Vulevic Jelena, McCartney Anne L, Gee Jennifer M, Johnson Ian T, Gibson Glenn R
Food Microbial Sciences Unit, School of Food Biosciences, The University of Reading, Whiteknights, P.O. Box 226, Reading RG6 6AP, United Kingdom.
Appl Environ Microbiol. 2004 Sep;70(9):5659-66. doi: 10.1128/AEM.70.9.5659-5666.2004.
1,2-sn-Diacylglycerols (DAGs) are activators of protein kinase C (PKC), which is involved in the regulation of colonic mucosal proliferation. Extracellular DAG has been shown to stimulate the growth of cancer cell lines in vitro and may therefore play an important role in tumor promotion. DAG has been detected in human fecal extracts and is thought to be of microbial origin. Hitherto, no attempts have been made to identify the predominant fecal bacterial species involved in its production. We therefore used anaerobic batch culture systems to determine whether fecal bacteria could utilize phosphatidylcholine (0.5% [wt/vol]) to produce DAG. Production was found to be dependent upon the presence of the substrate and was enhanced in the presence of high concentrations of deoxycholate (5 and 10 mM) in the growth medium. Moreover, its production increased with the pH, and large inter- and intraindividual variations were observed between cultures seeded with inocula from different individuals. Clostridia and Escherichia coli multiplied in the fermentation systems, indicating their involvement in phosphatidylcholine metabolism. On the other hand, there was a significant decrease in the number of Bifidobacterium spp. in the presence of phosphatidylcholine. Pure-culture experiments showed that 10 of the 12 strains yielding the highest DAG levels (>50 nmol/ml) were isolated from batch culture enrichments run at pH 8.5. We found that the strains capable of producing large amounts of DAG were predominantly Clostridium bifermentans (8 of 12), followed by Escherichia coli (2 of 12). Interestingly, one DAG-producing strain was Bifidobacterium infantis, which is often considered a beneficial gut microorganism. Our results have provided further evidence that fecal bacteria can produce DAG and that specific bacterial groups are involved in this process. Future strategies to reduce DAG formation in the gut should target these species.
1,2-二酰基-sn-甘油（DAGs）是蛋白激酶C（PKC）的激活剂，PKC参与结肠黏膜增殖的调节。细胞外DAG已被证明在体外可刺激癌细胞系的生长，因此可能在肿瘤促进中起重要作用。DAG已在人类粪便提取物中检测到，并且被认为源自微生物。迄今为止，尚未尝试鉴定参与其产生的主要粪便细菌种类。因此，我们使用厌氧分批培养系统来确定粪便细菌是否可以利用磷脂酰胆碱（0.5%[重量/体积]）产生DAG。发现产量取决于底物的存在，并且在生长培养基中存在高浓度的脱氧胆酸盐（5和10 mM）时产量会增加。此外，其产量随pH值增加，并且在用来自不同个体的接种物接种的培养物之间观察到个体间和个体内的巨大差异。梭菌属和大肠杆菌在发酵系统中繁殖，表明它们参与磷脂酰胆碱代谢。另一方面，在存在磷脂酰胆碱的情况下双歧杆菌属的数量显著减少。纯培养实验表明，产生最高DAG水平（>50 nmol/ml）的12个菌株中有10个是从pH 8.5的分批培养富集物中分离出来的。我们发现能够产生大量DAG的菌株主要是双发酵梭菌（12个中的8个），其次是大肠杆菌（12个中的2个）。有趣的是，一个产生DAG的菌株是婴儿双歧杆菌，它通常被认为是有益的肠道微生物。我们的结果提供了进一步的证据，表明粪便细菌可以产生DAG，并且特定的细菌群体参与了这一过程。未来减少肠道中DAG形成的策略应针对这些物种。
