最新《Nature》奇妙的基因礼物

　　

生物通报道，法国Université Pierre和加拿大University of Victoria的科学家近期发现了一个有趣的现象，人类肠道的微生物基因交流有助人类提高对食物消化能力，相关成果文章Transfer of carbohydrate-active enzymes from marine bacteria to Japanese gut microbiota公布在最新一期的Nature上。 

 

肠道微生物群落所起的有用作用之一是，提供人类基因组中所缺的消化酶。例如，来自在整个演化过程中一直是人类饮食构成部分的陆地植物的多糖，就是在肠道中被碳水化合物活性酶（CAZymes）分解的，它们当中很多都是来自类杆菌的具有高度特异性的酶。

 

然而，人们对帮助消化可食性海藻如紫菜、海白菜和裙带菜（常见于日本菜）的肠道酶却知之甚少。现在，能够消化来自紫菜类红海藻的硫酸多糖的碳水化合物活性酶已在海洋类杆菌分离菌种中被发现。

 

法国化学家Mirjam Czjzek一项新的研究发现，日本人的肠道细菌中存在一种能帮助消化海藻的酶，而其它地区的居民身上缺乏此种酶。出乎意料的是，基因组数据挖掘显示，这种酶存在于日本人的肠道细菌中，但在美国人的肠道细菌中却没有。

 

法国化学家Mirjam Czjzek最初没想去对比跨文化的饮食习惯，而是研究如何消化海藻片。由碳水化合物组成的海藻有成串的硫分子，需要特殊的酶才能分解。为了找出究竟需要哪一种酶，研究人员测序了一种以海藻为食的海洋细菌，他们发现了5个可能属于分解海藻的酶的基因。他们随后将五个基因转移到另一种细菌身上，强迫它去吞食海藻碳水化合物，观察到有两个基因最为活跃。Czjzek怀疑这些基因可能躲藏在某处，因此她使用名为BLAST的计算方法扫描基因数据库，结果发生了出乎意料的事。她发现一个人体肠道样本中的一种海洋细菌含有这些基因。这种细菌只存在于日本人中间。

 

这表明，最近（这里说的“最近”是从演化意义上来讲的）发生了从一种来自海洋环境的类杆菌向日本人肠道细菌“Bacteroides plebeius”的基因转移。紫菜传统上用于寿司中，这表明，接触未灭菌的食物，在带有不同碳水化合物活性酶的肠道细菌在体内积累中是一个普遍因素。日本人可能是通过食用了含有一种特殊细菌的海藻而首次获得这种酶的。

（生物通 小茜）

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生物通推荐原文检索

Transfer of carbohydrate-active enzymes from marine bacteria to Japanese gut microbiota

Jan-Hendrik Hehemann1,2,3, Gaëlle Correc1,2, Tristan Barbeyron1,2, William Helbert1,2, Mirjam Czjzek1,2 & Gurvan Michel1,2

 

Université Pierre et Marie Curie, Paris 6,

Centre National de la Recherche Scientifique, Végétaux marins et Biomolécules UMR 7139, Station Biologique de Roscoff, Roscoff F 29682, France

Present address: Biochemistry and Microbiology, University of Victoria, PO Box 3055 STN CSC, Victoria, British Columbia V8W 3PG, Canada.

Correspondence to: Mirjam Czjzek1,2Gurvan Michel1,2 Correspondence and requests for materials should be addressed to M.C. (Email: [e-mail]) or G.M. (Email: [e-mail]).

 

【Abstract】

Gut microbes supply the human body with energy from dietary polysaccharides through carbohydrate active enzymes, or CAZymes1, which are absent in the human genome. These enzymes target polysaccharides from terrestrial plants that dominated diet throughout human evolution2. The array of CAZymes in gut microbes is highly diverse, exemplified by the human gut symbiont Bacteroides thetaiotaomicron 3, which contains 261 glycoside hydrolases and polysaccharide lyases, as well as 208 homologues of susC and susD-genes coding for two outer membrane proteins involved in starch utilization1, 4. A fundamental question that, to our knowledge, has yet to be addressed is how this diversity evolved by acquiring new genes from microbes living outside the gut. Here we characterize the first porphyranases from a member of the marine Bacteroidetes, Zobellia galactanivorans, active on the sulphated polysaccharide porphyran from marine red algae of the genus Porphyra. Furthermore, we show that genes coding for these porphyranases, agarases and associated proteins have been transferred to the gut bacterium Bacteroides plebeius isolated from Japanese individuals5. Our comparative gut metagenome analyses show that porphyranases and agarases are frequent in the Japanese population6 and that they are absent in metagenome data7 from North American individuals. Seaweeds make an important contribution to the daily diet in Japan (14.2 g per person per day)8, and Porphyra spp. (nori) is the most important nutritional seaweed, traditionally used to prepare sushi9, 10. This indicates that seaweeds with associated marine bacteria may have been the route by which these novel CAZymes were acquired in human gut bacteria, and that contact with non-sterile food may be a general factor in CAZyme diversity in human gut microbes.