title: Loss of a conserved 7-methylguanosine modification in 16S rRNA confers low-level streptomycin resistance in bacteria.
abstract: Streptomycin has been an important drug for the treatment of tuberculosis since its discovery in 1944. But numerous strains of Mycobacterium tuberculosis, the bacterial pathogen that causes tuberculosis, are now streptomycin resistant. Although such resistance is often mediated by mutations within rrs, a 16S rRNA gene or rpsL, which encodes the ribosomal protein S12, these mutations are found in a limited proportion of clinically isolated streptomycin-resistant M. tuberculosis strains. Here we have succeeded in identifying a mutation that confers low-level streptomycin resistance to bacteria, including M. tuberculosis. We found that mutations within the gene gidB confer low-level streptomycin resistance and are an important cause of resistance found in 33% of resistant M. tuberculosis isolates. We further clarified that the gidB gene encodes a conserved 7-methylguanosine (m(7)G) methyltransferase specific for the 16S rRNA, apparently at position G527 located in the so-called 530 loop. Thus, we have identified gidB as a new streptomycin-resistance locus and uncovered a resistance mechanism that is mediated by loss of a conserved m(7)G modification in 16S rRNA. The clinical significance of M. tuberculosis gidB mutation also is noteworthy, as gidB mutations emerge spontaneously at a high frequency of 10(-6) and, once emerged, result in vigorous emergence of high-level streptomycin-resistant mutants at a frequency more than 2000 times greater than that seen in wild-type strains. Further studies on the precise function of GidB may provide a basis for developing strategies to suppress pathogenic bacteria, including M. tuberculosis.
authors.affiliation: Microbial Function Laboratory, National Food Research Institute, 2-1-12 Kannondai, Tsukuba, Ibaraki, Japan.
authors.forename: Susumu
authors.initials: S
authors.lastname: Okamoto
authors.forename: Aki
authors.initials: A
authors.lastname: Tamaru
authors.forename: Chie
authors.initials: C
authors.lastname: Nakajima
authors.forename: Kenji
authors.initials: K
authors.lastname: Nishimura
authors.forename: Yukinori
authors.initials: Y
authors.lastname: Tanaka
authors.forename: Shinji
authors.initials: S
authors.lastname: Tokuyama
authors.forename: Yasuhiko
authors.initials: Y
authors.lastname: Suzuki
authors.forename: Kozo
authors.initials: K
authors.lastname: Ochi
mesh_terms: D001483:Base Sequence; D024881:Drug Resistance, Bacterial / Q000235:genetics*; D004926:Escherichia coli / Q000187:drug effects / Q000235:genetics; D029968:Escherichia coli Proteins / Q000235:genetics / Q000378:metabolism; D006151:Guanosine / Q000031:analogs & derivatives* / Q000378:metabolism; D008780:Methyltransferases / Q000235:genetics / Q000378:metabolism; D008826:Microbial Sensitivity Tests; D008969:Molecular Sequence Data; D009154:Mutation; D009169:Mycobacterium tuberculosis / Q000187:drug effects / Q000235:genetics / Q000302:isolation & purification; D012336:RNA, Ribosomal, 16S / Q000378:metabolism*; D000091243:Ribosomal Protein S9; D012269:Ribosomal Proteins / Q000235:genetics; D013307:Streptomycin / Q000494:pharmacology*; D014376:Tuberculosis / Q000382:microbiology
chemical_list: D029968:Escherichia coli Proteins; D012336:RNA, Ribosomal, 16S; D000091243:Ribosomal Protein S9; D012269:Ribosomal Proteins; C000717190:RpsI protein, E coli; C034212:ribosomal protein S12; D006151:Guanosine; C016578:7-methylguanosine; C457299:GidB protein, E coli; D008780:Methyltransferases; D013307:Streptomycin