Comparison of genome sequencing technology and assembly methods for the analysis of a GC-rich bacterial genome

Triplex real-time PCR ZKIR-T assay for simultaneous detection of the Klebsiella pneumoniae species complex and identification of K. pneumoniae sensu stricto

Klebsiella pneumoniae species complex (KpSC) members, including the most important species K. pneumoniae (phylogroup Kp1 of the KpSC), are important opportunistic pathogens that display increasing rates of antimicrobial resistance worldwide. As they are widespread in food and the environment, there is a need for fast, sensitive, and reliable methods to detect KpSC members in complex matrices. Previously, the ZKIR real-time PCR assay was developed to detect all KpSC members without distinction. Given that Kp1 is the clinically most significant phylogroup of the KpSC, here, we aimed to simultaneously identify Kp1 while detecting all KpSC members. Three TaqMan probes were developed and used: the Kp1 probe to specifically identify this phylogroup; the zkir P1 probe to detect phylogroups Kp1-Kp5 and Kp7; and the zkir P2 probe to detect phylogroup Kp6. The new triplex assay was tested on a total of 95 KpSC and 19 non-KpSC strains from various sources, representing the different phylogroups as defined by whole genome sequencing. The results showed almost complete specificity, as the expected PCR results were obtained for 112 (98%) strains. The new triplex real-time PCR assay, called ZKIR-T, enables the detection of all KpSC taxa while discriminating Kp1, which will be useful for rapid screening and to focus downstream analyses on chosen phylogroups of the KpSC.

IMPORTANCE

The pathogens of the Klebsiella pneumoniae species complex are widespread in food and animals and are among the main pathogens responsible for multidrug resistant infections in humans. In this study, we developed a highly sensitive detection assay that enables detection of this group of bacteria, with the simultaneous identification of the most common and clinically important species. This triplex one-reaction assay was shown to be highly sensitive and precise, enabling fast screening of varied samples for the presence of KpSC and K. pneumoniae sensu stricto.

Karyon: a computational framework for the diagnosis of hybrids, aneuploids, and other nonstandard architectures in genome assemblies

BACKGROUND

Recent technological developments have made genome sequencing and assembly highly accessible and widely used. However, the presence in sequenced organisms of certain genomic features such as high heterozygosity, polyploidy, aneuploidy, heterokaryosis, or extreme compositional biases can challenge current standard assembly procedures and result in highly fragmented assemblies. Hence, we hypothesized that genome databases must contain a nonnegligible fraction of low-quality assemblies that result from such type of intrinsic genomic factors.

FINDINGS

Here we present Karyon, a Python-based toolkit that uses raw sequencing data and de novo genome assembly to assess several parameters and generate informative plots to assist in the identification of nonchanonical genomic traits. Karyon includes automated de novo genome assembly and variant calling pipelines. We tested Karyon by diagnosing 35 highly fragmented publicly available assemblies from 19 different Mucorales (Fungi) species.

CONCLUSIONS

Our results show that 10 (28.57%) of the assemblies presented signs of unusual genomic configurations, suggesting that these are common, at least for some lineages within the Fungi.

Plasmids Bring Additional Capabilities to Caulobacter Isolates

Caulobacter is a well-studied bacterial genus, but little is known about the plasmids that are found in some wild Caulobacter isolates. We used bioinformatic approaches to identify nine plasmids from seven different Caulobacter strains and grouped them based on their size and the similarity of their repABC, parAB, and mobAB genes. Protein pathway analysis of the genes on the K31p1 and K31p2 plasmids showed many metabolic pathways that would enhance the metabolic versatility of the host strain. In contrast, the CB4 plasmid contained 21 heavy metal resistance genes with the majority coding for proteins that enhance copper resistance. Growth assays of C. henricii CB4 demonstrated increased copper resistance and quantitative PCR showed an increase in the expression of eight heavy metal genes when induced with copper.

