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首页> 美国卫生研究院文献>Applied and Environmental Microbiology >Hydrogen Concentration Profiles at the Oxic-Anoxic Interface: a Microsensor Study of the Hindgut of the Wood-Feeding Lower Termite Reticulitermes flavipes (Kollar)
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Hydrogen Concentration Profiles at the Oxic-Anoxic Interface: a Microsensor Study of the Hindgut of the Wood-Feeding Lower Termite Reticulitermes flavipes (Kollar)

机译：氧-缺氧界面处的氢浓度曲线：木材喂食的白蚁网状黄素（Kollar）的后肠的微传感器研究

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Molecular hydrogen is a key intermediate in lignocellulose degradation by the microbial community of termite hindguts. With polarographic, Clark-type H(inf2) microelectrodes, we determined H(inf2) concentrations at microscale resolution in the gut of the wood-feeding lower termite Reticulitermes flavipes (Kollar). Axial H(inf2) concentration profiles obtained from isolated intestinal tracts embedded in agarose Ringer solution clearly identified the voluminous hindgut paunch as the site of H(inf2) production. The latter was strictly coupled with both a low redox potential (E(infh) = -200 mV) and the absence of oxygen, in agreement with the growth requirements of the cellulolytic, H(inf2)-producing flagellates located in the hindgut paunch. Luminal H(inf2) partial pressures were much higher than expected (ca. 5 kPa) and increased more than threefold when the guts were incubated under a N(inf2) headspace. Radial H(inf2) concentration gradients showed a steep decrease from the gut center towards the periphery, indicating the presence of H(inf2)-consuming activities both within the lumen and at the gut epithelium. Measurements under controlled gas headspace showed that the gut wall was also a sink for externally supplied H(inf2), both under oxic and anoxic conditions. With O(inf2) microelectrodes, we confirmed that the H(inf2) sink below the gut epithelium is located within the microoxic gut periphery, but the H(inf2)-consuming activity itself, at least a substantial part of it, was clearly due to an anaerobic process. These results are in accordance with the recently reported presence of methanogens attached in large numbers to the luminal side of the hindgut epithelium of R. flavipes. If the oxygen partial pressure was increased, O(inf2) penetrated deeper and H(inf2) production was suppressed; it ceased completely as soon as the gut was fully oxic. In experiments with living termites, externally supplied H(inf2) (20 kPa) stimulated methane formation five- to sixfold to 0.93 (mu)mol (g of termite)(sup-1) h(sup-1), indicating that the methanogenic activity in R. flavipes hindguts is not saturated for hydrogen under in situ conditions. This rate was in good agreement with the H(inf2) uptake rates exhibited by isolated hindguts, which would account for more than half of the CH(inf4) formed by living termites under comparable conditions.
机译：分子氢是白蚁后肠的微生物群落在木质纤维素降解中的关键中间体。极谱法，克拉克型H（inf2）微电极，我们在以木材为食的下白蚁网纹黄酮（Kollar）的肠道中以微尺度分辨率确定了H（inf2）浓度。从琼脂糖林格溶液中嵌入的独立肠道中获得的轴向H（inf2）浓度曲线清楚地确定了大量的后肠pa痛是H（inf2）产生的部位。后者与低氧化还原电势（E（infh）= -200 mV）和没有氧气严格结合，与位于后肠pa中的纤维素分解产生H（inf2）的鞭毛的生长要求相一致。当在N（inf2）顶空下孵育肠道时，发光的H（inf2）分压比预期的要高得多（约5 kPa），并且增加了三倍多。径向H（inf2）浓度梯度显示从肠道中心向外围急剧下降，表明管腔内和肠道上皮均存在消耗H（inf2）的活动。在可控气体顶空下的测量表明，在有氧和无氧条件下，肠壁也是外部供应的H（inf2）的汇。使用O（inf2）微电极，我们证实了肠道上皮下的H（inf2）汇位于微氧肠道周围，但是很明显，消耗H（inf2）本身的活动（至少是其中的很大一部分）厌氧过程。这些结果与最近报道的产甲烷黄菌大量附着在黄萎病菌后肠上皮腔侧的结果一致。如果增加氧分压，则O（inf2）的渗透会更深，H（inf2）的生成会受到抑制；一旦肠道完全有氧，它就会完全停止。在活白蚁的实验中，外部供应的H（inf2）（20 kPa）刺激了甲烷形成五至六倍，达到0.93（μ）mol（g白蚁）（sup-1）h（sup-1），表明产甲烷在原位条件下，R。flavipes后肠中的活性对于氢而言并不饱和。该速率与孤立的后肠表现出的H（inf2）摄取率非常吻合，后者在相当的条件下占活白蚁形成的CH（inf4）的一半以上。

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