Tuesday, May 1, 2012
Napoleon Ballroom C-D, 3rd fl (Sheraton New Orleans)
The aim of this work was to study the performance of the ethanologenic E. coli strain MS04 (MG1655 ΔpflB, ΔadhE, ΔfrdA, ΔldhA, PpflB::pdcZm-adhAZm) using free cells (FC; static cultures) and immobilized cells on alginate (ICA; agitated cultures, 110 rpm). Batch non-aerated cultures were carried out with glucose (40 g/L) as the carbon source, and 3.7 g/L of FC or the equivalent amount of ICA. The effect of pH (7.0 and 5.5) in phosphate buffers was tested at 37ºC. The recycle of the biocatalyst was studied to evaluate the potential use of ICA for simultaneous saccharification of cellulose and glucose fermentation to ethanol (SSF) (pH 5.5, acetate buffer). Change of pH from 7.0 to 5.5 reduces the specific rates of glucose consumption (qGLC) and ethanol production (qEtOH) by 44% and 49%, respectively, for FC; moreover ethanol yield (YEtOH) was above 93% of the maximum theoretical at both pH values. For ICA, the reduction of pH from 7.0 to 5.5 decreases the qGLC only 21%; but the YEtOH were only 33% to 50% of the values found for FC. Furthermore, qEtOH was reduced 77% for ICA, and therefore the ethanol titers, each time the biocatalyst was recycled. These results show that immobilization of ethanologenic E. coli cells on alginate beads is not suitable for SSF because ethanologenic cell stability is not improved and productivity and yield of ethanol are reduced in comparison with free cells.