Evolutionary history of Caulobacter toxin-antitoxin systems

Toxin-antitoxin (TA) systems have been studied in many bacterial genera, but a clear understanding of the evolutionary trajectory of TA operons has not emerged. To address this issue, I identified 42 distinct TA operons in three genomes that represent the three branches of the Caulobacter phylogenetic tree. The location of each operon was then examined to determine if the operon was present in eight additional Caulobacter genomes. Most of the 42 TA operons were present at the same chromosomal location in genomes that represent at least two different branches of the Caulobacter phylogenetic tree. This result indicates that the chromosomal location of TA operons is conserved over evolutionary time scales. One the other hand, there were 177 instances where a TA operon was not present at an expected chromosomal location and four instances where only the antitoxin gene was present. Thus, the variable number of TA operons found in each genome appears to be due primarily to the loss of TA operons, and the addition of new TA operons to a genome was relatively rare. An additional feature of the TA operons was that they seemed to accumulate mutations faster than the adjacent genes.

Novel Caulobacter bacteriophages illustrate the diversity of the podovirus genus Rauchvirus

The podovirus BPP-1 is currently the only member of the Podovirus genus Rauchvirus. Here, we describe three new Caulobacter bacteriophages (Jess A, SR18, and RW) that show genetic similarity to BPP-1 but have many different genetic and structural features that differentiate them from BPP-1. Jess A and SR18 are closely related to each other and should be considered two members of a new species. They share a similar gene order with BPP-1. However, they do not appear to form lysogens or have the tropism switching mechanism that has been described for BPP-1. Bacteriophage RW also exhibits some homology to BPP-1. However, it is quite different from the other three phages, and we propose that it should be considered a representative of a third species of the genus Rauchvirus. Taken together, the differences among these four members of the genus Rauchvirus indicate that this divergent genus has a long evolutionary history and that there are many more rauchviruses waiting to be discovered.

Klenkia terrae resistant to DNA extraction in germ-free mice stools illustrates the extraction pitfall faced by metagenomics

Over the past decade, metagenomics has become the preferred method for exploring complex microbiota such as human gut microbiota. However, several bias affecting the results of microbiota composition, such as those due to DNA extraction, have been reported. These bias have been confirmed with the development of culturomics technique. In the present study, we report the contamination of a gnotobiotic mice unit with a bacterium first detected by gram staining. Scanning electron microscopy and transmission electron microscopy permitted to detect a bacterium with a thick cell wall. However, in parallel, the first attempt to identify and culture this bacterium by gene amplification and metagenomics of universal 16S rRNA failed. Finally, the isolation in culture of a fastidious bacterium not detected by using universal PCR was successfully achieved by using a BCYE agar plate with CO₂ atmosphere at 30 °C. We performed genome sequencing of this bacterium using a strong extraction procedure. The genomic comparison allowed us to classify this bacterium as Klenkia terrae. And finally, it was also detected in the stool and kibble that caused the contamination by using specific qPCR against this bacterium. The elucidation of this contamination provides additional evidence that DNA extraction could be a bias for the study of the microbiota. Currently, most studies that strive to analyze and compare the gut microbiota are based on metagenomics. In a gnotobiotic mice unit contaminated with the fastidious Actinobacteria Klenkia terrae, standard culture, 16S rRNA gene amplification and metagenomics failed to identify the micro-organism observed in stools by gram-staining. Only a procedure based on culturomics allowed us to identify this bacterium and to elucidate the mode of contamination of the gnotobiotic mice unit through diet.

lordFAST: sensitive and Fast Alignment Search Tool for LOng noisy Read sequencing Data

Motivation

Recent advances in genomics and precision medicine have been made possible through the application of high throughput sequencing (HTS) to large collections of human genomes. Although HTS technologies have proven their use in cataloging human genome variation, computational analysis of the data they generate is still far from being perfect. The main limitation of Illumina and other popular sequencing technologies is their short read length relative to the lengths of (common) genomic repeats. Newer (single molecule sequencing - SMS) technologies such as Pacific Biosciences and Oxford Nanopore are producing longer reads, making it theoretically possible to overcome the difficulties imposed by repeat regions. Unfortunately, because of their high sequencing error rate, reads generated by these technologies are very difficult to work with and cannot be used in many of the standard downstream analysis pipelines. Note that it is not only difficult to find the correct mapping locations of such reads in a reference genome, but also to establish their correct alignment so as to differentiate sequencing errors from real genomic variants. Furthermore, especially since newer SMS instruments provide higher throughput, mapping and alignment need to be performed much faster than before, maintaining high sensitivity.

