Microbial metal-ion reduction and Mars: extraterrestrial expectations?

• Published in: Current Opinion in Microbiology Vol. 5; no. 3; pp. 296 - 300
• Main Authors: Nealson, Kenneth H., Cox, B.Lea
• Format: Book Review Journal Article
• Language: English
• Published: England Elsevier Ltd 01.06.2002
• Subjects: Bacteria - chemistry; bioremediation; dissimilatory metal-ion-reducing bacteria; DMRB; extracellular electron shuttles; Extraterrestrial Environment; Mars; metal ion reduction; Metals - chemistry; Oxidation-Reduction; Mars; dissimilatory metal-ion-reducing bacteria; bioremediation; Microbiology; DMRB; metal ion reduction; extracellular electron shuttles
• ISSN: 1369-5274; 1879-0364
• DOI: 10.1016/S1369-5274(02)00326-0

Dissimilatory metal-ion-reducing bacteria (DMRB) can couple the reduction of a variety of different metal ions to cellular respiration and growth. The excitement of this metabolic group lies not only in the elucidation of a new type of metabolism, but also in the potential use of these abilities for the removal of toxic organics, and in their ability to reduce (and thus, detoxify) other toxic metals, such as U(VI) and Cr(VI). This review focuses on recent advances in the study of DMRB, including the use of external electron shuttles to enhance rates of metal reduction; genome sequencing and consequent genomic and proteomic analyses; new imaging approaches for high resolution analysis of both cells and chemical components; the demonstration of fractionation of stable isotopes of iron during iron reduction; and the elucidation of the types and patterns of secondary mineral formation during metal reduction. One of the secondary minerals is magnetite, the subject of intense controversy regarding the possibility of evidence for life from the Martian meteorite ALH84001. This review thus ends with a short consideration of the evidence for magnetic ‘proof’ of the existence of past life on Mars. Metal-ion-reducing microbes 'breathe rocks', giving us a new perspective on the versatility of life, creating isotopic signatures in the process, and depositing secondary minerals that may be of use as biosignatures.