Paradoxical conservation of a set of three cellulose-targeting genes in Mycobacterium tuberculosis complex organisms.
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.
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.
Felix
F
Mba Medie
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.
Iskandar
I
Ben Salah
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.
Michel
M
Drancourt
Architecture et Fonction des Macromolécules Biologiques, UMR 6098, IFR 48, CNRS, Université de la Méditerranée et Université de Provence, Marseille, France.
Bernard
B
Henrissat
D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism; D001483:Base Sequence; D002480:Cellulase / Q000235:genetics* / Q000378:metabolism; D002482:Cellulose / Q000378:metabolism*; D017124:Conserved Sequence; D004269:DNA, Bacterial; D005798:Genes, Bacterial; D006801:Humans; D008969:Molecular Sequence Data; D009161:Mycobacterium / Q000201:enzymology / Q000235:genetics*; D009169:Mycobacterium tuberculosis / Q000201:enzymology / Q000235:genetics*; D016133:Polymerase Chain Reaction; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017422:Sequence Analysis, DNA; D014158:Transcription, Genetic
D001426:Bacterial Proteins; D004269:DNA, Bacterial; D002482:Cellulose; D002480:Cellulase