Abstract
One of the pathways involved in the acquisition of the essential metal iron by bacteria involves the reduction of insoluble Fe
3+
to soluble Fe
2+
, followed by transport of Fe
2+
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
.