Identification of a novel family of sequence repeats among prokaryotes

Whole genome comparisons of serotype 4b and 1/2a strains of the food-borne pathogen Listeria monocytogenes reveal new insights into the core genome components of this species

The genomes of three strains of Listeria monocytogenes that have been associated with food-borne illness in the USA were subjected to whole genome comparative analysis. A total of 51, 97 and 69 strain-specific genes were identified in L.monocytogenes strains F2365 (serotype 4b, cheese isolate), F6854 (serotype 1/2a, frankfurter isolate) and H7858 (serotype 4b, meat isolate), respectively. Eighty-three genes were restricted to serotype 1/2a and 51 to serotype 4b strains. These strain- and serotype-specific genes probably contribute to observed differences in pathogenicity, and the ability of the organisms to survive and grow in their respective environmental niches. The serotype 1/2a-specific genes include an operon that encodes the rhamnose biosynthetic pathway that is associated with teichoic acid biosynthesis, as well as operons for five glycosyl transferases and an adenine-specific DNA methyltransferase. A total of 8603 and 105 050 high quality single nucleotide polymorphisms (SNPs) were found on the draft genome sequences of strain H7858 and strain F6854, respectively, when compared with strain F2365. Whole genome comparative analyses revealed that the L.monocytogenes genomes are essentially syntenic, with the majority of genomic differences consisting of phage insertions, transposable elements and SNPs.

An appraisal of the potential for illegitimate recombination in bacterial genomes and its consequences: from duplications to genome reduction

An exhaustive search for shortly spaced repeats in 74 bacterial chromosomes reveals that they are much more numerous than is usually acknowledged. These repeats were divided into five classes: close repeats (CRs), tandem repeats (TRs), simple sequence repeats (SSRs), spaced interspersed direct repeats, and "others." CRs are widespread and constitute the most abundant class, particularly in coding sequences. The other classes are less frequent, but each individual element shows a higher potential for recombination, when the number of repeats and their distances are taken into account. SSRs and TRs are more frequent in pathogens, as expected given their role in contingency loci, but are also widespread in the other bacteria. The analysis of CRs shows that they have an important role in the evolution of genomes, namely by generating duplications and deletions. Several cases compatible with a significant role of small CRs in the formation of large repeats were detected. Also, gene deletion in Buchnera correlates with repeat density, suggesting that CRs may lead to sequence deletion in general and genome reductive evolution of obligatory intracellular bacteria in particular. The assembly of these results indicates that shortly spaced repeats are key players in the dynamics of genome evolution.

Snapshot of moving and expanding clones of Mycobacterium tuberculosis and their global distribution assessed by spoligotyping in an international study

The present update on the global distribution of Mycobacterium tuberculosis complex spoligotypes provides both the octal and binary descriptions of the spoligotypes for M. tuberculosis complex, including Mycobacterium bovis, from >90 countries (13,008 patterns grouped into 813 shared types containing 11,708 isolates and 1,300 orphan patterns). A number of potential indices were developed to summarize the information on the biogeographical specificity of a given shared type, as well as its geographical spreading (matching code and spreading index, respectively). To facilitate the analysis of hundreds of spoligotypes each made up of a binary succession of 43 bits of information, a number of major and minor visual rules were also defined. A total of six major rules (A to F) with the precise description of the extra missing spacers (minor rules) were used to define 36 major clades (or families) of M. tuberculosis. Some major clades identified were the East African-Indian (EAI) clade, the Beijing clade, the Haarlem clade, the Latin American and Mediterranean (LAM) clade, the Central Asian (CAS) clade, a European clade of IS6110 low banders (X; highly prevalent in the United States and United Kingdom), and a widespread yet poorly defined clade (T). When the visual rules defined above were used for an automated labeling of the 813 shared types to define nine superfamilies of strains (Mycobacterium africanum, Beijing, M. bovis, EAI, CAS, T, Haarlem, X, and LAM), 96.9% of the shared types received a label, showing the potential for automated labeling of M. tuberculosis families in well-defined phylogeographical families. Intercontinental matches of shared types among eight continents and subcontinents (Africa, North America, Central America, South America, Europe, the Middle East and Central Asia, and the Far East) are analyzed and discussed.

Improvement of differentiation and interpretability of spoligotyping for Mycobacterium tuberculosis complex isolates by introduction of new spacer oligonucleotides

The direct repeat (DR) region in Mycobacterium tuberculosis complex strains is composed of multiple well-conserved 36-bp DRs interspersed with nonrepetitive DNA spacer sequences of similar size. Clinical isolates show extensive polymorphism in this DR region, and this has led to the development of a 43-spacer reversed line blot methodology: spoligotyping. Although this method has contributed significantly to the molecular epidemiology of tuberculosis in the last decade, the discriminatory power and the readability of this method were not found to be optimal. In order to improve the discriminatory power, the usefulness of 43 redesigned oligonucleotides and the usefulness of 51 new spacer oligonucleotides were evaluated. For 314 M. tuberculosis complex strains isolated in the central part of The Netherlands over a 5-year period, 264 different IS6110 RFLP types could be distinguished, and 160 different spoligotype patterns were identified by traditional spoligotyping. After the introduction of 51 new spacer oligonucleotides, 14 additional spoligotypes were recognized. This enabled us to split 11 clusters of isolates identified by the traditional spoligotyping. Furthermore, on the basis of the new spacer oligonucleotides a dichotomy was found among the Beijing genotype isolates. Among 76 Mycobacterium bovis strains, 20 patterns were found by traditional spoligotyping and 30 patterns were found by novel probe spoligotyping, respectively. Nine M. bovis subsp. caprae isolates yielded six patterns by traditional spoligotyping and eight patterns by novel probe spoligotyping. A part of the redesigned oligonucleotides slightly improved the reading of spoligotype patterns. The reproducibility of spoligotyping, based on internal control probes, invariably yielded a high score; only 4 (1%) of the 314 patient isolates gave discrepant results. Analysis of a set of 31 duplicate M. tuberculosis complex strains demonstrated a 10% error rate for the identification of blinded duplicate samples. In a redundancy analysis, 40 essential spacer oligonucleotides of the 94-spacer sequences were selected, yielding the same number of spoligotype patterns. We propose to leave the traditional commercialized first-generation membrane for spoligotyping unchanged for current applications and to introduce a second-generation spoligotyping membrane whenever extended discrimination is required, e.g., for low-copy-number IS6110 strains or for phylogenetic studies of Beijing genotype strains.