Full text loading...
Chapter 14 : Periplasmic Nitrate Reduction
Category: Bacterial Pathogenesis; Microbial Genetics and Molecular Biology
Ebook: Choose a downloadable PDF or ePub file. Chapter is a downloadable PDF file. File must be downloaded within 48 hours of purchase
Before 1980, just two types of bacterial nitrate reductase were widely recognized: these were the soluble, cytoplasmic nitrate reductases involved in nitrate assimilation and the membrane-associated respiratory nitrate reductases. It rapidly became apparent that, in contrast to the more conserved components of the membrane-associated respiratory nitrate reductase encoded by the narGHJI operons, there were at least five levels of diversity among the periplasmic nitrate reductases: their distribution among bacteria of different physiological types; their regulation; their physiological roles; their components; and their genetic context. This chapter reviews each of these aspects followed by a summary of recent developments, including the realization by Richardson and his colleagues that there is a fourth type of nitrate reductase, a membrane-associated group with catalytic sites located in the periplasm, which might explain how the diversity of the Nap enzymes has evolved. Twelve different types of polypeptide are encoded by the various nap clusters, but only two of them, napA and napD, have so far always been found together. Further support for the ideas of Richardson and Jepson comes from the nap gene cluster in Anaeromyxobacter dehalogenans, which includes a gene encoding a small tetraheme c-type cytochrome homologous to NapM. Given that the sulfate:sulfite redox couple is strongly electronegative compared with the nitrate:nitrite couple, it would be fascinating to determine whether nitrate reduction by D. desulfuricans is repressed by sulfate.
Electron transfer to NapA in different bacteria.
Evolution of cytochrome c-linked periplasmic nitrate reductases.
Various physiological roles of Nap in different bacteria
Why an E. coli strain expressing a periplasmic nitrate reductase outcompetes a strain expressing only nitrate reductase A during nitrate-limited anaerobic growth a
Polypeptides encoded by nap gene clusters in various bacteria
Variety of combinations of genes in the nap clusters of different Shewanella strains a