Mitsuaria chitosanitabida gen. nov., sp. nov., an aerobic, chitosanase-producing member of the 'Betaproteobacteria' T , 12 and 13 were found to occupy a separate position in the 'Betaproteobacteria'. Roseateles depolymerans, Rubrivivax gelatinosus and Ideonella dechloratans were their closest neighbours (93-95 % 16S rRNA gene sequence similarity). The 16S rRNA gene sequence and other characteristics suggested that strain 2 belonged to the genus Flavobacterium. DNA-DNA hybridization experiments supported the conclusion that strains 3001 T , 12 and 13 were of the same species (72-78 % DNA hybridization) and only distantly related to I. dechloratans and R. gelatinosus. It is proposed that strains 3001 T
The betaproteobacterium Mitsuaria chitosanitabida (formerly Matsuebacter chitosanotabidus) 3001 produces a chitosanase (ChoA) that is classified in glycosyl hydrolase family 80. While many chitosanase genes have been isolated from various bacteria to date, they show limited homology to the M. chitosanitabida 3001 chitosanase gene (choA). To investigate the phylogenetic distribution of chitosanases analogous to ChoA in nature, we identified 67 chitosan-degrading strains by screening and investigated their physiological and biological characteristics. We then searched for similarities to ChoA by Western blotting and Southern hybridization and selected 11 strains whose chitosanases showed the most similarity to ChoA. PCR amplification and sequencing of the chitosanase genes from these strains revealed high deduced amino acid sequence similarities to ChoA ranging from 77% to 99%. Analysis of the 16S rRNA gene sequences of the 11 selected strains indicated that they are widely distributed in the  and ␥ subclasses of Proteobacteria and the Flavobacterium group. These observations suggest that the ChoA-like chitosanases that belong to family 80 occur widely in a broad variety of bacteria.Chitosan, a linear polymer composed of -1,4-linked glucosamine (GlcN) residues with various numbers of N-acetylated residues, is a deacetylated derivative of chitin. The chitooligosaccharides produced by the enzymatic hydrolysis of chitosan are widely used in the food, agricultural, and pharmaceutical fields because of their various physiological activities.Chitosanases (EC 3.2.1.132) are glycosyl hydrolases that catalyze the hydrolysis of the -1,4-glycosidic linkage of chitosan and thereby produce glucosamine oligosaccharides. To date, many chitosanases have been found in a variety of microorganisms, including bacteria (11, 18, 26, 29, 30, 42, 43, 44, 48), fungi (6, 8, 9, 10, 16, 38, 50), plants (27), and viruses (40). The chitosanases that have been sequenced so far have been classified into four different families in the classification system of glycosyl hydrolases: families 8, 46, 75, and 80 (12, 13, 14). This classification of the chitosanases is based on the amino acid sequence similarity of their catalytic domains. Family 8 includes five chitosanases from bacterial organisms along with cellulase, licheninase, and endo-1,4--xylanase (17,24,45). Family 46 includes 18 chitosanases, 16 from bacterial organisms and 2 from Chlorella viruses (2,3,21,22,33,36,40,46,47). The 3-dimensional structures of the family-46 chitosanases from Streptomyces sp. strain N174 (20) and Bacillus circulans MH-K1 (31) and of the family-8 chitosanase from Bacillus sp. strain K17 (1) have been determined. The catalytic residues of the family-8 and -46 chitosanases are reported to be glutamic acid (Glu) and aspartic acid (Asp) (4). Family 75 includes 17 chitosanases, 14 and 3 of which are from fungi and bacteria, respectively (37, 49).Prior to this study, only two bacterial chitosanases have been classified into family 80 (http://afmb.cnrs-mrs.fr/CAZY/)...
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