Division of Gastroenterology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104.
Division of Gastroenterology, Hepatology, and Nutrition, Children's Hospital of Philadelphia, Philadelphia, PA 19104.
Proc Natl Acad Sci U S A. 2018 Apr 17;115(16):4170-4175. doi: 10.1073/pnas.1718635115. Epub 2018 Apr 2.
The succession from aerobic and facultative anaerobic bacteria to obligate anaerobes in the infant gut along with the differences between the compositions of the mucosally adherent vs. luminal microbiota suggests that the gut microbes consume oxygen, which diffuses into the lumen from the intestinal tissue, maintaining the lumen in a deeply anaerobic state. Remarkably, measurements of luminal oxygen levels show nearly identical pO (partial pressure of oxygen) profiles in conventional and germ-free mice, pointing to the existence of oxygen consumption mechanisms other than microbial respiration. In vitro experiments confirmed that the luminal contents of germ-free mice are able to chemically consume oxygen (e.g., via lipid oxidation reactions), although at rates significantly lower than those observed in the case of conventionally housed mice. For conventional mice, we also show that the taxonomic composition of the gut microbiota adherent to the gut mucosa and in the lumen throughout the length of the gut correlates with oxygen levels. At the same time, an increase in the biomass of the gut microbiota provides an explanation for the reduction of luminal oxygen in the distal vs. proximal gut. These results demonstrate how oxygen from the mammalian host is used by the gut microbiota, while both the microbes and the oxidative chemical reactions regulate luminal oxygen levels, shaping the composition of the microbial community throughout different regions of the gut.
婴儿肠道中需氧菌和兼性厌氧菌向专性厌氧菌的演替，以及黏附于黏膜和腔隙的微生物群落组成的差异表明，肠道微生物会消耗氧气，这些氧气从肠组织扩散到腔隙中，使腔隙保持在深度厌氧状态。值得注意的是，对腔隙氧水平的测量显示，常规和无菌小鼠的 pO（氧分压）曲线几乎完全相同，这表明存在除微生物呼吸以外的氧气消耗机制。体外实验证实，无菌小鼠的腔隙内容物能够通过化学方式消耗氧气（例如，通过脂质氧化反应），尽管其速率明显低于常规饲养小鼠的观察结果。对于常规饲养的小鼠，我们还表明，整个肠道长度中黏附于肠道黏膜和腔隙的肠道微生物群落的分类组成与氧水平相关。同时，肠道微生物群落生物量的增加解释了远端肠道与近端肠道相比腔隙氧气减少的原因。这些结果表明了哺乳动物宿主的氧气如何被肠道微生物群利用，同时微生物和氧化化学反应调节腔隙氧气水平，塑造了整个肠道不同区域的微生物群落组成。
