Bacteroides spp. have an essential requirement for heme and non-heme iron. They cannot synthesize the tetrapyrrole macrocycle ring due to a lack of genes for the heme biosynthetic pathway. It is remarkable that heme-dependent organisms outnumber heme-independent organisms in the lower intestinal tract suggesting that heme biosynthesis is not essential for colonization of the colonic environment. However, this colonization advantage may be due to the fact that under anaerobic conditions in the presence of heme, B. fragilis can generate nearly the double amount of ATP than Escherichia coli per mol of glucose. This high energy yield is linked to a rudimentary heme-induced fumarate reductase and cytochrome b-dependent electron transport energy metabolism pathway which uses fumarate as the terminal electron acceptor. Moreover, Bacteroides spp. can incorporate iron-deuteroporphyrin and iron-mesoporphyrin into a functional type-b cytochrome. Heme can be demetalated without cleaving the tetrapyrrole ring releasing free iron and free protoporphirin IX. The ability of the opportunistic human pathogen B. fragilis to cause infections seems to be due in part to its ability to scavenge heme and iron from host proteins. The in-frame translated intergenic region of the fused FeoAB proteins are exclusively present in gastro-intestinal colonizers belonging to the Bacteroidetes, Firmicutes and Actinobacteria phyla. Several members of the Bacteroides group have three orthologs of the mammalian-type bacterial ferritin gene, ftnA. FtnA may play an important role in protection against iron-induced oxidative stress in this group of highly aerotolerant anaerobes.

Further reading: Iron Uptake and Homeostasis in Microorganisms

Labels: Bacteroides, Iron acquisition mechanisms, Iron transporters, Iron uptake in Bacteroides, Iron uptake systems, Iron-homeostasis, Iron-metabolism, Iron-uptake