Results

We introduce lordFAST, a novel long-read mapper that is specifically designed to align reads generated by PacBio and potentially other SMS technologies to a reference. lordFAST not only has higher sensitivity than the available alternatives, it is also among the fastest and has a very low memory footprint.

Availability and implementation

lordFAST is implemented in C++ and supports multi-threading. The source code of lordFAST is available at https://github.com/vpc-ccg/lordfast.

Supplementary information

Supplementary data are available at Bioinformatics online.

Analysis of the Complete Genome Sequence of a Novel, Pseudorabies Virus Strain Isolated in Southeast Europe

Background

Pseudorabies virus (PRV) is the causative agent of Aujeszky's disease giving rise to significant economic losses worldwide. Many countries have implemented national programs for the eradication of this virus. In this study, long-read sequencing was used to determine the nucleotide sequence of the genome of a novel PRV strain (PRV-MdBio) isolated in Serbia.

Results

In this study, a novel PRV strain was isolated and characterized. PRV-MdBio was found to exhibit similar growth properties to those of another wild-type PRV, the strain Kaplan. Single-molecule real-time (SMRT) sequencing has revealed that the new strain differs significantly in base composition even from strain Kaplan, to which it otherwise exhibits the highest similarity. We compared the genetic composition of PRV-MdBio to strain Kaplan and the China reference strain Ea and obtained that radical base replacements were the most common point mutations preceding conservative and silent mutations. We also found that the adaptation of PRV to cell culture does not lead to any tendentious genetic alteration in the viral genome.

Conclusion

PRV-MdBio is a wild-type virus, which differs in base composition from other PRV strains to a relatively large extent.

The Microbiological Characteristics of Carbapenem-Resistant Enterobacteriaceae Carrying the mcr-1 Gene

Objectives: This study aims to assess the prevalence of the mcr-1 gene among carbapenem-resistant Enterobacteriaceae (CRE) isolated from clinical specimens and to further investigate the clinical significance and microbiological characteristics of CRE carrying the mcr-1 gene. Methods: Four hundred and twenty-three CRE isolates were screened for the presence of the mcr-1 gene. After identification, their clinical significance, antibiotic susceptibility, and antibiotic resistance mechanisms including the ESBL gene, carbapenemase gene, outer membrane protein (OMP), and plasmid sequencing were assessed. Results: Only four (0.9%) isolates of carbapenem-resistant Escherichia coli (E. coli) were found to carry the mcr-1 gene and demonstrated different pulsed-field gel electrophoresis (PFGE) patterns and sequence types (ST). While one patient was considered as having mcr-1-positive carbapenem-resistant E. coli (CREC) colonization, the other three mcr-1-positive CREC-related infections were classified as nosocomial infections. Only amikacin and tigecycline showed good in vitro activity against these four isolates, and three of them had a minimum inhibitory concentration with colistin of ≥4 mg/L. In the colistin-susceptible isolate, mcr-1 was nonfunctional due to the insertion of another gene. In addition, all of the mcr-1-positive CREC contained various resistant genes, such as AmpC_CMY, bla_NDM, bla_TEM, bla_SHV, and bla_CTX. In addition, one strain (EC1037) had loss of the OMP. Conclusions: The emergence of the mcr-1 gene among CRE, especially E. coli, remains worth our attention due to its resistance to most antibiotics, and a further national survey is warranted.

Simultaneous three Enterobacteriaceae with different bla NDM-1-encoding plasmids in a patient transferred from mainland China to Taiwan

New-Delhi metallo-β-lactamase1 (NDM-1) Enterobacteriaceae are increasing worldwide. Herein, we describe a single patient who carried three unusual NDM-1 carbapenem-resistant Enterobacteriaceae – Enterobacter cloacae (E. cloacae) yielded from a urine specimen and Klebsiella pneumoniae (K. pneumoniae) and Escherichia coli (E. coli) from stool specimens. For E. cloacae, its bla NDM-1-encoding plasmid was pKP04NDM with a size of ~54 kb replicons with an IncN backbone. For K. pneumoniae, its bla_NDM-1-encoding plasmid was pNDM-BTR with a size of ~59.6 kb and belonged to IncN. For E. coli, its main bla_NDM-1-encoding plasmid was pIMP-HK1500, and the NDM-1 gene was obtained from a part of pNDM-BTR (8439 bp). These three clinical strains are reported for the first time and are assumed to be imported from mainland China to Taiwan. The three different plasmids were never reported in K. pneumoniae, E. coli, and Citrobacter spp before. Owing to their associated multidrug resistance, appropriate measures of periodic, targeted surveillance, and development of new antimicrobial agents are urgently needed.

