TECHNOLOGY FOCUS - BIOTECHNOLOGY - Preparation: (I) is produced by transforming an appropriate host strain suitable for preparing DNA for transformation of ATCC 31821 or its derivative with plasmid DNA, preparing DNAs from the methylation deficient host which is defective in DNA cytosine methylation (dcm) and/or DNA adenine methylase (dam), transforming the ATCC 31821 strain or its derivative with the prepared DNA, and selecting the transformants using a selection marker and/or analyzing the correct size of the DNA from the transformants (claimed).Preferred Strain: (I) is Z. mobilis ATCC 31821/pZB5. EXAMPLE - Xylose-fermenting Zymomonas mobilis was developed by transforming of the strain of Z. mobilis CP4 using plasmids, pZB5 and pZB4, which contains 4 xylose-metabolizing genes Pictaggio et al., U.S. Pat. No. 5514583. To obtain better xylose-fermenting Z. mobilis, several other Z. mobilis strains, ATCC31821, ATCC39676, and NRRL B14023 were tested to see whether these strains can be transformed by the vector plasmid, pZB186, which was used to construct xylose-fermenting plasmids. The plasmid DNA of pZB186 was prepared from the strain of Escherichia coli DH5alpha. An electroporation procedure was used for transformation. After electroporation, the cells were allowed to recover. Transformants containing pzB186 arose in the same medium additionally containing 1.5% agar and tetracycline (Tc)(20 micrograms/ml) (mating plate) following anaerobic incubation. The transformation frequency was calculated by CFU (number of transformants)/micrograms DNA. Strains ATCC39676 and NRRL B14023 were transformed at a relative high frequency (about 2-6 x 10 (to the power of 3) CFU/micrograms DNA) while strain ATCC31821 was transformed at a very low frequency (about 1 CFU/micrograms DNA or less). The xylose-fermenting plasmids, pZB4 and pZB5, were used to transform strains ATCC39676 and NRRL B14023 by electroporation. Although the transformation frequency of these two strains using the xylose-fermenting plasmids was reduced dramatically as compared to the vector plasmid, several transformants of 39676/pZB4, 39676/pZB5, B14023/pZB4 and B14023/pZB5, were obtained by isolating the tetracycline resistant colonies from the matting plates. The restriction analyses of the plasmid DNA from tetracycline-resistant transformants revealed that only a few transformants contained the correct plasmids. These transformants were further selected for their growth in a liquid RMX medium. The strains that grew well in the medium were designated as 39676/pZB4, 39676/pZB5, B14023/pZB4 and B14023/pZB5, respectively. All the strains performed comparable to the prior reported strain CP4/pZB5. The same xylose-fermenting plasmids, pZB4 and pZB5, were used to transform strains ATCC31821. No transformant was obtained using DNA prepared from E. coli DH5alpha after more than 10 trials of transformation. Several methods, including using various growth conditions, electroporating media and conditions were tried to improve the transformability of strain ZM4. The best conditions yielded about 20 transformants/micrograms DNA of pZB186. When using DNA purified from Z. mobilis CP4 or B14023 it was found that there was about a 100-fold increase of the transformation frequency. Consequently, plasmid DNA of pZB4 and pZB5 were prepared from Z. mobilis CP4. A few Tc resistance transformants were obtained from 4-5 trials of transformation. But only smaller plasmids that resulted from deletion were detected by restriction analyses of the plasmid DNA from Tc-resistant ZM4 transformants. After more than 10 trials of transformation using both pZB4 and pZB5, one Tc resistant ZM4 transformant was found to have the correct size of pZB5. Cells of this Tc resistant transformant was plated on RMX containing 20 micrograms/ml of Tc. Several colonies arose after incubation and one of them exhibited the best fermentation performance of xylose to ethanol and was isolated and designated as 31821/pZB5.