Buchnera gen. nov. and Buchnera aphidicola sp. nov., a Taxon Consisting of the Mycetocyte-Associated, Primary Endosymbionts of Aphids

Abstract

On the basis of three isolates (strains FC6^T [T = type strain], FC4, and RG1) of extremely thermophilic chemolithoautotrophic archaebacteria obtained from solfataric fields on ão Miguel Island, Azores, the new genus Stygiolobus is described. These isolates grow obligately chemolithotrophically by reduction of S⁰ with H₂ (H₂-S⁰ lithotrophy) and are the first strictly anaerobic members of the order Sulfolobales. With a DNA G+C content of 38 mol%, the Stygiolobus isolates resemble Sulfolobus spp., which, however, are faculatively organotrophic and aerobic S⁰ oxidizers. The new isolates are also distinct from Acidianus spp., which resemble Stygiolobus by growing by H₂-S⁰ lithotrophy. However, Acidianus spp. can also grow aerobically by S⁰ oxidation and have G+C contents of 31 mol%. At this time, only one species of the genus Stygiolobus is known, Stygiolobus azoricus sp. nov.; the type strain of S. azoricus is strain FC6 (= DSM 6296).