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Applied and Environmental Microbiology, December 2007, p. 7819-7825, Vol. 73, No. 24
0099-2240/07/$08.00+0     doi:10.1128/AEM.01919-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Riboflavin Biosynthesis Is Associated with Assimilatory Ferric Reduction and Iron Acquisition by Campylobacter jejuni{triangledown}

Rachel A. Crossley,1 Duncan J. H. Gaskin,1 Kathryn Holmes,1,{dagger} Francis Mulholland,1 Jerry M. Wells,1,§ David J. Kelly,2 Arnoud H. M. van Vliet,1* and Nicholas J. Walton1

Institute of Food Research, Norwich Research Park, Colney Lane, Norwich NR4 7UA, United Kingdom,1 Department of Molecular Biology and Biotechnology, University of Sheffield, Sheffield S10 2TN, United Kingdom2

Received 21 August 2007/ Accepted 19 October 2007

One of the pathways involved in the acquisition of the essential metal iron by bacteria involves the reduction of insoluble Fe3+ to soluble Fe2+, followed by transport of Fe2+ to the cytoplasm. Flavins have been implicated as electron donors in this poorly understood process. Ferrous iron uptake is essential for intestinal colonization by the important pathogen Campylobacter jejuni and may be of particular importance under low-oxygen conditions. In this study, the links among riboflavin biosynthesis, ferric reduction, and iron acquisition in C. jejuni NCTC11168 have been investigated. A riboflavin auxotroph was generated by inactivation of the ribB riboflavin biosynthesis gene (Cj0572), and the resulting isogenic ribB mutant only grew in the presence of exogenous riboflavin or the riboflavin precursor diacetyl but not in the presence of the downstream products flavin adenine dinucleotide and flavin mononucleotide. Riboflavin uptake was unaffected in the ribB mutant under iron-limited conditions but was lower in both the wild-type strain and the ribB mutant under iron-replete conditions. Mutation of the fur gene, which encodes an iron uptake regulator of C. jejuni, resulted in an increase in riboflavin uptake which was independent of the iron content of the medium, suggesting a role for Fur in the regulation of the as-yet-unknown riboflavin transport system. Finally, ferric reduction activity was independent of iron availability in the growth medium but was lowered in the ribB mutant compared to the wild-type strain and, conversely, increased in the fur mutant. Taken together, the findings confirm close relationships among iron acquisition, riboflavin production, and riboflavin uptake in C. jejuni.

* Corresponding author. Mailing address: Institute of Food Research, Office E410, Norwich Research Park, Colney Lane, Norwich NR4 7UA, United Kingdom. Phone: 44-1603-255250. Fax: 44-1603-255288. E-mail: arnoud.vanvliet{at}bbsrc.ac.uk

{triangledown} Published ahead of print on 26 October 2007.

{dagger} Present address: Trinity College, Adelaide and Meath Hospital, Dublin, Ireland.

§ Present address: Animal Sciences Department, Wageningen University, Wageningen, The Netherlands.

Applied and Environmental Microbiology, December 2007, p. 7819-7825, Vol. 73, No. 24
0099-2240/07/$08.00+0     doi:10.1128/AEM.01919-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.



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