Caloramator boliviensis sp. nov., a thermophilic, ethanol-producing bacterium isolated from a hot spring

Abstract

A novel moderately thermophilic, anaerobic, ethanol-producing bacterial strain, 45B T , was isolated from a mixed sediment water sample collected from a hot spring at Potosi, Bolivia. The cells were straight to slightly curved rods approximately 2.5 mm long and 0.5 mm wide. The strain was Gramstain-variable, spore-forming and monotrichously flagellated. Growth of the strain was observed at 45-65 6C and pH 5.5-8.0, with optima of 60 6C and pH 6.5. The substrates utilized by strain 45B T were xylose, cellobiose, glucose, arabinose, sucrose, lactose, maltose, fructose, galactose, mannose, glycerol, xylan, carboxymethylcellulose and yeast extract. The main fermentation product from xylose and cellobiose was ethanol (0.70 and 0.45 g ethanol per gram of consumed sugar, respectively). Acetate, lactate, propionate, carbon dioxide and hydrogen were also produced in minor quantities. 1,3-Propanediol was produced when glycerol-containing medium was supplemented with yeast extract. The major cellular fatty acids were anteiso-C 15 : 0 , C 16 : 0 , iso-C 16 : 0 , C 15 : 1 , iso-C 14 : 0 , C 13 : 0 and C 14 : 0 . The polar lipids diphosphatidylglycerol, phosphatidylglycerol, phosphatidylethanolamine, an aminoglycolipid and 15 other unidentified lipids were predominant. The DNA G+C content of strain 45BT was 32.6 mol%. Phylogenetic analysis based on 16S rRNA gene sequence similarity revealed that strain 45B T is located within the Gram-type positive Bacillus-Clostridium branch of the phylogenetic tree. On the basis of morphological and physiological properties and phylogenetic analysis, strain 45B T represents a novel species, for which the name Caloramator boliviensis sp. nov. is proposed; the type strain is 45B T (5DSM 22065Growing concerns on environmental issues and finite fossil fuel supplies have stimulated an increasing interest in microbial fuel ethanol production using renewable raw materials (Olsson & Hahn-Hagerdal, 1996;Wheals et al., 1999;Wyman, 1999 During the last two decades, saccharolytic, thermophilic, anaerobic bacteria have been intensively studied because of their potential for producing ethanol by metabolizing a very broad range of carbohydrates, including pentose sugars and their polymers. In addition, the thermophilic fermentation process has important advantages such as easier product recovery, minimized contamination risk, reduced costs of pumping and stirring, and no aeration and cooling problems (Cook & Morgan, 1994;Wiegel et al., 1985).Some thermophilic anaerobic clostridia from clusters III, V and VII (according to the phylogenetic interrelationship established by Collins et al., 1994) have been reported to produce ethanol at high temperatures. Moreover, some other clostridial species that are phylogenetically distinct but conserve some physiological similarities have been reclassified in separate genera, including the genus Caloramator.Members of the Caloramator/Thermobrachium genera also produce ethanol, short chain fatty acids, carbon dioxide and hydrogen as end products of glucose fermentation (...

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