Smith E A, Macfarlane G T
Medical Research Council, Dunn Clinical Nutrition Centre, Cambridge, UK.
J Appl Bacteriol. 1996 Sep;81(3):288-302. doi: 10.1111/j.1365-2672.1996.tb04331.x.
Concentrations of phenolic compounds in human gut contents were more than fourfold higher in the distal colon (6.2 mmol kg-1) compared to the proximal bowel (1.4 mmol kg-1). Tryptophan metabolites were never found in more than trace amounts in large intestinal contents and phenol substituted fatty acids were the major products of aromatic amino acid fermentation that accumulated in the proximal colon, whereas phenol and p-cresol were more important in the distal gut, accounting for 70% of all products of dissimilatory aromatic amino acid metabolism. In vitro incubations of colonic material showed that phenol was produced most rapidly (1.0 mumol g-1 h-1), whereas indole was formed comparatively slowly (0.06 mumol g-1 h-1). Most probable number (MPN) estimations demonstrated that large populations of phenol and indole producing bacteria occur in the large intestine (range log10 9.8-11.5 (g dry wt faeces)-1, mean 10.6, N = 7). With respect to phenolic compounds, phenylacetate and phenylpropionate producers predominated, while indoleacetate-forming bacteria were the major tryptophan-utilizing organisms. Quantitation of products of dissimilatory aromatic amino acid metabolism in MPN tubes showed that phenol and phenylpropionate mainly accumulated at low sample dilutions, whereas phenylacetate, p-cresol, indoleacetate and indolepropionate were formed in greatest amounts at high sample dilutions. The significance of pH and carbohydrate availability with respect to aromatic amino acid metabolism was shown in batch culture fermentation studies, where net production of phenolic compounds by mixed populations of intestinal bacteria was reduced by approximately 33% during growth at pH 5.5 compared to pH 6.8, and by 60% in the presence of a fermentable carbohydrate. Experiments with 16 species of intestinal bacteria belonging to six different genera showed that environmental factors such as low pH and high carbohydrate availability markedly reduced dissimilatory aromatic amino acid metabolism in some organisms, but stimulated this process in others. A three-stage continuous culture model of the colon was used to investigate the effect of system retention time (27.1 or 66.7 h) on aromatic amino acid fermentation. Qualitative and quantitative increases in phenol production occurred from vessel 1 to vessel 3 in this model. Concentrations of phenolic compounds in vessel 3 were three times greater at R = 66.7 h compared to R = 27.1 h. Phenol and p-cresol were not detected in vessel 1, though formation of these metabolites increased from vessel 2 to vessel 3, in a pattern similar to that observed in the distal colon.
人体肠道内容物中酚类化合物的浓度在远端结肠（6.2 mmol·kg-1）比近端肠道（1.4 mmol·kg-1）高出四倍多。色氨酸代谢产物在大肠内容物中从未发现超过痕量，酚取代脂肪酸是近端结肠中积累的芳香族氨基酸发酵的主要产物，而苯酚和对甲酚在远端肠道中更重要，占异化芳香族氨基酸代谢所有产物的70%。结肠材料的体外培养表明，苯酚产生得最快（1.0 μmol·g-1·h-1），而吲哚形成得相对较慢（0.06 μmol·g-1·h-1）。最大可能数（MPN）估计表明，大肠中存在大量产生苯酚和吲哚的细菌（范围为log10 9.8 - 11.5（每克干重粪便）-1，平均值为10.6，N = 7）。关于酚类化合物，产生苯乙酸和苯丙酸的细菌占主导，而形成吲哚乙酸的细菌是主要利用色氨酸的微生物。MPN管中异化芳香族氨基酸代谢产物的定量分析表明，苯酚和苯丙酸主要在低样品稀释度下积累，而苯乙酸、对甲酚、吲哚乙酸和吲哚丙酸在高样品稀释度下形成量最大。分批培养发酵研究表明了pH值和碳水化合物可用性对芳香族氨基酸代谢的重要性，与pH 6.8相比，在pH 5.5生长期间，肠道细菌混合群体产生酚类化合物的净产量降低了约33%，在存在可发酵碳水化合物的情况下降低了60%。对属于六个不同属的16种肠道细菌进行的实验表明，低pH值和高碳水化合物可用性等环境因素在某些生物体中显著降低了异化芳香族氨基酸代谢，但在其他生物体中则刺激了这一过程。使用结肠的三阶段连续培养模型来研究系统保留时间（27.1或66.7小时）对芳香族氨基酸发酵的影响。在该模型中，从容器1到容器3，苯酚产量在定性和定量上都有所增加。与R = 27.1小时相比，在R = 66.7小时时，容器3中酚类化合物的浓度高出三倍。在容器1中未检测到苯酚和对甲酚，尽管这些代谢产物的形成从容器2到容器3有所增加，其模式与在远端结肠中观察到的相似。
