Biochemical diversity among sulfur-dependent, hyperthermophilic microorganisms

Abstract

Hyperthermophiles are a recently discovered group of microorganisms that grow at and above 90°C. They currently comprise over 20 different genera, and except for two novel bacleria, all are classified as Archaea. The majority of these organisms are obligately anaerobic heterotrophs that reduce elemental sulfur (S °) to H2S. The best studied from a biochemical perspective are the archaeon, ~'rococcus furiosus, and the bacterium, Thermotoga rnaritirna, both of which are saccharolytic. P. furiosus is thought to contain a new type of Entner-Doudoroff pathway for the conversion of carbohydrates ultimately to acetate, H 2 and CO~. The pathway is independent of nicotinamide nucleotides and involves novel types of ferredoxin-linked oxidoreductases, one of which has tungsten, a rarely used element, as a prosthetic group. The only site of energy conservation is at the level of acetyl CoA, which in the presence of ADP and phosphate is converted to acetate and ATP in a single step. In contrast, 72 maritima utilizes a conventional Embden-Meyerhof pathway for sugar oxidation. P. furiosus also utilizes peptides as a sole carbon and energy source. Amino acid oxidation is thought to involve glutamate dehydrogenase together with at least three types of novel ferredoxin-linked oxidoreductases which catalyze the oxidation of 2-ketoglutarate, aryl pyruvates and formaldehyde. One of these enzymes also utilizes tungsten. In P. furiosus, virtually all of the reductant that is generated during the catabolism of both carbohydrates and peptides is channeled to a cytoplasmic hydrogenase. This enzyme is now termed sulhydrogenase, as it reduces both protons to H 2 and S ° (or polysulfide) to H2S. S ° reduction appears to lead to the conservation of energy in P. furiosus but not in 72 rnaritima, although the mechanism by which this occurs is not known.

Effects of elemental sulfur on the metabolism of the deep-sea hyperthermophilic archaeon Thermococcus strain ES-1: characterization of a sulfur-regulated, non-heme iron alcohol dehydrogenase

“…We have previously characterized several enzymes involved in the primary metabolic pathways of two other heterotrophic hyperthermophiles, Thermococcus litoralis (T max , 98ЊC [50]) and P. furiosus (1,2). However, in contrast to these organisms, ES-1 does not utilize carbohydrates and, as we show herein, is obligately dependent upon S 0 reduction for growth.…”

“…Hyperthermophiles are a recently discovered group of microorganisms that have the remarkable property of growing at temperatures of 90ЊC and above (1,2,64,65). They have been isolated from a variety of geothermally heated environments, and almost all are classified as Archaea (formerly Archaeobacteria [75]).…”

“…The initial objectives of this study were therefore (i) to examine ES-1 for the activities of a variety of enzymes previously detected in P. furiosus and T. litoralis that are postulated to be involved in peptide utilization and reductant generation and (ii) to determine if any of the activities were affected by S 0 limitation. Among the enzymes of interest were formaldehyde ferredoxin oxidoreductase (FOR) (48), aldehyde ferredoxin oxidoreductase (AOR) (47) (2,44), and branched-chain keto acids (2,29).…”

Gene expression and characterization of two 2‐oxoacid:ferredoxin oxidoreductases from Aeropyrum pernix K1

“…2-Oxoacid:ferredoxin oxidoreductase (OFOR) is a key enzyme catalyzing coenzyme A-dependent oxidative decarboxylation of 2-oxoacids, such as pyruvate (POR) [1][2][3][4][5][6], 2-oxoisovalerate (VOR) [6,7], 2-oxoglutarate (a-keto-glutarate) (GOR or KOR) [6,8], and indole pyruvate (IOR) [6,9]. OFOR uses ferredoxin as an electron acceptor instead of NAD + , which is adopted as an electron acceptor in the 2-oxoacid dehydrogenase multienzyme complexes in most living organisms.…”

Characterization of aromatic aminotransferases from the hyperthermophilic archaeon Thermococcus litoralis

“…Some are also able to utilize certain carbohydrates as a carbon source and a novel pathway for carbohydrate metabolism has been proposed [6][7][8]. The pathways of peptide utilization are less understood.…”