azilahajit@ump.edu.my