Leprosy, a chronic human neurological disease, results from infection with the obligate intracellular pathogen Mycobacterium leprae, a close relative of the tubercle bacillus. Mycobacterium leprae has the longest doubling time of all known bacteria and has thwarted every effort at culture in the laboratory. Comparing the 3.27-megabase (Mb) genome sequence of an armadillo-derived Indian isolate of the leprosy bacillus with that of Mycobacterium tuberculosis (4.41 Mb) provides clear explanations for these properties and reveals an extreme case of reductive evolution. Less than half of the genome contains functional genes but pseudogenes, with intact counterparts in M. tuberculosis, abound. Genome downsizing and the current mosaic arrangement appear to have resulted from extensive recombination events between dispersed repetitive sequences. Gene deletion and decay have eliminated many important metabolic activities including siderophore production, part of the oxidative and most of the microaerophilic and anaerobic respiratory chains, and numerous catabolic systems and their regulatory circuits.

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To understand the evolution, attenuation, and variable protective efficacy of bacillus Calmette-Gué rin (BCG) vaccines, Mycobacterium bovis BCG Pasteur 1173P2 has been subjected to comparative genome and transcriptome analysis. The 4,374,522-bp genome contains 3,954 protein-coding genes, 58 of which are present in two copies as a result of two independent tandem duplications, DU1 and DU2. DU1 is restricted to BCG Pasteur, although four forms of DU2 exist; DU2-I is confined to early BCG vaccines, like BCG Japan, whereas DU2-III and DU2-IV occur in the late vaccines. The glycerol-3-phosphate dehydrogenase gene, glpD2, is one of only three genes common to all four DU2 variants, implying that BCG requires higher levels of this enzyme to grow on glycerol. Further amplification of the DU2 region is ongoing, even within vaccine preparations used to immunize humans. An evolutionary scheme for BCG vaccines was established by analyzing DU2 and other markers. Lesions in genes encoding -factors and pleiotropic transcriptional regulators, like PhoR and Crp, were also uncovered in various BCG strains; together with gene amplification, these affect gene expression levels, immunogenicity, and, possibly, protection against tuberculosis. Furthermore, the combined findings suggest that early BCG vaccines may even be superior to the later ones that are more widely used.glycerol metabolism ͉ live vaccines ͉ tandem duplications ͉ tuberculosis

Leprosy, a chronic human disease with potentially debilitating neurological consequences, results from infection with Mycobacterium leprae. This unculturable pathogen has undergone extensive reductive evolution, with half of its genome now occupied by pseudogenes. Using comparative genomics, we demonstrated that all extant cases of leprosy are attributable to a single clone whose dissemination worldwide can be retraced from analysis of very rare single-nucleotide polymorphisms. The disease seems to have originated in Eastern Africa or the Near East and spread with successive human migrations. Europeans or North Africans introduced leprosy into West Africa and the Americas within the past 500 years.

In several Gram-positive and Gram-negative bacteria glutamate decarboxylases play an important role in the maintenance of cellular homeostasis in acid environments. Here, new insight is brought to the regulation of the acid response in Escherichia coli. Overexpression of yhiE, similarly to overexpression of gadX, a known regulator of glutamate decarboxylase expression, leads to increased resistance of E. coli strains under high acid conditions, suggesting that YhiE is a regulator of gene expression in the acid response. Target genes of both YhiE (renamed GadE) and GadX were identified by a transcriptomic approach. In vitro experiments with GadE purified protein provided evidence that this regulator binds to the promoter region of these target genes. Several of them are clustered together on the chromosome and this chromosomal organization is conserved in many E. coli strains. Detailed structural (in silico) analysis of this chromosomal region suggests that the promoters of the corresponding genes are preferentially denatured. These results, along with the G+C signature of the chromosomal region, support the existence of a fitness island for acid adaptation on the E. coli chromosome.

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During invasion, apicomplexan parasites form an intimate circumferential contact with the host cell, the tight junction (TJ), through which they actively glide. The TJ, which links the parasite motor to the host cell cytoskeleton, is thought to be composed of interacting apical membrane antigen 1 (AMA1) and rhoptry neck (RON) proteins. Here we find that, in Plasmodium berghei, while both AMA1 and RON4 are important for merozoite invasion of erythrocytes, only RON4 is required for sporozoite invasion of hepatocytes, indicating that RON4 acts independently of AMA1 in the sporozoite. Further, in the Toxoplasma gondii tachyzoite, AMA1 is dispensable for normal RON4 ring and functional TJ assembly but enhances tachyzoite apposition to the cell and internalization frequency. We propose that while the RON proteins act at the TJ, AMA1 mainly functions on the zoite surface to permit correct attachment to the cell, which may facilitate invasion depending on the zoite-cell combination.

Myotonic dystrophy (DM) is caused by a CTG repeat expansion in the 3'UTR of the DM protein kinase (DMPK) gene. A very high level of instability is observed through successive generations and the size of the repeat is generally correlated with the severity of the disease and with age at onset. Furthermore, tissues from DM patients exhibit somatic mosaicism that increases with age. We generated transgenic mice carrying large human genomic sequences with 20, 55 or >300 CTG, cloned from patients from the same affected DM family. Using large human flanking sequences and a large amplification, we demonstrate that the intergenerational CTG repeat instability is reproduced in mice, with a strong bias towards expansions and with the same sex- and size-dependent characteristics as in humans. Moreover, a high level of instability, increasing with age, can be observed in tissues and in sperm. Although we did not observe dramatic expansions (or 'big jumps' over several hundred CTG repeats) as in congenital forms of DM, our model carrying >300 CTG is the first to show instability so close to the human DM situation. Our three models carrying different sizes of CTG repeat provide insight on the different factors modulating the CTG repeat instability.