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Journal of Bacteriology, October 2008, p. 6615-6624, Vol. 190, No. 20
0021-9193/08/$08.00+0     doi:10.1128/JB.00815-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

The yiaKLX1X2PQRS and ulaABCDEFG Gene Systems Are Required for the Aerobic Utilization of L-Ascorbate in Klebsiella pneumoniae Strain 13882 with L-Ascorbate-6-Phosphate as the Inducer{triangledown}

Evangelina Campos, Lucia de la Riva, Fernando Garces, Rosa Giménez, Juan Aguilar,* Laura Baldoma, and Josefa Badia

Department of Biochemistry and Molecular Biology, Institut de Biomedecina de la Universitat de Barcelona(IBUB), Faculty of Pharmacy, University of Barcelona, Barcelona, Spain

Received 10 June 2008/ Accepted 5 August 2008

The capacity to both ferment and oxidize L-ascorbate has been widely documented for a number of enteric bacteria. Here we present evidence that all the strains of Klebsiella pneumoniae tested in this study ferment L-ascorbate using the ula regulon-encoded proteins. Under aerobic conditions, several phenotypes were observed for the strains. Our results showed that the yiaK-S system is required for this aerobic metabolic process. Gel shift experiments performed with UlaR and YiaJ and probes corresponding to the specific promoters indicated that L-ascorbate-6-phosphate is the effector molecule recognized by both regulators, since binding of the repressors to their recognition sites was impaired by the presence of this compound. We demonstrated that in K. pneumoniae cells L-ascorbate-6-phosphate is formed only by the action of the UlaABC phosphotransferase system. This finding explains why strains that lack the ula genetic system and therefore are unable to form the inducer intracellularly cannot efficiently use this vitamin as a carbon source under either anaerobic or aerobic conditions. Thus, efficient aerobic metabolism of L-ascorbate in K. pneumoniae is dependent on the presence of both the yiaK-S and ula systems. The expression of the yiaK-S operon, but not the expression of the ula regulon, is controlled by oxygen availability. Both systems are regulated by the cyclic AMP (cAMP)-cAMP receptor protein (CRP) complex and by IHF.

* Corresponding author. Mailing address: Departamento de Bioquímica, Facultad de Farmacia, Universidad de Barcelona, Avda. Diagonal 643, 08028 Barcelona Spain. Phone: 34 93 403 4496. Fax: 34 93 402 4520. E-mail: juanaguilar{at}ub.edu

{triangledown} Published ahead of print on 15 August 2008.

Journal of Bacteriology, October 2008, p. 6615-6624, Vol. 190, No. 20
0021-9193/08/$08.00+0     doi:10.1128/JB.00815-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.





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