分離高三甲胺產生表型之相關菌種及其功能分析

Abstract

研究顯示因現代人多攝食富含膽鹼及肉鹼的海鮮類以及紅肉，其會被腸道菌叢代謝產生三甲胺（trimethylamine），再被肝臟代謝成氧化三甲胺（trimethylamine-N-oxide），這些代謝產物會促進心血管疾病的發生。我們的合作團隊也發現某些腸道菌與三甲胺的產生具關聯性，以血漿中具有較高濃度氧化三甲胺的受試者的糞便檢體進行宏基因組定序（shotgun metagenomic sequencing），得到得到瘤胃球菌屬Ruminococcus bicirculans、氣味桿菌屬Odoribacter splanchnicus 以及腸桿菌屬Bateroides cellulosilyticus 可能為代謝膽鹼（choline）、肉鹼（carnitine）或g-丁基甜菜鹼（g-butyrobetaine）形成三甲胺的菌種。另外，合作團隊以16S 核醣體DNA進行次世代定序分析較多的受試者糞便檢體後，發現血漿中具有較高濃度氧化三甲胺的部分受試者之糞便檢體含有已證實與三甲胺產生有關之厭氧菌Emergencia timonensis，以及研究Ihubacter massiliensis 。本研究欲分離B. cellulosilyticus 菌株以及I. massiliensis，並測試其是否能代謝膽鹼或肉鹼產生三甲胺。結果顯示可由受試者O27 的糞便中培養出B. cellulosilyticus，命名為B. cellulosilyticus O27 ；I. massiliensis 則尚在分離中。但B. cellulosilyticus O27 似乎不具有代謝膽鹼或肉鹼產生三甲胺的能力。待I. massiliensis 分離出來後，期許能找出其是否具有代謝膽鹼、肉鹼或g-丁基甜菜鹼產生三甲胺的能力，並找出其基因為何。

Recent studies show that dietary choline and L-carnitine, nutrient in seafood and red meat, are converted into trimethylamine (TMA) via gut microbiota-dependent multistep pathway and converted into trimethylamine-N-oxide (TMAO) by hepatic enzyme. The metabolite, TMAO plays an important role in cardiovascular disease (CVD). For example, TMAO accelerates atherosclerosis. Our co-laboratory developed an oral carnitine challenge test (OCCT) to simulate the postprandial plasma TMAO. We cultured the stool samples from healthy volunteers who were accepted OCCT. By shotgun metagenomic sequencing analysis, the data showed that healthy volunteers with high concentrations of TMAO in plasma after OCCT had high proportion of Ruminococcus bicirculans, Odoribacter splanchnicu, and Bateroides cellulosilyticus in their gut microbiota. Moreover, they analyzed healthy OCCT volunteers’ stool samples by bacterial 16S ribosomal DNA sequencing, and found that Emergencia timonensis, which could metabolize g-butyrobetaine to TMA, was significantly enriched in 25.5 % high-TMAO producers. They also found that Ihubacter massiliensis was enriched in 23.5 % high-TMAO producers and both of them were enriched in 5.9 % high-TMAO producers. We want to culture and isolate B. cellulosilyticus and I. massiliensis and investigate whether they could metabolize choline, L-carnitine or g-butyrobetaine to TMA. Our results found that B. cellulosilyticus was not able to metabolize choline, L-carnitine or g-butyrobetaine to TMA. We have yet to culture I. massiliensis. In our conclusion, B. cellulosilyticus was not the gut microbiota which were able to convert choline, L-carnitine or g-butyrobetaine into TMA. I. massiliensis may be the functional bacteria, we have to isolate I. massiliensis and investigate the function of metabolizing choline, L-carnitine or g-butyrobetaine.