TECHNOLOGY FOCUS - BIOTECHNOLOGY - Preferred Microorganism: At least one genetic modification that increases ribose-5-phosphate isomerase activity is over-expression of an endogenous gene encoding a polypeptide having ribose-5-phosphate isomerase activity; and/or expression of at least one non-endogenous gene encoding a polypeptide having ribose-5-phosphate isomerase activity. The gene encoding a polypeptide having xylose isomerase activity is over-expressed, or is expressed in multicopy. The recombinant microbial host cell further comprises at least one genetic modification which increases xylose isomerase activity as compared to xylose isomerase activity in the microorganism lacking the genetic modification. Preferred Polypeptide: The polypeptide having ribose-5-phosphate isomerase activity has the EC classification of EC 5.3.1.6 (preferably ribose-5-phosphate isomerase A, or ribose-5-phosphate isomerase B). The ribose-5-phosphate isomerase A polypeptide gives an E-value score of less than or equal to 0.1 when queried using a Profile Hidden Markov Model (HMM) prepared using (SEQ ID NOs: 83 to 97) as available on WIPO website; where the query is carried out using the hmmsearch algorithm where the Z parameter is set to 1 billion; and has aspartic acid and glutamic acid at positions corresponding to 107 and 129, respectively, in the Saccharomyces cerevisiae ribose-5-phosphate isomerase A (RPI-A) protein of (SEQ ID NO: 97). The ribose-5-phosphate isomerase A has an amino acid sequence having at least 90% identity to an amino acid sequence selected from (SEQ ID NOs: 83 to 1212) as available on WIPO website, based on the Clustal W method of alignment using the default parameters of GAP PENALTY = 10, GAP LENGTH PENALTY = 0.1, and Gonnet 250 series of protein weight matrix (preferably the ribose-5-phosphate isomerase A has an amino acid sequence having at least 90% identity to an amino acid sequence selected from (SEQ ID NOs: 83 to 97) based on the Clustal W method of alignment using the default parameters). The ribose-5-phosphate isomerase B polypeptide gives an E-value score of less than or equal to 0.1 when queried using a Profile Hidden Markov Model prepared using (SEQ ID NOs: 1213 to 1217) as available on WIPO website; where the query is carried out using the hmmsearch algorithm where the Z parameter is set to 1 billion; and either has cysteine and threonine at positions corresponding to 66 and 68, respectively, in the E. coli RPI-B protein of (SEQ ID NO: 1216) or has serine and glutamic acid at positions corresponding to 68 and 72, respectively, in the Mycobacterium tuberculosis RPI-B protein of (SEQ ID NO: 1213); and has asparagine, glycine, aspartic acid, serine, or glutamic acid but not leucine at the position corresponding to 100 in the E. coli RPI-B protein of (SEQ ID NO:1216). The ribose-5-phosphate isomerase B has an amino acid sequence having at least 90% identity to an amino acid sequence selected from (SEQ ID NOs: 1213 to 2107) as available on WIPO website based on the Clustal W method of alignment using the default parameters of GAP PENALTY = 10, GAP LENGTH PENALTY = 0.1, and Gonnet 250 series of protein weight matrix (preferably the ribose-5-phosphate isomerase B has an amino acid sequence having at least 90% identity to an amino acid sequence selected from (SEQ ID NOs: 1213 to 1217) based on the Clustal W method of alignment using the default parameters). The polypeptide having xylose isomerase activity is a protein having an E-value score of less than or equal to 3x 10-10 when queried using a Profile HMM prepared using (SEQ ID NOs: 19, 21, 23, 25, 27, 29, 31, 33, 35, 37, 39, 41, 43, 45, 47, 49, 51, 53, 55, 57, 59, 61, 63, 65, 67, 69, 71, 73, 75, 77, 79, and 81) as available on WIPO website, and having 4 catalytic site residues of histidine 54, aspartic acid 57, glutamic acid 181, and lysine 183, with the position numbers in reference to the Streptomyces albus