Architecture et Fonction des Macromolécules Biologiques, UMR 6098, IFR 48, CNRS, Université de la Méditerranée et Université de Provence, Marseille, France.
Unité de Recherche sur les Maladies Infectieuses et Tropicales Emergentes, UMR CNRS 6236, IRD 198, IFR 48, Faculté de Médecine, Université de la Méditerranée, Marseille, France.
Microbiology (Reading). 2010 May;156(Pt 5):1468-1475. doi: 10.1099/mic.0.037812-0. Epub 2010 Feb 11.
The genome of the tuberculosis agent Mycobacterium tuberculosis encodes a putative cellulose-binding protein (CBD2), one candidate cellulase (Cel12), and one fully active cellulase (Cel6). This observation is puzzling, because cellulose is a major component of plant cell walls, whereas M. tuberculosis is a human pathogen without known contact with plants. In order to investigate the biological role of such cellulose-targeting genes in M. tuberculosis we report here the search for and transcription analysis of this set of genes in the genus Mycobacterium. An in silico search for cellulose-targeting orthologues found that only 2.5 % of the sequenced bacterial genomes encode the Cel6, Cel12 and CBD2 gene set simultaneously, including those of the M. tuberculosis complex (MTC) members. PCR amplification and sequencing further demonstrated the presence of these three genes in five non-sequenced MTC bacteria. Among mycobacteria, the combination of Cel6, Cel12 and CBD2 was unique to MTC members, with the exception of Mycobacterium bovis BCG Pasteur, which lacked CBD2. RT-PCR in M. tuberculosis H37Rv indicated that the three cellulose-targeting genes were transcribed into mRNA. The present work shows that MTC organisms are the sole mycobacteria among very few organisms to encode the three cellulose-targeting genes CBD2, Cel6 and Cel12. Our data point toward a unique, yet unknown, relationship with non-plant cellulose-producing hosts such as amoebae.
结核分枝杆菌的基因组编码一个假定的纤维素结合蛋白（CBD2）、一个候选纤维素酶（Cel12）和一个完全活性的纤维素酶（Cel6）。这一观察结果令人费解，因为纤维素是植物细胞壁的主要成分，而结核分枝杆菌是一种人类病原体，与植物没有已知的接触。为了研究这些靶向纤维素的基因在结核分枝杆菌中的生物学作用，我们在这里报告了在分枝杆菌属中搜索和转录分析这组基因的情况。针对纤维素靶向同源物的计算机搜索发现，只有 2.5%的测序细菌基因组同时编码 Cel6、Cel12 和 CBD2 基因簇，包括结核分枝杆菌复合体（MTC）成员的基因组。PCR 扩增和测序进一步证明了这三个基因存在于五种未测序的 MTC 细菌中。在分枝杆菌中，Cel6、Cel12 和 CBD2 的组合仅存在于 MTC 成员中，除了缺乏 CBD2 的牛分枝杆菌卡介苗（Mycobacterium bovis BCG Pasteur）。M. tuberculosis H37Rv 的 RT-PCR 表明，这三个靶向纤维素的基因被转录成 mRNA。本研究表明，MTC 生物是少数编码 CBD2、Cel6 和 Cel12 三个靶向纤维素基因的分枝杆菌之一。我们的数据表明，它们与变形虫等非植物纤维素产生宿主之间存在一种独特但未知的关系。
