THE TERMITE GUT MICROFLORA AS AN OXYGEN SINK - MICROELECTRODE DETERMINATION OF OXYGEN AND PH GRADIENTS IN GUTS OF LOWER AND HIGHER TERMITES
THE TERMITE GUT MICROFLORA AS AN OXYGEN SINK - MICROELECTRODE DETERMINATION OF OXYGEN AND PH GRADIENTS IN GUTS OF LOWER AND HIGHER TERMITES
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DOI：
10.1128/aem.61.7.2681-2687.1995
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发表时间：
1995-07-01
影响因子：
4.4
通讯作者：
BREZNAK, JA
中科院分区：
文献类型：
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作者：
BRUNE, A;EMERSON, D;BREZNAK, JA
尖端直径小于或等于 10 μm 的 Clark 型氧微电极和玻璃 pH 微电极用于获得离体白蚁肠道中氧浓度和 pH 值的高分辨率分布。径向氧分布表明，在低等白蚁 Reticulitermes flavipes (Kollar) 和高等白蚁 Nasutitermes lujae (Wasmann) 中，氧气渗透到上皮表面以下约 150 至 200 μm 的外周后肠内容物中。只有充满微生物、扩大的后肠区室（“胃”）的中心部分（占总体积的不到 40%）完全缺氧，这表明后肠微生物群的某些成员构成了重要的氧汇。根据氧梯度的斜率，我们估计 R. flavipes 和 N. lujae 的整个腹部（肠道组织加上常驻微生物群）分别占完整动物呼吸活动的 21% 和 13%。轴向氧分布也证实，一般来说，只有腹部中心缺氧，而中肠和后肠区域含有大量氧气（空气饱和度分别高达约 50% 和 30%）。一个显着的例外是 N. lujae 后肠的前段（P1 段）的后部，尽管其直径很小（约 250 μm），但完全缺氧。 Nasutitermes nigriceps (Haldeman) 和 Microcerotermes parvus (Haviland) 肠道的轴向 pH 分布表明，当我们从中肠本身（pH 值接近 7）向后移动到后肠的 P1 段（pH >10），然后到达 P3 段（腹腔；pH 值接近 7）时，会出现极端的变化。后者的转变发生在短肠瓣(P2段)和小于500μm的距离内。相比之下，R. flavipes 缺乏易于区分的 P1 片段，不具有明显的碱性区域，并且中肠-后肠连接处周围的 pH 值呈中性。外周后肠腔的含氧状态及其大量的耗氧量，加上先前关于后肠微生物群中存在大量需氧和兼性厌氧细菌的报道，挑战了白蚁后肠是纯粹缺氧环境的观念，并且与高等白蚁中陡峭的轴向 pH 梯度一起，完善了我们对这种微小微生物栖息地的概念。
Clark-type oxygen microelectrodes and glass pH microelectrodes, each with a tip diameter of less than or equal to 10 mu m, were used to obtain high-resolution profiles of oxygen concentrations and pH values in isolated termite guts. Radial oxygen profiles showed that oxygen penetrated into the peripheral hindgut contents up to about 150 to 200 mu m below the epithelial surface in both the lower termite Reticulitermes flavipes (Kollar) and the higher termite Nasutitermes lujae (Wasmann). Only the central portions (comprising less than 40% of the total volume) of the microbe-packed, enlarged hindgut compartments (''paunches'') were completely anoxic, indicating that some members of the hindgut microbiota constitute a significant oxygen sink. From the slopes of the oxygen gradients, we estimated that the entire paunches (gut tissue plus resident microbiota) of R. flavipes and N. lujae accounted for 21 and 13%, respectively, of the respiratory activity of the intact animals. Axial Oxygen profiles also confirmed that in general, only the paunches were anoxic in their centers, whereas midguts and posterior hindgut regions contained significant amounts of oxygen (up to about 50 and 30% air saturation, respectively). A remarkable exception to this was the posterior portion of an anterior segment (the P1 segment) of the hindgut of N. lujae, which was completely anoxic despite its small diameter (approximate to 250 mu m). Axial pH profiles of the guts of Nasutitermes nigriceps (Haldeman) and Microcerotermes parvus (Haviland) revealed that there were extreme shifts as we moved posteriorly from the midgut proper (pH approximate to 7) to the P1 segment of the hindgut (pH >10) and then to the P3 segment (paunch; pH approximate to 7). The latter transition occurred at the short enteric valve (P2 segment) and within a distance of less than 500 mu m. In contrast, R. flavipes, which lacks a readily distinguishable P1 segment, did not possess a markedly alkaline region, and the pH around the midgut-hindgut junction was circumneutral. The oxic status of the peripheral hindgut lumen and its substantial oxygen consumption, together with previous reports of large numbers of aerobic and facultatively anaerobic bacteria in the hindgut microflora, challenge the notion that termite hindguts are a purely anoxic environment and, together with the steep axial pH gradients in higher termites, refine our concept of this tiny microbial habitat.