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1.  Recognition of Potentially Novel Human Disease-Associated Pathogens by Implementation of Systematic 16S rRNA Gene Sequencing in the Diagnostic Laboratory▿ †  
Journal of Clinical Microbiology  2010;48(9):3397-3402.
Clinical isolates that are difficult to identify by conventional means form a valuable source of novel human pathogens. We report on a 5-year study based on systematic 16S rRNA gene sequence analysis. We found 60 previously unknown 16S rRNA sequences corresponding to potentially novel bacterial taxa. For 30 of 60 isolates, clinical relevance was evaluated; 18 of the 30 isolates analyzed were considered to be associated with human disease.
PMCID: PMC2937732  PMID: 20631113
2.  The Uracil DNA Glycosylase UdgB of Mycobacterium smegmatis Protects the Organism from the Mutagenic Effects of Cytosine and Adenine Deamination▿  
Journal of Bacteriology  2009;191(20):6312-6319.
Spontaneous hydrolytic deamination of DNA bases represents a considerable mutagenic threat to all organisms, particularly those living in extreme habitats. Cytosine is readily deaminated to uracil, which base pairs with adenine during replication, and most organisms encode at least one uracil DNA glycosylase (UDG) that removes this aberrant base from DNA with high efficiency. Adenine deaminates to hypoxanthine approximately 10-fold less efficiently, and its removal from DNA in vivo has to date been reported to be mediated solely by alkyladenine DNA glycosylase. We previously showed that UdgB from Pyrobaculum aerophilum, a hyperthermophilic crenarchaeon, can excise hypoxanthine from oligonucleotide substrates, but as this organism is not amenable to genetic manipulation, we were unable to ascertain that the enzyme also has this role in vivo. In the present study, we show that UdgB from Mycobacterium smegmatis protects this organism against mutagenesis associated with deamination of both cytosine and adenine. Together with Ung-type uracil glycosylase, M. smegmatis UdgB also helps attenuate the cytotoxicity of the antimicrobial agent 5-fluorouracil.
PMCID: PMC2753029  PMID: 19684133
3.  Characterization of the Mycobacterial NER System Reveals Novel Functions of the uvrD1 Helicase▿  
Journal of Bacteriology  2008;191(2):555-562.
In this study, we investigated the role of the nucleotide excision repair (NER) pathway in mycobacterial DNA repair. Mycobacterium smegmatis lacking the NER excinuclease component uvrB or the helicase uvrD1 gene and a double knockout lacking both genes were constructed, and their sensitivities to a series of DNA-damaging agents were analyzed. As anticipated, the mycobacterial NER system was shown to be involved in the processing of bulky DNA adducts and interstrand cross-links. In addition, it could be shown to exert a protective effect against oxidizing and nitrosating agents. Interestingly, inactivation of uvrB and uvrD1 significantly increased marker integration frequencies in gene conversion assays. This implies that in mycobacteria (which lack the postreplicative mismatch repair system) NER, and particularly the UvrD1 helicase, is involved in the processing of a subset of recombination-associated mismatches.
PMCID: PMC2620815  PMID: 19011038
4.  Stabilization of the genome of the mismatch repair deficient Mycobacterium tuberculosis by context-dependent codon choice 
BMC Genomics  2008;9:249.
The rate at which a stretch of DNA mutates is determined by the cellular systems for DNA replication and repair, and by the nucleotide sequence of the stretch itself. One sequence feature with a particularly strong influence on the mutation rate are nucleotide repeats. Some microbial pathogens use nucleotide repeats in their genome to stochastically vary phenotypic traits and thereby evade host defense. However, such unstable sequences also come at a cost, as mutations are often deleterious. Here, we analyzed how these opposing forces shaped genome stability in the human pathogen Mycobacterium tuberculosis. M. tuberculosis lacks a mismatch repair system, and this renders nucleotide repeats particularly unstable.
We found that proteins of M. tuberculosis are encoded by using codons in a context-dependent manner that prevents the emergence of nucleotide repeats. This context-dependent codon choice leads to a strong decrease in the estimated frame-shift mutation rate and thus to an increase in genome stability.
These results indicate that a context-specific codon choice can partially compensate for the lack of a mismatch repair system, and helps to maintain genome integrity in this pathogen.
PMCID: PMC2430213  PMID: 18507851
5.  A Mycobacterial smc Null Mutant Is Proficient in DNA Repair and Long-Term Survival▿  
Journal of Bacteriology  2007;190(1):452-456.
SMC (structural maintenance of chromosomes) proteins play fundamental roles in various aspects of chromosome organization and dynamics, including repair of DNA damage. Mutant strains of Mycobacterium smegmatis and Mycobacterium tuberculosis defective in SMC were constructed. Surprisingly, inactivation of smc did not result in recognizable phenotypes in hallmark assays characteristic for the function of these genes. This is in contrast to data for smc null mutants in other species.
PMCID: PMC2223740  PMID: 17981972

Results 1-5 (5)