Sunday, July 29, 2007
P35

Isolation of an operon involved in xylitol metabolism from Pantoea ananatis

Yoshikiyo Sakakibara, National Food Research Institute, 2-1-12 Kannondai, Tsukuba, Japan and Badal C. Saha, Fermentation Biotechnology Research Unit, National Center for Agricultural Utilization Research, USDA-ARS, 1815 N. University Street, Peoria, IL 61604.

An operon involved in xylitol metabolism in a xylitol-utilizing Pantoea ananatis mutant was cloned by the transposon tagging method.  Sequencing analysis revealed that seven consecutive open reading frames (ORFs) are located in the same strand (xytA-G).  Sequence homology search suggested that the operon encoded two oxidoreductases belonging to the short-chain dehydrogenase/reductase family, three subunits constituting ATP-binding cassette (ABC) transporter and two proteins of unknown function.  Both oxidoreductases were heterologously expressed in E. coli to test activity on pentitols.  Consequently, one of the oxidoreductases converted xylitol to L-xylulose, which is identified as L-xylulose reductase.  The other oxidoreductase, of which natural substrates remain unknown did not oxidize xylitol but oxidized L-arabitol.  Another ORF (xytR) was found upstream of the operon in the opposite strand and predicted to encode a DeoR-type transcriptional regulator.  In the xylitol-utilizing mutant, single nucleotide substitution that caused a nonsense mutation was found in the xytR, suggesting the product of xytR negatively controls expression of the operon.

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