Microbial Metabolism of Nickel

This chapter summarizes the multiple processes that microorganisms use to metabolize nickel ions and describes nickel-dependent enzymatic transformations. A wide variety of microbial species sense and respond to nickel ion concentrations by synthesizing nickel-specific transcription factors, and a few possess nickel-responsive riboswitches. During nickel deficiency, some microbes are capable of taking up this micronutrient using influx systems that include ATP binding cassette transporters and secondary transporters such as permeases. Certain microorganisms eliminate excess concentrations of internal nickel ions by using nickel-specific cation diffusion facilitators, major facilitator protein superfamily members, P-type ATPases, and other efflux systems. The basis of nickel toxicity and several mechanisms of nickel resistance also are described in this chapter. Many microorganisms utilize nickel, variously incorporating it into glyoxalase I, acireductone dioxygenase, quercetin 2,4-dioxygenase, superoxide dismutase, urease, [NiFe] hydrogenase, carbon monoxide dehydrogenase, the acetyl-coenzyme A synthase/decarbonylase complex, 2-hydroxyacid racemases and epimerases, and methyl-S-coenzyme M reductase. Auxiliary proteins often function during the biosynthesis of nickel enzymes by delivering the nickel ion, synthesizing a nickel-containing organometallic cofactor, coupling the energy of nucleotide hydrolysis to the metal incorporation, or acting in other ways. Nickel storage proteins are present in some microorganisms. In sum, the microbial metabolism of nickel involves a rich landscape of biological processes.