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Journal of Bacteriology, July 2007, p. 4800-4808, Vol. 189, No. 13
0021-9193/07/$08.00+0     doi:10.1128/JB.01895-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

L-Sorbose Reductase and Its Transcriptional Regulator Involved in L-Sorbose Utilization of Gluconobacter frateurii{triangledown}

Wichai Soemphol,1 Hirohide Toyama,1,2* Duangtip Moonmangmee,3 Osao Adachi,1 and Kazunobu Matsushita1

Department of Biological Chemistry, Faculty of Agriculture,1 Applied Molecular Bioscience, Graduate School of Medicine, Yamaguchi University, Yamaguchi 753-8515, Japan,2 Department of Microbiology, Faculty of Science, King Mongkut's University of Technology Thonburi, Prachauthit Road, Tungkru, Bangkok 10140, Thailand3

Received 15 December 2006/ Accepted 19 April 2007

Upstream of the gene for flavin adenine dinucleotide (FAD)-dependent D-sorbitol dehydrogenase (SLDH), sldSLC, a putative transcriptional regulator was found in Gluconobacter frateurii THD32 (NBRC 101656). In this study, the whole sboR gene and the adjacent gene, sboA, were cloned and analyzed. sboR mutation did not affect FAD-SLDH activity in the membrane fractions. The SboA enzyme expressed and purified from an Escherichia coli transformant showed NADPH-dependent L-sorbose reductase (NADPH-SR) activity, and the enzyme was different from the NADPH-SR previously reported for Gluconobacter suboxydans IFO 3291 in molecular size and amino acid sequence. A mutant defective in sboA showed significantly reduced growth on L-sorbose, indicating that the SboA enzyme is required for efficient growth on L-sorbose. The sboR mutant grew on L-sorbose even better than the wild-type strain did, and higher NADPH-SR activity was detected in cytoplasm fractions. Reverse transcription-PCR experiments indicated that sboRA comprises an operon. These data suggest that sboR is involved in the repression of sboA, but not in the induction of sldSLC, on D-sorbitol and that another activator is required for the induction of these genes by D-sorbitol or L-sorbose.

* Corresponding author. Mailing address: Department of Biological Chemistry, Faculty of Agriculture, Yamaguchi University, Yamaguchi 753-8515, Japan. Phone and fax: 81-83-933-5859. E-mail: hirot{at}yamaguchi-u.ac.jp

{triangledown} Published ahead of print on 27 April 2007.

Journal of Bacteriology, July 2007, p. 4800-4808, Vol. 189, No. 13
0021-9193/07/$08.00+0     doi:10.1128/JB.01895-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.





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