Functional Environmental Screening of a Metagenomic Library Identifies stlA; A Unique Salt Tolerance Locus from the Human Gut Microbiome

Functional environmental screening of metagenomic libraries is a powerful means to identify and assign function to novel genes and their encoded proteins without any prior sequence knowledge. In the current study we describe the identification and subsequent analysis of a salt-tolerant clone from a human gut metagenomic library. Following transposon mutagenesis we identified an unknown gene (stlA, for “salt tolerance locus A”) with no current known homologues in the databases. Subsequent cloning and expression in Escherichia coli MKH13 revealed that stlA confers a salt tolerance phenotype in its surrogate host. Furthermore, a detailed in silico analysis was also conducted to gain additional information on the properties of the encoded StlA protein. The stlA gene is rare when searched against human metagenome datasets such as MetaHit and the Human Microbiome Project and represents a novel and unique salt tolerance determinant which appears to be found exclusively in the human gut environment.

对宏基因组文库（metagenomic libraries）开展功能环境筛选，是无需预先掌握序列信息即可鉴定新基因及其编码蛋白，并为其完成功能注释的高效研究手段。本研究中，我们报道了从人体肠道宏基因组文库中筛选得到一株耐盐克隆，并对其开展后续系统性分析。经转座子诱变（transposon mutagenesis）实验，我们鉴定到一个未知基因stlA（全称为"salt tolerance locus A，耐盐基因座A"），当前数据库中暂无其同源序列。后续将该基因克隆至大肠杆菌（Escherichia coli）MKH13中进行异源表达，结果显示stlA可使其宿主获得耐盐表型。此外，我们还通过计算机预测分析（in silico）开展了详细研究，以获取编码蛋白StlA的相关特性信息。在比对MetaHit与人类微生物组计划（Human Microbiome Project）等人体宏基因组数据集时，stlA基因的检出率极低；该基因代表了一种全新且独特的耐盐决定因子，且似乎仅存在于人体肠道环境中。