Hyperthermophile-Metal Interactions in Hydrothermal Environments

Abstract

This chapter explores the metal chemistry of different types of marine hydrothermal environments, the metal requirements of hyperthermophiles, the nature and constraints of their interactions with metals, and the biogeochemical implications of hyperthermophile-metal interactions. Metalloenzymes form a major part of metalloproteomes and reflect the bioavailability of metals within a given environment that are (or were at some point during their evolution) the most accessible. Dissimilatory iron reduction has been studied extensively in just four groups of hyperthermophilic archaea and one hyperthermophilic bacterium. The reduction potential and pH of an environment also appear to affect the growth rates of hyperthermophiles on iron. It is clear that there is extensive interaction between metals and hyperthermophilic microbes from hydrothermal environments, and yet the study of the nature of these interactions is in its infancy. Dissimilatory metal reduction may be limited by the organism’s ability to transfer electrons from its cytoplasm to the typically insoluble metal acceptor. Therefore, it is necessary to determine the respiratory mechanisms and how they lead to energy conservation, especially because the physiological mechanisms for metal reduction in hyperthermophiles differ from those found in mesophilic bacteria based on the lack of polyheme c-type cytochromes, a periplasm, and an outer cell wall membrane. Further study of hyperthermophilemetal interactions in hydrothermal environments will create a new understanding of the basic principles that govern a broad array of metabolic processes and a significant portion of the Earth’s biosphere.