Tropical Biosphere Research Center, COMB, University of the Ryukyus, Nishihara, Okinawa 903-0213, Japan.
J Insect Physiol. 2012 Jan;58(1):147-54. doi: 10.1016/j.jinsphys.2011.10.012. Epub 2011 Nov 7.
Unlike lower termites, xylophagous higher termites thrive on wood without the aid of symbiotic protists. In the higher termite Nasutitermes takasagoensis, both endogenous endo-β-1,4-glucanase and β-glucosidase genes are expressed in the midgut, which is believed to be the main site of cellulose digestion. To further explore the detailed cellulolytic system in the midgut of N. takasagoensis, we performed immunohistochemistry and digital light microscopy to determine distributions of cellulolytic enzymes in the salivary glands and the midgut as well as the total cellulolytic activity in the midgut. Although cellulolytic enzymes were uniformly produced in the midgut epithelium, the concentration of endo-β-1,4-glucanase activity and luminal volume in the midgut were comparable to those of the wood-feeding lower termite Coptotermes formosanus, which digests cellulose with the aid of hindgut protists. However, the size of ingested wood particles was considerably larger in N. takasagoensis than that in C. formosanus. Nevertheless, it is possible that the cellulolytic system in the midgut of N. takasagoensis hydrolyzes highly crystalline cellulose to a certain extent. The glucose produced did not accumulate in the midgut lumen. Therefore, the present study suggests that the midgut of the higher termite provides the necessary conditions for cellulolysis.
不同于低等白蚁，木食性高等白蚁在没有共生原生生物帮助的情况下也能茁壮成长于木材之上。在高等白蚁 Nasonitermes takasagoensis 中，内源性内切-β-1,4-葡聚糖酶和β-葡萄糖苷酶基因均在中肠中表达，这被认为是纤维素消化的主要部位。为了进一步探索 N. takasagoensis 中肠中详细的纤维素分解系统，我们进行了免疫组织化学和数字光显微镜检查，以确定纤维素分解酶在唾液腺和中肠中的分布以及中肠中的总纤维素分解活性。尽管纤维素分解酶在中肠上皮细胞中均匀产生，但中肠内的内切-β-1,4-葡聚糖酶活性浓度和腔室体积与以肠道原生生物为辅助消化纤维素的木食性低等白蚁 Coptotermes formosanus 相当。然而，在 N. takasagoensis 中，摄入的木屑颗粒大小明显大于 C. formosanus。尽管如此，N. takasagoensis 中肠的纤维素分解系统可能在一定程度上水解高度结晶的纤维素。产生的葡萄糖并没有在中肠腔室中积累。因此，本研究表明，高等白蚁的中肠为纤维素分解提供了必要的条件。
