Life in hot acid: a genome-based reassessment of the archaeal orderSulfolobales

The orderSulfolobaleswas one of the first named Archaeal lineages, with globally distributed members from terrestrial thermal acid springs (pH < 4;T> 65 degrees C). TheSulfolobalesrepresent broad metabolic capabilities, ranging from lithotrophy, based on inorganic iron and sulfur biotransformations, to autotrophy, to chemoheterotrophy in less acidophilic species. Components of the 3-hydroxypropionate/4-hydroxybutyrate carbon fixation cycle, as well as sulfur oxidation, are nearly universally conserved, although dissimilatory sulfur reduction and disproportionation (Acidianus,StygiolobusandSulfurisphaera) and iron oxidation (Acidianus,Metallosphaera,Sulfurisphaera,SulfuracidifexandSulfodiicoccus) are limited to fewer lineages. Lithotrophic marker genes appear more often in highly acidophilic lineages. Despite the presence of facultative anaerobes and one confirmed obligate anaerobe, oxidase complexes (fox,sox,doxand a new putative cytochrome bd) are prevalent in many species (even facultative/obligate anaerobes), suggesting a key role for oxygen among theSulfolobales. The presence offoxgenes tracks with a putative antioxidant OsmC family peroxiredoxin, an indicator of oxidative stress derived from mixing reactive metals and oxygen. Extreme acidophily appears to track inversely with heterotrophy but directly with lithotrophy. Recent phylogenetic re-organization efforts are supported by the comparative genomics here, although several changes are proposed, including the expansion of the genusSaccharolobus.

Automated summary

The Sulfolobales lineage is diverse in metabolic capabilities, with lithotrophy, autotrophy, and chemoheterotrophy being common. Despite some lineages carrying out sulfur reduction and disproportionation as well as iron oxidation, lithotrophic marker genes are more prevalent in highly acidophilic species, and extreme acidophily appears to be inversely related to heterotrophy.