Nuclear magnetic resonance studies of acetic acid inhibition of rec Zymomonas mobilis ZM4(pZB5)

The fermentation characteristics and effects of lignocellulosic toxic compo unds on recombinant Zymomonas mobilis ZM4(pZB5), which is capable of conver ting both glucose and xylose to ethanol, and its parental strain, ZM4, were characterized using C-13 and P-31 nuclear magnetic resonance (NMR) in vivo . From the P-31 NMR data, the levels of nucleoside triphosphates (NTP) of Z M(pZB5) using xylose were lower than those of glucose. This can be related to the intrinsically slower assimilation and/or metabolism of xylose compar ed to glucose and is evidence of a less energized state of ZM4(pZB5) cells during xylose fermentation. Acetic acid was shown to be strongly inhibitory to ZM4(pZB5) on xylose medium, with xylose utilization being completely in hibited at pH 5.0 or lower in the presence of 10.9 g/L of sodium acetate. F rom the P-31 NMR results, the addition of sodium acetate caused decreased N TP and sugar phosphates, together with acidification of the cytoplasm. Intr acellular deenergization and acidification appear to be the major mechanism s by which acetic acid exerts its toxic effects on this recombinant strain.