Chitin, a water insoluble β (1,4) linked polymer of N acetyl D glucosamine (GlcNAc), is one of the most abundant renewable forms of biomass. In the natural environment, chitin is decomposed mainly by microorganisms that can utilize it as a nutrient source. Various hydrolases are involved in chitin degradation [i.e., chitinase (EC 3.2.1.14), β N acetylhexosaminidase (EC 3.2.1.52), chitin deacetylase (EC 3.5.1.41) and chitin oligosaccharide deacetylase (COD, EC 3.1.1)]. Chitinivorous microorganisms produce water soluble mono or oligosaccharides from chitin using one or several of these chitinolytic enzymes, and then transport these soluble saccharides into the cell for further degradation. In a previous paper, we reported that Vibrio parahaemolyticus KN1699 produces the heterodisaccharide β N acetyl D glucosaminyl (1,4) D glucosamine (GlcNAc GlcN) as the primary chitin degradation product using following two types of extracellular enzymes: glycoside hydrolase family 18 chitinase, which produces N,N diacetylchitobiose, (GlcNAc)2, from chitin, and carbohydrate esterase (CE) family 4 COD, which hydrolyzes the N acetyl group at the reducing end GlcNAc residue of (GlcNAc)2. Recently, we clarified that GlcNAc GlcN is not only a nutrient for strain KN1699, but also functions as an inducer of chitinase production by this bacterium.4) Moreover, effect of this heterodisaccharide on the chitinase induction was confirmed also in other chitin decomposing Vibrio strains harboring CE family 4 COD genes. These findings suggest that CODs involved in the synthesis of this signal compound are key enzymes for chitin catabolism in some species of Vibrio.To date, aside from COD of strain KN1699, only two CODs, one from Vibrio alginolyticus H 8 5,6) and one from Vibrio cholerae EI Tor N16961, 7) have been purified and characterized. Although these three enzymes have high amino acid sequence homologies (80 99%), their specificities for chitin oligosaccharides are different, indicating the importance of characterizing other microbial CODs. We therefore screened natural sources for bacteria that secrete enzymes that can convert (GlcNAc)2 to GlcNAc GlcN. As a result, we isolated a target bacterium (strain SN184) from the bacteria that adhered on the surface of α chitin flakes (wrapped with tea bag filter paper) sunk in the sea near Tsumekizaki (Shimoda City, Shizuoka Prefecture, Japan). Gram stain results indicated that strain SN 184 is Gram negative. The genotype of strain SN184 was investigated by comparing the nucleotide sequence of its 16S rDNA (GenBank accession no. AB469367) to the sequence database BLASTN. The results confirmed that the isolate is most closely related to many strains of the genus Vibrio (about 97% identity). Although we tried to determine the species of this isolate by investigating its physiological characteristics, it was not possible to determine the species of this bacterium using the methodology outlined in Bergey s Manual of Systematic Bacteriology.
8)The bacterium was therefore named Vibrio sp. SN184.To clone ...
