Molecular analysis of asymptomatic bacteriuria Escherichia coli strain VR50 reveals adaptation to the urinary tract by gene acquisition.

Urinary tract infections (UTIs) are among the most common infectious diseases of humans, with Escherichia coli responsible for >80% of all cases. One extreme of UTI is asymptomatic bacteriuria (ABU), which occurs as an asymptomatic carrier state that resembles commensalism. To understand the evolution and molecular mechanisms that underpin ABU, the genome of the ABU E. coli strain VR50 was sequenced. Analysis of the complete genome indicated that it most resembles E. coli K-12, with the addition of a 94-kb genomic island (GI-VR50-pheV), eight prophages, and multiple plasmids. GI-VR50-pheV has a mosaic structure and contains genes encoding a number of UTI-associated virulence factors, namely, Afa (afimbrial adhesin), two autotransporter proteins (Ag43 and Sat), and aerobactin. We demonstrated that the presence of this island in VR50 confers its ability to colonize the murine bladder, as a VR50 mutant with GI-VR50-pheV deleted was attenuated in a mouse model of UTI in vivo. We established that Afa is the island-encoded factor responsible for this phenotype using two independent deletion (Afa operon and AfaE adhesin) mutants. E. coli VR50afa and VR50afaE displayed significantly decreased ability to adhere to human bladder epithelial cells. In the mouse model of UTI, VR50afa and VR50afaE displayed reduced bladder colonization compared to wild-type VR50, similar to the colonization level of the GI-VR50-pheV mutant. Our study suggests that E. coli VR50 is a commensal-like strain that has acquired fitness factors that facilitate colonization of the human bladder.

Genome analysis and CRISPR typing of Salmonella enterica serovar Virchow.

BACKGROUND: Salmonella enterica subsp. enterica serovar Virchow has been recognized as a significant health burden in Asia, Australia and Europe. In addition to its global distribution, S. Virchow is clinically significant due to the frequency at which it causes invasive infections and its association with outbreaks arising from food-borne transmission. Here, we examine the genome of an invasive isolate of S. Virchow SVQ1 (phage type 8) from an outbreak in southeast Queensland, Australia. In addition to identifying new potential genotyping targets that could be used for discriminating between S. Virchow strains in outbreak scenarios, we also aimed to carry out a comprehensive comparative analysis of the S. Virchow genomes. RESULTS: Genome comparisons between S. Virchow SVQ1 and S. Virchow SL491, a previously published strain, identified a high degree of genomic similarity between the two strains with fewer than 200 single nucleotide differences. Clustered Regularly Interspaced Palindromic Repeats (CRISPR) regions were identified as a highly variable region that could be used to discriminate between S. Virchow isolates. We amplified and sequenced the CRISPR regions of fifteen S. Virchow isolates collected from seven different outbreaks across Australia. We observed three allelic types of the CRISPR region from these isolates based on the presence/absence of the spacers and were able to discriminate S. Virchow phage type 8 isolates originating from different outbreaks. A comparison with 27 published Salmonella genomes found that the S. Virchow SVQ1 genome encodes 11 previously described Salmonella Pathogenicity Islands (SPI), as well as additional genomic islands including a remnant integrative conjugative element that is distinct from SPI-7. In addition, the S. Virchow genome possesses a novel prophage that encodes the Type III secretion system effector protein SopE, a key Salmonella virulence factor. The prophage shares very little similarity to the SopE prophages found in other Salmonella serovars suggesting an independent acquisition of sopE. CONCLUSIONS: The availability of this genome will serve as a genome template and facilitate further studies on understanding the virulence and global distribution of the S. Virchow serovar, as well as the development of genotyping methods for outbreak investigations.

Draft genome sequence of the male-killing Wolbachia strain wBol1 reveals recent horizontal gene transfers from diverse sources.

BACKGROUND: The endosymbiont Wolbachia pipientis causes diverse and sometimes dramatic phenotypes in its invertebrate hosts. Four Wolbachia strains sequenced to date indicate that the constitution of the genome is dynamic, but these strains are quite divergent and do not allow resolution of genome diversification over shorter time periods. We have sequenced the genome of the strain wBol1-b, found in the butterfly Hypolimnas bolina, which kills the male offspring of infected hosts during embyronic development and is closely related to the non-male-killing strain wPip from Culex pipiens. RESULTS: The genomes of wBol1-b and wPip are similar in genomic organisation, sequence and gene content, but show substantial differences at some rapidly evolving regions of the genome, primarily associated with prophage and repetitive elements. We identified 44 genes in wBol1-b that do not have homologs in any previously sequenced strains, indicating that Wolbachia's non-core genome diversifies rapidly. These wBol1-b specific genes include a number that have been recently horizontally transferred from phylogenetically distant bacterial taxa. We further report a second possible case of horizontal gene transfer from a eukaryote into Wolbachia. CONCLUSIONS: Our analyses support the developing view that many endosymbiotic genomes are highly dynamic, and are exposed and receptive to exogenous genetic material from a wide range of sources. These data also suggest either that this bacterial species is particularly permissive for eukaryote-to-prokaryote gene transfers, or that these transfers may be more common than previously believed. The wBol1-b-specific genes we have identified provide candidates for further investigations of the genomic bases of phenotypic differences between closely-related Wolbachia strains.

