NOVELTY - New recombinant bacterial host cell (C1) comprises: xylose metabolic pathway comprising at least one gene encoding polypeptide having xylose isomerase activity; at least one gene encoding polypeptide having ribose-5-phosphate isomerase activity; and at least one genetic modification that increases ribose-5-phosphate isomerase activity in host cell compared with ribose-5-phosphate isomerase activity in host cell lacking genetic modification; where host cell utilizes xylose to produce ethanol, and bacterial host cell is selected from Zymomonas and Zymobacter.    USE - As recombinant bacterial host cell useful for producing ethanol from xylose (claimed), where ethanol is useful as fuel for replacing fossil fuels.    ADVANTAGE - The recombinant bacterial strains of Zymomonas and Zymobacter provide imprived strains exhibiting improvement in xylose utilization to produce ethanol. The bacterial strains are engineered to have increased ribose-5-phosphate isomerase (RPI) activity. It is discovered that in strains where xylose isomerase activity is high, carbon flux to RPI is also high and results in generation of undesirable by products ribulose-5-phosphate and/or ribulose (catalyzed by cellular phosphotases), which accumulate in medium. Generation of these by-products siphons off carbon that could be used in production of ethanol. Increasing activity of RPI directs more carbon to desired products of xylose metabolic pathway (fructose-6 phosphate and glyceraldyhyde-6 phosphate) which are used in generation of ethanol. Thus, in xylose-utilizing Zymomonas or Zymobacter strains that accumulate ribulose-5-phosphate and/or ribulose when grown in xylose containing medium, increase in RPI activity improves cell growth, xylose utilization, and ethanol production. When ribulose is produced as side product in xylose utilization, increased RPI activity provides improved xylose utilization, which is desired for growth in media containing xylose including saccharified biomass, leading to increased ethanol production. Ethanol is an important compound for use in replacing fossil fuels and saccharified biomass provides renewable carbon source for ethanol production by fermentation, while involving optimal utilization of xylose by the microorganism. Thus the engineered strains result in increased efficiency in xylose utilization, and thus to higher ethanol yields when fermentation is in xylose containing media. Ribulose can be produced by conversion of ribulose-5-phosphate to ribulose by phosphatase. If ribulose-5-phosphate accumulates in cell it can provide substrate for cellular phosphatases. The conversion of ribulose-5-phosphate to ribulose and accumulation of ribulose in medium indicates enzymatic deficiency in pathway responsible for metabolizing xylose to ethanol. Conditions under which initial step in metabolism of xylose, catalyzed by xylose isomerase, has been increased can act to intensify this deficiency leading to even higher levels of ribulose-5-phosphate and ribulose accumulation. The presence of increased RPI activity in cells, along with further increased xylose isomerase expression, leads to further increased ethanol Production e.g. ethanol production can be increased by at least 10, 15, 20, or 25%. Reducing production of ribulose and improving ribulose-5-phsphate utilization in xylose metabolism and ethanol production pathways improve production of ethanol from xylose.    DETAILED DESCRIPTION - An INDEPENDENT CLAIM is included for process (P1) for producing ethanol involving:    (A) providing the recombinant bacterial host cell (C1); and    (B) culturing the bacterial host cell of step (A) in a medium comprising xylose so that xylose is converted to ethanol.    DESCRIPTION OF DRAWING(S) - The figure shows diagram of xylose metabolism and ethanol fermentation pathways in Zymomonas engineered for xylose utilization.