The Electron Transport System of an Extremely Thermophilic Bacterium

Abstract

Active, membrane-bound NADH and succinate oxidase activities with a temperature optimum of 75 "C were demonstrated in an extremely thermophilic bacterium. These were relatively stable in cell-free extracts and respiratory particles at 75 "C, but at 90 "C the half-lives of these oxidase systems were about 15 min in respiratory particles and 80 min in cell-free extracts. The stability of the NADH oxidase in respiratory particles at 90 "C was enhanced by 2 M-(NH,),SO,, 50% (v/v) glycerol and by NADH. A number of other substrates were oxidized by the electron transport system. Respiratory particles contained cytochromes a-613, a-602, b-559, cytochrome o and at least one c-type cytochrome, c-555. The soluble fraction contained at least two c-type cytochromes, at least one of which was CO-reactive. The sensitivity of NADH and succinate oxidases to a range of inhibitors was determined. I N T R O D U C T I O NInterest in micro-organisms living in extreme thermal environments has increased over the past few years (see, for example, Brock, 1967 ;Williams, 1975) and a number of enzymes from extreme thermophiles have been characterized (see, for example, Campbell & Pace, 1968;Singleton & Amelunxen, 1973;Zuber, 1976;Ljungdahl & Sherod, 1976). Despite interest in the membrane composition of such organisms (Ray et al., 1971 a, b;Jackson et al., 1973 a), little is known about their electron transport systems (Pask-Hughes & Williams, 1975;McFetters & Ulrich, 1972). In this paper we describe the electron transport system of a thermophilic bacterium isolated from the Rotorua thermal region of New Zealand. The organism was Thermus-like (H. Morgan, personal communication) and, pending the final results of taxonomic work, it will be referred to as Thermus T351. The electron transport system (this paper) and other physiological and biochemical activities (H. Morgan & D. A. Cowan, personal communication) displayed optimal activity between 70 and 80 "C and negligible activity below 40 "C. The organism can therefore be described as caldoactive (Heinen & Heinen, 1972 ;Williams, 1975) or extremely thermophilic. M E T H O D SOrganism. Thermus T351 was isolated from a hot pool (79 k 4 "C), low in sulphide, at pH 7.8. The organism grew well at 75 "C at pH 7.5 to 7.8, but grew poorly below 60 "C; it was obligately aerobic. Cells were Gram-negative, non-motile, non-sporulating rods.

Caldolase, a chelator-insensitive extracellular serine proteinase from a Thermus spp

“…Thermus strain Tok3 was isolated from the Tokaanu thermal region, New Zealand. Cells were grown aerobic-ally at 75°C on Thermus medium (Hickey & Daniel, 1979). Large-scale growth (600 litres) of Thermus strain Tok3 was carried out in an 800-litre fermenter.…”

Comparative study of energy-transducing properties of cytoplasmic membranes from mesophilic and thermophilic Bacillus species

“…The respiratory chains of thermophilic species, consisting of highly organized multienzyme systems, such as dehydrogenases, electron carriers, and terminal oxidoreductases, have been investigated in terms of their redox carrier composition, activity, and sensitivity to classical inhibitors of electron transfer (6,9). Also, energy-transducing proper-* Corresponding author.…”

Isolation and characterisation of two chymotrypsins fromAllocyttus niger(black oreo dory) viscera

“…They concluded that this activation is too slow to be caused entirely by kinetic dissociation and that it may involve some proteolytic cleavage. The phenomenon of heat-induced activation has also been detected in enzymes other than proteases (Hickey & Daniel 1979). The stability profiles of chymotrypsins from rainbow trout show a similar tendency but they displayed maximal activity after 30 min incubation at temperatures of c. 30 and 40°C (Kristjansson & Nielsen 1991).…”