xylose isomerase sequence of (SEQ ID NO: 61). The xylose isomerase polypeptide has an amino acid sequence having at least 90% identity to an amino acid sequence selected from (SEQ ID NOs: 19, 21, 23, 25, 27, 29, 31, 33, 35, 37, 39, 41, 43, 45, 47, 49, 51, 53, 55, 57, 59, 61, 63, 65, 67, 69, 71, 73, 75, 77, 79, and 81) based on the Clustal W method of alignment using the default parameters of GAP PENALTY = 10, GAP LENGTH PENALTY = 0.1, and Gonnet 250 series of protein weight matrix. Preferred Process: In the process for producing ethanol, the ribose-5-phosphate isomerase activity is activity of a polypeptide selected from ribose-5-phosphate isomerase A and ribose-5-phosphate isomerase B. The medium comprises either a mixture of sugars including xylose or xylose as a sole sugar. Recombinant Methods (disclosed): The bacterial host cell (C1) is prepared by standard recombinant methods. EXAMPLE - Fermentation performance of Zymomonas mobilis ZW801-4 strain having increased expression of both xylose isomerase and ribulose-5-phosphate isomerase, was evaluated for ethanol production from xylose; as follows. A pZB188/aadA vector containing the E. coli xylose isomerase (XI) coding region (coding region (SEQ ID NO: 20) as available on WIPO website; (protein SEQ ID NO: 19) as available on WIPO website) with its transcription directed by a native Z. mobilis glyceraldehyde-3-phosphate dehydrogenase (GAP) promoter (pZB188/aadA-GapXylA (also called pZB188/aadA-641GapXylA); was used. The PgapXylA expression cassette (SEQ ID NO: 18) as available from WIPO website had GAP promoter (Pgap) from the ZW641 strain. Also, expression of extrachromosomal copy of a chimeric gene containing native Z. mobilis ribulose-5-phosphate isomerase (RPI-A) coding region as pZB-GI-RPI was accomplished by cloning coding region into shuttle vector adjacent to glucose isomerase (GI) promoter derived from Actinoplanes missouriensis. The shuttle vectors pZB-GI-RPI, and pZB188/aadA-641 GapXylA, were sequentially transformed into Z. mobilis strain ZW801-4. The strain containing RPI-A vector, and spectinomycin marker, was isolated first by transformation and selection on MRM3G5-spec plates. Transformed cells were isolated as single colonies and then re-transformed with xylA vector containing kanamycin resistance marker. Strains isolated from MRM3G5-KAN plates were shown to be both spectinomycin and kanamycin tolerant, and were referred to as xylA GI-rpiZ strains. Individual colonies containing the two plasmids (xylA/GI-rpiZ1.1 and xylA/GI-rpiZ1.2) were grown overnight in MRM3G10 medium with both spectinimycin (250 mu g/ ml) and kanamycin (400 mu g/ml). Control strains (ZW801-1 and ZW801-2) were grown in MRM3G10 medium with no antibiotic selection. Cells were then transferred to MRM3X10 medium and incubated for additional 20 hours at 30 degrees C. A final transfer to fresh MRM3X10 medium, at initial OD600 of 0.1, was done to minimize transfer of glucose from original culture into test medium. The ZW801 control strain, in duplicate, and xylA/GI-rpiZ strains were incubated at 30 degrees C and monitored for cell growth and sugar consumption by HPLC analysis. It was observed that strains with increased XI and RPI expression grew at increased rate and to higher final cell mass, relative to controls. An improved fermentation performance with increase in xylose use rate and final xylose amount consumed for strains carrying both xylA and RPI-A shuttle vectors was observed, with increased xylose use reflected increase in final ethanol titer, which was approximately 45 g/L at 96 hours (where the results for strains having pXylA-2, pXylA-4, pZB188-1, and pZB188-3, for ethanol production (g/L) were 32.26, 29.6, 43.67, and 45.17, respectively, at 91 hours). Thus combination of increased XI and RPI remedied detrimental effect of increased XI alone and further increased xylose utilization and ethanol production in high XI ZW801-4 strain.