Summary auto-generated
Researchers isolated Geoglobus ahangari, a novel hyperthermophilic archaeon from a deep-sea hydrothermal vent at Guaymas Basin. This coccoid-shaped, strictly anaerobic microorganism grows optimally at 88°C and represents the first Fe(III)-reducing hyperthermophile capable of autotrophic growth on hydrogen without organic carbon requirements. The isolate can oxidize hydrogen, short-chain fatty acids (pyruvate, acetate, formate), and remarkably, long-chain fatty acids (palmitate, stearate) with Fe(III) oxide as the sole electron acceptor. Notably, it requires only poorly crystalline Fe(III) oxide for electron acceptance and cannot utilize other electron acceptors including sulfate, nitrate, or oxygen. The organism was isolated using a novel technique employing insoluble Fe(III) oxide in solidified medium. With a G+C content of 58.7 mol%, 16S rDNA analysis places it closest to Archaeoglobus species (96% similarity) but sufficiently distinct to warrant a new genus designation. The discovery of long-chain fatty acid oxidation at hyperthermophilic temperatures and Fe(III)-coupled autotrophic hydrogen utilization significantly expands understanding of ancient and extreme environment metabolisms.
Key findings
- G. ahangari is the first hyperthermophile capable of autotrophic growth on hydrogen with Fe(III) as sole electron acceptor, requiring no organic carbon
- The organism can oxidize long-chain fatty acids (palmitate and stearate) anaerobically coupled to Fe(III) reduction, a capability not previously observed in hyperthermophiles
- It utilizes only poorly crystalline Fe(III) oxide as electron acceptor; other acceptors including sulfate, nitrate, oxygen, and sulfite do not support growth
- The use of insoluble Fe(III) oxide in isolation medium proved crucial for recovery, enabling discovery of metabolic capabilities distinct from previously characterized Fe(III) reducers
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Abstract
A novel, regular to irregular, coccoid-shaped, anaerobic, Fe(III)-reducing micro-organism was isolated from the Guaymas Basin hydrothermal system at a depth of 2000 m. Isolation was carried out with a new technique using Fe(III) oxide as the electron acceptor for the recovery of colonies on solid medium. The isolate, designated strain 234(T), was strictly anaerobic and exhibited a tumbling motility. The cells had a single flagellum. Strain 234(T) grew at temperatures between 65 and 90 degrees C, with an optimum at about 88 degrees C. The optimal salt concentration for growth was around 19 g l(-1). The isolate was capable of growth with H(2) as the sole electron donor coupled to the reduction of Fe(III) without the need for an organic carbon source. This is the first example of a dissimilatory Fe(III)-reducing micro-organism capable of growing autotrophically on hydrogen. In addition to molecular hydrogen, strain 234(T) oxidizes pyruvate, acetate, malate, succinate, peptone, formate, fumarate, yeast extract, glycerol, isoleucine, arginine, serine, glutamine, asparagine, stearate, palmitate, valerate, butyrate and propionate with the reduction of Fe(III). This isolate is the first example of a hyperthermophile capable of oxidizing long-chain fatty acids anaerobically. Isolate 234(T) grew exclusively with Fe(III) as the sole electron acceptor. The G+C content was 58.7 mol%. Based on detailed analysis of its 16S rDNA sequence, G+C content, distinguishing physiological features and metabolism, strain 234(T) is proposed to represent a novel genus within the Archaeoglobales. The name proposed for strain 234(T) is Geoglobus ahangari gen. nov., sp. nov.