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The TetR-like transcriptional repressor LfrR controls the expression of the gene encoding the Mycobacterium smegmatis efflux pump LfrA, which actively extrudes fluoroquinolones, cationic dyes, and anthracyclines from the cell and promotes intrinsic antibiotic resistance. The crystal structure of the apoprotein form of the repressor reveals a structurally asymmetric homodimer exhibiting local unfolding and a blocked drug-binding site, emphasizing the significant conformational plasticity of the protein necessary for DNA and multidrug recognition. Crystallographic and calorimetric studies of LfrR-drug complexes further confirm the intrinsic flexibility of the homodimer, which provides a dynamic mechanism to broaden multidrug binding specificity and may be a general property of transcriptional repressors regulating microbial efflux pump expression. doi: 10.1128/JB.00631-09

The cloning and sequencing of a 15437 bp region incorporating the inhA locus from the Mycobacterium avium chromosome was undertaken. The region ws found to contain acnA, fabG, inhA and hemH genes, and invA and invB genes showing homology with p60 invasion protein of Listeria monocytogenes. An RGD motif was contained in six proteins encoded by putative ORFs, with other putative products encoded by ORFs showing little homology with proteins included in the databases.

Nucleotide sequencing of the 75 627 bp segment of the Mycobacterium leprae chromosome with the oriC gene indicated the presence of a gene order that is similar to the replication origin region of prokaryotes. The 75 627 bp segment also contains gyrB, dnaA, dnaB and gidB genes which mediate deoxyribonucleotide metabolism, cell wall synthesis and cell division. Furthermore, the protein products of the open reading frames that are located in the region mediate the generation of serine/threonine protein kinases and protein phosphatase.

The beta-isopropylmalate dehydrogenase gene of Spirulina platensis was cloned by heterologous hybridization. The enzyme is a component of the isopropylpalmitate pathway used by photoautotrophic organisms for leucine synthesis. DNA sequencing and transcriptional analysis done using the dideoxy chain-termination method revealed an open reading frame of 1,065 nucleotides encoding a protein of 355 amino acids with an estimated molecular mass of 39,000 daltons.

Abstract Background Burkholderia cenocepacia is recognized as opportunistic pathogen that can cause lung infections in cystic fibrosis patients. A hallmark of B. cenocepacia infections is the inability to eradicate the organism because of multiple intrinsic antibiotic resistance. As Resistance-Nodulation-Division (RND) efflux systems are responsible for much of the intrinsic multidrug resistance in Gram-negative bacteria, this study aims to identify RND genes in the B. cenocepacia genome and start to investigate their involvement into antimicrobial resistance. Results Genome analysis and homology searches revealed 14 open reading frames encoding putative drug efflux pumps belonging to RND family in B. cenocepacia J2315 strain. By reverse transcription (RT)-PCR analysis, it was found that orf3, orf9, orf11, and orf13 were expressed at detectable levels, while orf10 appeared to be weakly expressed in B. cenocepacia. Futhermore, orf3 was strongly induced by chloramphenicol. The orf2 conferred resistance to fluoroquinolones, tetraphenylphosphonium, streptomycin, and ethidium bromide when cloned and expressed in Escherichia coli KAM3, a strain lacking the multidrug efflux pump AcrAB. The orf2-overexpressing E. coli also accumulate low concentrations of ethidium bromide, which was restored to wild type level in the presence of CCCP, an energy uncoupler altering the energy of the drug efflux pump. Conclusion The 14 RND pumps gene we have identified in the genome of B. cenocepacia suggest that active efflux could be a major mechanism underlying antimicrobial resistance in this microorganism. We have characterized the ORF2 pump, one of these 14 potential RND efflux systems. Its overexpression in E. coli conferred resistance to several antibiotics and to ethidium bromide but it remains to be determined if this pump play a significant role in the antimicrobial intrinsic resistance of B. cenocepacia. The characterization of antibiotic efflux pumps in B. cenocepacia is an obligatory step prior to the design of specific, potent bacterial inhibitors for the improved control of infectious diseases. Consequently, the topic deserves to be further investigated and future studies will involve systematic investigation on the function and expression of each of the RND efflux pump homologs.

Analyzes the gene arrangement and organization in a difference 76 kb fragment encompassing the oriC region of the chromosome of Mycobacterium (M.) leprae. Description of M. leprae; Identification of genes and proteins involved in DNA replication and metabolism; Implications for cell division and genome evolution.

Presents a study which looked at the sequencing and cloning of a 154837 bp region encompassing the inHa locus from the Mycobacterium avium chromosome. Information on the Mycobacterium avium complex; Details on the methodology used to determine the primary structure of the region; Discussion based on the results of the study.

Two mechanisms are thought to be involved in the natural drug resistance of mycobacteria: the mycobacterial cell wall permeability barrier and active multidrug efflux pumps. Genes encoding drug efflux transporters have been isolated from several mycobacterial species. These proteins transport tetracycline, fluoroquinolones, aminoglycosides and other compounds. Recent reports have suggested that efflux pumps may also be involved in transporting isoniazid, one of the main drugs used to treat tuberculosis. This review highlights recent advances in our understanding of efflux-mediated drug resistance in mycobacteria, including the distribution of efflux systems in these organisms, their substrate profiles and their contribution to drug resistance. The balance between the drug transport into the cell and drug efflux is not yet clearly understood, and further studies are required in mycobacteria.

Background: Both intrinsic and acquired multidrug resistance play an important role in the insurgence of tuberculosis. Detailed knowledge of the molecular basis of drug recognition and transport by multidrug transport systems is required for the development of new antibiotics that are not extruded or of inhibitors that block the multidrug transporter and allow traditional antibiotics to be effective., Materials and Methods: We have undertaken the inventory of the drug transporters subfamily, included in the major facilitator superfamily (MFS), encoded by the complete genome of Mycobacterium tuberculosis (MTB). These proteins were identified on the basis of their characteristic stretches of amino acids and transmembrane segments (TMS) number., Conclusions: Genome analysis and searches of homology between the identified transporters and proteins characterized in other organisms revealed 16 open reading frames encoding putative drug efflux pumps belonging to MFS. In the case of two of them, we also have demonstrated that they function as drug efflux proteins.