Macrotene chromosomes provide insights to a new mechanism of high-order gene amplification in eukaryotes.

Copy number variation of chromosomal segments is now recognized as a major source of genetic polymorphism within natural populations of eukaryotes, as well as a possible cause of genetic diseases in humans, including cancer, but its molecular bases remain incompletely understood. In the baker's yeast Saccharomyces cerevisiae, a variety of low-order amplifications (segmental duplications) were observed after adaptation to limiting environmental conditions or recovery from gene dosage imbalance, and interpreted in terms of replication-based mechanisms associated or not with homologous recombination. Here we show the emergence of novel high-order amplification structures, with corresponding overexpression of embedded genes, during evolution under favourable growth conditions of severely unfit yeast cells bearing genetically disabled genomes. Such events form massively extended chromosomes, which we propose to call macrotene, whose characteristics suggest the products of intrachromosomal rolling-circle type of replication structures, probably initiated by increased accidental template switches under important cellular stress conditions.

Comparison of widely used Listeria monocytogenes strains EGD, 10403S, and EGD-e highlights genomic variations underlying differences in pathogenicity.

For nearly 3 decades, listeriologists and immunologists have used mainly three strains of the same serovar (1/2a) to analyze the virulence of the bacterial pathogen Listeria monocytogenes. The genomes of two of these strains, EGD-e and 10403S, were released in 2001 and 2008, respectively. Here we report the genome sequence of the third reference strain, EGD, and extensive genomic and phenotypic comparisons of the three strains. Strikingly, EGD-e is genetically highly distinct from EGD (29,016 single nucleotide polymorphisms [SNPs]) and 10403S (30,296 SNPs), and is more related to serovar 1/2c than 1/2a strains. We also found that while EGD and 10403S strains are genetically very close (317 SNPs), EGD has a point mutation in the transcriptional regulator PrfA (PrfA*), leading to constitutive expression of several major virulence genes. We generated an EGD-e PrfA* mutant and showed that EGD behaves like this strain in vitro, with slower growth in broth and higher invasiveness in human cells than those of EGD-e and 10403S. In contrast, bacterial counts in blood, liver, and spleen during infection in mice revealed that EGD and 10403S are less virulent than EGD-e, which is itself less virulent than EGD-e PrfA*. Thus, constitutive expression of PrfA-regulated virulence genes does not appear to provide a significant advantage to the EGD strain during infection in vivo, highlighting the fact that in vitro invasion assays are not sufficient for evaluating the pathogenic potential of L. monocytogenes strains. Together, our results pave the way for deciphering unexplained differences or discrepancies in experiments using different L. monocytogenes strains. IMPORTANCE Over the past 3 decades, Listeria has become a model organism for host-pathogen interactions, leading to critical discoveries in a broad range of fields, including bacterial gene regulation, cell biology, and bacterial pathophysiology. Scientists studying Listeria use primarily three pathogenic strains: EGD, EGD-e, and 10403S. Despite many studies on EGD, it is the only one of the three strains whose genome has not been sequenced. Here we report the sequence of its genome and a series of important genomic and phenotypic differences between the three strains, in particular, a critical mutation in EGD's PrfA, the main regulator of Listeria virulence. Our results show that the three strains display differences which may play an important role in the virulence differences observed between the strains. Our findings will be of critical relevance to listeriologists and immunologists who have used or may use Listeria as a tool to study the pathophysiology of listeriosis and immune responses.

Comparative genomics of emerging pathogens in the Candida glabrata clade.

