Chemolithotrohic Bacteria: Distributions, Functions and Significance in Volcanic Environments

Abstract

A mosaic of environments comprises most volcanic ecosystems. Whether terrestrial or submarine, many of these environments contain large deposits of reduced minerals, or experience large fluxes of reduced substrates, especially sulfur-containing compounds. These systems, which also are typically characterized by temperature and pH extremes, have yielded a rich variety of chemolithotrophic bacteria, and contributed much to our understanding of chemolithotroph ecology and physiology. However, volcanic ecosystems also consist of environments where inorganic and organic substrates are limiting. In these cases, chemolithotrophs may still play important roles by scavenging carbon monoxide, hydrogen or both. These gases can support metabolism of facultative chemolithotrophs, a functional group that includes many nitrogen-fixing bacteria. Facultative chemolithotrophs may not only represent important early colonists on fresh volcanic substrates (e.g., basalts lacking sulfides), they may also contribute significantly to ecosystem succession through nitrogen fixation and interactions with vascular plants. Analyses of CO and hydrogen consumption by recent deposits on Kilauea volcano show that both substrates support significant activity, while molecular approaches show a high diversity of lithotrophs. Collectively, these and other observations indicate that chemolithotrophic metabolism is more widespread than generally acknowledged, and likely to play fundamental roles in shaping ecosystem dynamics.