Thermoanaerobacter tengcongensis is a rod-shaped, gram-negative, anaerobic eubacterium that was isolated from a freshwater hot spring in Tengchong, China. Using a whole-genome-shotgun method, we sequenced its 2,689,445-bp genome from an isolate, MB4T (Genbank accession no. AE008691). The genome encodes 2588 predicted coding sequences (CDS). Among them, 1764 (68.2%) are classified according to homology to other documented proteins, and the rest, 824 CDS (31.8%), are functionally unknown. One of the interesting features of the T. tengcongensis genome is that 86.7% of its genes are encoded on the leading strand of DNA replication. Based on protein sequence similarity, the T. tengcongensis genome is most similar to that of Bacillus halodurans, a mesophilic eubacterium, among all fully sequenced prokaryotic genomes up to date. Computational analysis on genes involved in basic metabolic pathways supports the experimental discovery that T. tengcongensis metabolizes sugars as principal energy and carbon source and utilizes thiosulfate and element sulfur, but not sulfate, as electron acceptors. T. tengcongensis, as a gram-negative rod by empirical definitions (such as staining), shares many genes that are characteristics of gram-positive bacteria whereas it is missing molecular components unique to gram-negative bacteria. A strong correlation between the G + C content of tDNA and rDNA genes and the optimal growth temperature is found among the sequenced thermophiles. It is concluded that thermophiles are a biologically and phylogenetically divergent group of prokaryotes that have converged to sustain extreme environmental conditions over evolutionary timescale

INTRODUCTIONThe biotechnological potential and evolutionary significance of thermophiles has led to intensive studies on the biology of anaerobic, saccharolytic thermophiles, which are found in all types of thermal habitats (Brock, 1986 ;Wiegel et al., 1985 ;Kristjansson & Stetter, 1992). Most of these isolates have been characterized and described as members of the genera Thermoanaerobacter, Thermoanaerobacterium and Clostridium (Weigel & Ljungdahl, 1981 ;Lee et al., 1993). Anaerobic thermophiles have been isolated from widely distributed hot springs, for example Thermoanaerobacter brockii (Zeikus et al., 1979) and Thermoanaerobacterium xylanolyticum (Lee et al., 1993) The GenBank accession number for the 16S rRNA gene sequence of strain MB4 T is AF209708.New Zealand (Patel et al., 1985) and Thermoanaerobacter italicus from a thermal spa in Italy (Kozianowski et al., 1997). To date, there are few reports on anaerobic thermophiles from Chinese hot springs. During investigations on the microbial diversity of Chinese hot springs, we isolated a new thermophilic bacterium designated strain MB4 T , which is classified as a new member of the genus Thermoanaerobacter on the basis of phenotypic and phylogenetic analyses. The name Thermoanaerobacter tengcongensis is proposed. METHODSSample source. Mixed sediment and water samples were taken from a hot spring in Tengcong, located in Yunnan Province, China. At the site of sampling, the temperature was 86 mC, the pH value was 7n0 and the NaCl concentration was 0n25 % (w\v).Enrichment, isolation and cultivation. The modified MB medium (Fardeau et al., 1997) used for the experimental studies contained (per litre distilled water) : NH % Cl, 1n0 g;

An alkaline beta-mannanase was purified to homogeneity from a culture broth of alkaliphilic Bacillus sp. N16-5. The enzyme had optimum activity at pH 9.5 and 70 degrees C. It was composed of a single polypeptide chain with a molecular weight of 55 kDa deduced from SDS-PAGE, and its isoelectric point was around pH 4.3. The enzyme efficiently hydrolyzed galactomannan and glucomannan, producing a series of oligosaccharides and monosaccharides. The beta-mannanase gene (manA) contained an open reading frame (ORF) of 1,479 bp, encoding a 32-amino acids signal peptide, and a mature protein of 461 amino acids, with a calculated molecular mass of 50,743 Da. Strain N16-5 ManA, deduced from the manA ORF, exhibited relatively high amino acid similarity to the members of the glycosyl hydrolase family 5. The eight conserved active-site amino acids in family 5 glycosyl hydrolase were found in the deduced amino acid sequence of strain N16-5 ManA.

An intracellular mannanase was identified from the thermoacidophile Alicyclobacillus acidocaldarius Tc-12-31. This enzyme is particularly interesting, because it shows no significant sequence similarity to any known glycoside hydrolase. Gene cloning, biochemical characterization, and structural studies of this novel mannanase are reported in this paper. The gene consists of 963 bp and encodes a 320-amino acid protein, AaManA. Based on its substrate specificity and product profile, AaManA is classified as an endo-␤-1,4-mannanase that is capable of transglycosylation. Kinetic analysis studies revealed that the enzyme required at least five subsites for efficient hydrolysis. The crystal structure at 1.9 Å resolution showed that AaManA adopted a (␤/␣) 8 -barrel fold. Two catalytic residues were identified: Glu 151 at the C terminus of ␤-stand ␤4 and Glu 231 at the C terminus of ␤7. Based on the structure of the enzyme and evidence of its transglycosylation activity, AaManA is placed in clan GH-A. Superpositioning of its structure with that of other clan GH-A enzymes revealed that six of the eight GH-A key residues were functionally conserved in AaManA, with the exceptions being residues Thr 95 and Cys 150 . We propose a model of substrate binding in AaManA in which Glu 282 interacts with the axial OH-C(2) in ؊2 subsites. Based on sequence comparisons, the enzyme was assigned to a new glycoside hydrolase family (GH113) that belongs to clan GH-A.Mannans are polysaccharides found in plants and consist of a backbone of ␤-1,4-linked mannose and glucose units. Mannose residues often carry an ␣-galactosyl substitute at O-6, and the degree of substitution depends on the plant of origin (Fig. 1A) (1). Mannans are widely distributed in nature in parts of the hemicellulose fraction in hardwoods and softwoods (1), legume seeds (2), and beans of carob trees (3).Endo-␤-1,4-mannanases (mannanases; EC 3.2.1.78) are glycoside hydrolases that randomly cleave the ␤-1,4-linkage in mannans (Fig. 1, A and B) (4); these enzymes have been isolated from bacteria, fungi, plants, and some mollusks (5-8). Interest in these enzymes has been increasing due to their importance in hemicellulose hydrolysis and various other applications (5, 9, 10). During the last 2 decades, more than 80 sequences of the catalytic domains of mannanase have been reported (see the CAZy site on the World Wide Web) and classified into glycoside hydrolase (GH) 2 families 5 and 26, based on their sequence similarities (11). In recent years, crystallographic resolution of the structures of these enzymes has yielded information on their structure. At present, the tertiary structures of seven mannanases have been determined, of which five are from GH family 5 (12-16) and two are from family 26 (17, 18). All of these mannanases share a common (␤/␣) 8 barrel fold, a retaining reaction mechanism (Fig. 1C), and two conserved catalytic residues (two glutamate residues at the C termini of ␤4 and ␤7, respectively). Therefore, all of these enzymes have been assigned to the same GH ...