BACKGROUND: Candida glabrata follows C. albicans as the second or third most prevalent cause of candidemia worldwide. These two pathogenic yeasts are distantly related, C. glabrata being part of the Nakaseomyces, a group more closely related to Saccharomyces cerevisiae. Although C. glabrata was thought to be the only pathogenic Nakaseomyces, two new pathogens have recently been described within this group: C. nivariensis and C. bracarensis. To gain insight into the genomic changes underlying the emergence of virulence, we sequenced the genomes of these two, and three other non-pathogenic Nakaseomyces, and compared them to other sequenced yeasts. RESULTS: Our results indicate that the two new pathogens are more closely related to the non-pathogenic N. delphensis than to C. glabrata. We uncover duplications and accelerated evolution that specifically affected genes in the lineage preceding the group containing N. delphensis and the three pathogens, which may provide clues to the higher propensity of this group to infect humans. Finally, the number of Epa-like adhesins is specifically enriched in the pathogens, particularly in C. glabrata. CONCLUSIONS: Remarkably, some features thought to be the result of adaptation of C. glabrata to a pathogenic lifestyle, are present throughout the Nakaseomyces, indicating these are rather ancient adaptations to other environments. Phylogeny suggests that human pathogenesis evolved several times, independently within the clade. The expansion of the EPA gene family in pathogens establishes an evolutionary link between adhesion and virulence phenotypes. Our analyses thus shed light onto the relationships between virulence and the recent genomic changes that occurred within the Nakaseomyces. SEQUENCE ACCESSION NUMBERS: Nakaseomyces delphensis: CAPT01000001 to CAPT01000179Candida bracarensis: CAPU01000001 to CAPU01000251Candida nivariensis: CAPV01000001 to CAPV01000123Candida castellii: CAPW01000001 to CAPW01000101Nakaseomyces bacillisporus: CAPX01000001 to CAPX01000186.

Draft Genome Sequences of Five Strains of Lactobacillus acidophilus, Strain CIP 76.13T, Isolated from Humans, Strains CIRM-BIA 442 and CIRM-BIA 445, Isolated from Dairy Products, and Strains DSM 20242 and DSM 9126 of Unknown Origin.

Lactobacillus acidophilus is a natural inhabitant of mammalian gastrointestinal systems and is used in dairy and pharmaceutical products. Five draft genome sequences, covering 1,995,790 nucleotides (nt) on average, are divided into 19 to 34 scaffolds covering 1,995 to 2,053 genes. The draft genome sequences were compared to the sequence of the L. acidophilus NCFM dairy strain.

Draft Genome Sequence of Lactobacillus pasteurii CRBIP 24.76T.

We report the draft genome sequence of the type strain Lactobacillus pasteurii CRBIP 24.76, which is closely related to L. gigeriorum CRBIP 24.85(T), isolated from a chicken crop. The total length of the 29 contigs is about 1.9 Mb, with a G+C content of 40% and 1,946 coding sequences.

Draft Genome Sequence of Lactobacillus hominis Strain CRBIP 24.179T, Isolated from Human Intestine.

We report the draft genome sequence of the strain Lactobacillus hominis CRBIP 24.179(T), isolated from a human clinical sample. The total length of the 28 contigs is about 1.9 Mb, with a G+C content of 37% and 1,983 coding sequences.

Draft Genome Sequences of Lactobacillus equicursoris CIP 110162T and Lactobacillus sp. Strain CRBIP 24.137, Isolated from Thoroughbred Racehorse Feces and Human Urine, Respectively.

We report the draft genome sequences of strain Lactobacillus equicursoris CIP 110162(T), isolated from racehorse breed feces, and Lactobacillus sp. strain CRBIP 24.137, isolated from human urine; the two strains are closely related. The total lengths of the 116 and 62 scaffolds are about 2.157 and 2.358 Mb, with G+C contents of 46 and 45% and 2,279 and 2,342 coding sequences (CDSs), respectively.

Draft genome sequence of Lactobacillus gigeriorum CRBIP 24.85T, isolated from a chicken crop.

We report the draft genome of the strain Lactobacillus gigeriorum CRBIP 24.85(T), isolated from a chicken crop. The total length of the 60 scaffolds is about 1.9 Mb, with a GC content of 38% and 2,062 protein-coding sequences (CDS).

From array-based hybridization of Helicobacter pylori isolates to the complete genome sequence of an isolate associated with MALT lymphoma.

