BACTERIA, like people, can be divided into friend and foe. Inspired by evidence that the friendly sort may help with a range of ailments, many people consume bacteria in the form of yogurts and dietary supplements. Such a smattering of artificial additions, however, represents but a drop in the ocean. There are at least 800 types of bacteria living in the human gut. And research by Steven Gill of the Institute for Genomic Research in Rockville, Maryland, and his colleagues, published in this week's Science, suggests that the collective genome of these organisms is so large that it contains 100 times as many genes as the human genome itself.

　　细菌和人一样也有敌我之分。有益的细菌有助于防治多种疾病已经得到证实，这使得许多人都食用细菌制成的酸奶以及补品。然而，人为地补充这么一点点，只能是杯水车薪。人消化道内生活着至少800种细菌。马里兰州洛克威尔基因组研究中心的史蒂文·吉尔及其同事们在本周《科学》杂志上发表的一篇研究报告认为，这些生物体有着庞大的宏基因组，所包含的基因总数是人类基因组的100倍。

　　Dr Gill and his team were able to come to this conclusion by extracting bacterial DNA from the faeces of two volunteers. Because of the complexity of the samples, they were not able to reconstruct the entire genomes of each of the gut bacteria, just the individual genes. But that allowed them to make an estimate of numbers.

　　吉尔博士和他的研究小组是通过提取两位志愿者粪便中的细菌DNA后得出这一结论的。鉴于标本的复杂性，他们无法重建消化道所有细菌的全部基因组，而只构建了个别基因。但这使得他们能够对基因总数作出估计。