2006 年 20 巻 2 号 p. 49-54
Larvae of the Japanese horned beetle, Trypoxylus dichotomus septentrionalis (Kono 1931), feed on putrid wood and leaf litter, and are assumed to play important roles in the degradation of polysaccharides produced by broadleaf trees in Japan. Wada et al. showed the presence of strong degrading activities against several polysaccharides, e.g., β-1, 4-xylan, pectin, and β-1,3-glucan, in the contents of the larval gut and an alkaline pH (pH 10) of the contents of the larval midgut. Xylanolytic strains of bacteria, H05TDL, F09TDL, and W02TDL, were isolated, by use of alkaline media containing 0.5% xylan, from the hindgut and feces of T. dichotomus larvae and putrid wood used for feeding of the larva; and these strains seemed to belong to the genus Dietzia by 16S rDNA analysis. The strain H05TDL showed higher xylanolytic activity at alkaline pH than at neutral pH. The cells of this strain were Gram-positive aerobic rods containing short-chain mycolic acids (33–40 carbon atoms) and arabinose and galactose as the major cell-wall sugars, which also support that the strain belongs to the genus Dietzia. The bacterium grew well between pH 6.8 and 9.6 (optimally at pH 8.3), and produced β-1,4-xylanase, which showed its maximum activity at pH 9.4. In the pH range between 8 and 10, the enzyme activity was 70% of the maximum activity or higher, suggesting that the β-1,4-xylanase may have become adapted to the alkaline lumen of the gut.