BACKGROUND: Helicobacter pylori infection is associated with several gastro-duodenal inflammatory diseases of various levels of severity. To determine whether certain combinations of genetic markers can be used to predict the clinical source of the infection, we analyzed well documented and geographically homogenous clinical isolates using a comparative genomics approach. RESULTS: A set of 254 H. pylori genes was used to perform array-based comparative genomic hybridization among 120 French H. pylori strains associated with chronic gastritis (n = 33), duodenal ulcers (n = 27), intestinal metaplasia (n = 17) or gastric extra-nodal marginal zone B-cell MALT lymphoma (n = 43). Hierarchical cluster analyses of the DNA hybridization values allowed us to identify a homogeneous subpopulation of strains that clustered exclusively with cagPAI minus MALT lymphoma isolates. The genome sequence of B38, a representative of this MALT lymphoma strain-cluster, was completed, fully annotated, and compared with the six previously released H. pylori genomes (i.e. J99, 26695, HPAG1, P12, G27 and Shi470). B38 has the smallest H. pylori genome described thus far (1,576,758 base pairs containing 1,528 CDSs); it contains the vacAs2m2 allele and lacks the genes encoding the major virulence factors (absence of cagPAI, babB, babC, sabB, and homB). Comparative genomics led to the identification of very few sequences that are unique to the B38 strain (9 intact CDSs and 7 pseudogenes). Pair-wise genomic synteny comparisons between B38 and the 6 H. pylori sequenced genomes revealed an almost complete co-linearity, never seen before between the genomes of strain Shi470 (a Peruvian isolate) and B38. CONCLUSION: These isolates are deprived of the main H. pylori virulence factors characterized previously, but are nonetheless associated with gastric neoplasia.

Complete mitochondrial genome sequences of three Nakaseomyces species reveal invasion by palindromic GC clusters and considerable size expansion.

Here we report the sequence of three mitochondrial genomes from yeasts of the Nakaseomyces clade that includes the pathogenic yeast Candida glabrata, namely, that of Kluyveromyces delphensis, Candida castellii and Kluyveromyces bacillisporus. The gene content is equivalent to that of C. glabrata, but reveals the existence of new group I introns in COX1 and CYTB and new potential intronic endonucleases. Gene order is highly rearranged in these genomes, which contain numerous palindromic GC clusters. The more GC nucleotides these elements contain, the longer and more AT-rich are the intergenes containing them, leading to a direct relationship between the number of Gs and Cs within the elements and the size of the genomes. Thus, there is a fivefold difference in size between the smallest and the largest mitochondrial genome, with the largest being the most AT-rich overall. Sequences are available under EMBL accession numbers FM995164, FM995165, and FM995166.

Genome sequence of the saprophyte Leptospira biflexa provides insights into the evolution of Leptospira and the pathogenesis of leptospirosis.

Leptospira biflexa is a free-living saprophytic spirochete present in aquatic environments. We determined the genome sequence of L. biflexa, making it the first saprophytic Leptospira to be sequenced. The L. biflexa genome has 3,590 protein-coding genes distributed across three circular replicons: the major 3,604 chromosome, a smaller 278-kb replicon that also carries essential genes, and a third 74-kb replicon. Comparative sequence analysis provides evidence that L. biflexa is an excellent model for the study of Leptospira evolution; we conclude that 2052 genes (61%) represent a progenitor genome that existed before divergence of pathogenic and saprophytic Leptospira species. Comparisons of the L. biflexa genome with two pathogenic Leptospira species reveal several major findings. Nearly one-third of the L. biflexa genes are absent in pathogenic Leptospira. We suggest that once incorporated into the L. biflexa genome, laterally transferred DNA undergoes minimal rearrangement due to physical restrictions imposed by high gene density and limited presence of transposable elements. In contrast, the genomes of pathogenic Leptospira species undergo frequent rearrangements, often involving recombination between insertion sequences. Identification of genes common to the two pathogenic species, L. borgpetersenii and L. interrogans, but absent in L. biflexa, is consistent with a role for these genes in pathogenesis. Differences in environmental sensing capacities of L. biflexa, L. borgpetersenii, and L. interrogans suggest a model which postulates that loss of signal transduction functions in L. borgpetersenii has impaired its survival outside a mammalian host, whereas L. interrogans has retained environmental sensory functions that facilitate disease transmission through water.