Regulated post-transcriptional RNA cleavage diversifies the eukaryotic transcriptome.

The complexity of the eukaryotic transcriptome is generated by the interplay of transcription initiation, termination, alternative splicing, and other forms of post-transcriptional modification. It was recently shown that RNA transcripts may also undergo cleavage and secondary 5' capping. Here, we show that post-transcriptional cleavage of RNA contributes to the diversification of the transcriptome by generating a range of small RNAs and long coding and noncoding RNAs. Using genome-wide histone modification and RNA polymerase II occupancy data, we confirm that the vast majority of intraexonic CAGE tags are derived from post-transcriptional processing. By comparing exonic CAGE tags to tissue-matched PARE data, we show that the cleavage and subsequent secondary capping is regulated in a developmental-stage- and tissue-specific manner. Furthermore, we find evidence of prevalent RNA cleavage in numerous transcriptomic data sets, including SAGE, cDNA, small RNA libraries, and deep-sequenced size-fractionated pools of RNA. These cleavage products include mRNA variants that retain the potential to be translated into shortened functional protein isoforms. We conclude that post-transcriptional RNA cleavage is a key mechanism that expands the functional repertoire and scope for regulatory control of the eukaryotic transcriptome.

Global analysis of the mammalian RNA degradome reveals widespread miRNA-dependent and miRNA-independent endonucleolytic cleavage.

The Ago2 component of the RNA-induced silencing complex (RISC) is an endonuclease that cleaves mRNAs that base pair with high complementarity to RISC-bound microRNAs. Many examples of such direct cleavage have been identified in plants, but not in vertebrates, despite the conservation of catalytic capacity in vertebrate Ago2. We performed parallel analysis of RNA ends (PAREs), a deep sequencing approach that identifies 5'-phosphorylated, polyadenylated RNAs, to detect potential microRNA-directed mRNA cleavages in mouse embryo and adult tissues. We found that numerous mRNAs are potentially targeted for cleavage by endogenous microRNAs, but at very low levels relative to the mRNA abundance, apart from miR-151-5p-guided cleavage of the N4BP1 mRNA. We also find numerous examples of non-miRNA-directed cleavage, including cleavage of a group of mRNAs within a CA-repeat consensus sequence. The PARE analysis also identified many examples of adenylated small non-coding RNAs, including microRNAs, tRNA processing intermediates and various other small RNAs, consistent with adenylation being part of a widespread proof-reading and/or degradation pathway for small RNAs.

On measuring miRNAs after transient transfection of mimics or antisense inhibitors.

The ability to alter microRNA (miRNA) abundance is crucial for studying miRNA function. To achieve this there is widespread use of both exogenous double-stranded miRNA mimics for transient over-expression, and single stranded antisense RNAs (antimiRs) for miRNA inhibition. The success of these manipulations is often assessed using qPCR, but this does not accurately report the level of functional miRNA. Here, we draw attention to this discrepancy, which is overlooked in many published reports. We measured the functionality of exogenous miRNA by comparing the total level of transfected miRNA in whole cell extracts to the level of miRNA bound to Argonaute following transfection and show that the supraphysiological levels of transfected miRNA frequently seen using qPCR do not represent the functional levels, because the majority of transfected RNA that is detected is vesicular and not accessible for loading into Argonaute as functionally active miRNAs. In the case of microRNA inhibition by transient transfection with antisense inhibitors, there is also the potential for discrepancy, because following cell lysis the abundant inhibitor levels from cellular vesicles can directly interfere with the PCR reaction used to measure miRNA level.

New plasmids and putative virulence factors from the draft genome of an Australian clinical isolate of Photorhabdus asymbiotica.

Clinical isolates of Photorhabdus asymbiotica have been recovered from patients in both the United States of America and Australia, and the full sequence of P. asymbiotica ATCC43949 from the United States has been reported recently. In contrast to other bacteria in the genus that only infect insects, P. asymbiotica strains are able to infect both insects and humans. Using a combination of Solexa (Illumina) and 454 Life Sciences (Roche) sequence data in different assembly pipelines, we report on a draft genome sequence of a strain of P. asymbiotica recovered from a patient from Kingscliff, Australia. The best assembly yielded an N50 scaffold size of 288 627 base pairs (bp) with >88.6% of the predicted genome covered by scaffolds over 100 000 bp. One of the central differences found between this Australian isolate and the US isolate is the presence of an additional plasmid, pPAA3. This plasmid is similar to pCRY from Yersinia pestis, the causative agent of bubonic plague, and the presence of pPAA3 may account for the increased virulence of Australian isolates both against tissue culture cells and infected patients. The genome of the Kingscliff strain also contains several genomic differences from the US isolate, whose potential significance in virulence against both humans and insects is discussed.