The Worth of Coppers

Abstract

Microbiology The immense reach of microbial sequencing projects has outstripped the capacity of physiology (with its reliance on cultivatable organisms) and biochemistry (ditto for purified enzymes) to exploit these data sets—apart from exceptional efforts, of which the discovery of a fourth pathway for oxygen evolution by Ettwig et al. is the most recent. Using comparative bioinformatics and a bit of old-fashioned guesswork, Walker et al. provide a plausible picture of the lifestyle of the marine archeon Nitrosopumilus maritimus . It falls into a class of microbes that oxidize ammonia to hydroxylamine and thence to nitrite. Doing so yields hydrogen ions and electrons. Unlike ammonia-oxidizing bacteria that depend on heme(iron)-based proteins for the chemical and electron transfer reactions, Nitrosopumilus hews to a copper-based economy, encoding several varieties of multicopper oxidases and plastocyanin-like carriers. This apparent relief from a heavy dependence on iron, coupled to the high affinity of its ammonia monooxygenase and energy-efficient mode of carbon fixation, may account for its ecological success. Nature 464 , 543 (2010); Proc. Natl. Acad. Sci. U.S.A. 107 , 10.1073/pnas.0913533107 (2010).