Genome Comparisons of Wild Isolates of Caulobacter crescentus Reveal Rates of Inversion and Horizontal Gene Transfer

Since previous interspecies comparisons of Caulobacter genomes have revealed extensive genome rearrangements, we decided to compare the nucleotide sequences of four C. crescentus genomes, NA1000, CB1, CB2, and CB13. To accomplish this goal, we used PacBio sequencing technology to determine the nucleotide sequence of the CB1, CB2, and CB13 genomes, and obtained each genome sequence as a single contig. To correct for possible sequencing errors, each genome was sequenced twice. The only differences we observed between the two sets of independently determined sequences were random omissions of a single base in a small percentage of the homopolymer regions where a single base is repeated multiple times. Comparisons of these four genomes indicated that horizontal gene transfer events that included small numbers of genes occurred at frequencies in the range of 10^-3 to 10^-4 insertions per generation. Large insertions were about 100 times less frequent. Also, in contrast to previous interspecies comparisons, we found no genome rearrangements when the closely related NA1000, CB1, and CB2 genomes were compared, and only eight inversions and one translocation when the more distantly related CB13 genome was compared to the other genomes. Thus, we estimate that inversions occur at a rate of one per 10 to 12 million generations in Caulobacter genomes. The inversions seem to be complex events that include the simultaneous creation of indels.

Complete Genome Sequence of a Wild-Type Isolate of Caulobacter vibrioides Strain CB2

The complete genome of Caulobacter vibrioides strain CB2 consists of a 4,123,726-bp chromosome, a GC content of 67.2%, and 3,896 coding DNA sequences. It has no rearrangements but numerous indels relative to the reference NA1000 genome.

The complete genome of Caulobacter vibrioides strain CB2 consists of a 4,123,726-bp chromosome, a GC content of 67.2%, and 3,896 coding DNA sequences. It has no rearrangements but numerous indels relative to the reference NA1000 genome. This will allow us to study the impact of horizontal gene transfer on caulobacter genomes.

Complete Genome Sequence of a Wild-Type Isolate of Caulobacter vibrioides Strain CB1

The complete genome sequence of Caulobacter vibrioides strain CB1 consists of a chromosome of 4,137,285 bp, with a GC content of 67.2% and 3,990 coding DNA sequences. This strain contains the typical genome rearrangement that is characteristic of the Caulobacter strains that are currently sequenced.

The complete genome sequence of Caulobacter vibrioides strain CB1 consists of a chromosome of 4,137,285 bp, with a GC content of 67.2% and 3,990 coding DNA sequences. This strain contains the typical genome rearrangement that is characteristic of the Caulobacter strains that are currently sequenced. However, this strain is so closely related to sequenced strain NA1000 that rearrangements were minimal. This will allow further clarification of the causes of rearrangements in the species.

Achieving Accurate Sequence and Annotation Data for Caulobacter vibrioides CB13

Annotated sequence data are instrumental in nearly all realms of biology. However, the advent of next-generation sequencing has rapidly facilitated an imbalance between accurate sequence data and accurate annotation data. To increase the annotation accuracy of the Caulobacter vibrioides CB13b1a (CB13) genome, we compared the PGAP and RAST annotations of the CB13 genome. A total of 64 unique genes were identified in the PGAP annotation that were either completely or partially absent in the RAST annotation, and a total of 16 genes were identified in the RAST annotation that were not included in the PGAP annotation. Moreover, PGAP identified 73 frameshifted genes and 22 genes with an internal stop. In contrast, RAST annotated the larger segment of these frameshifted genes without indicating a change in reading frame may have occurred. The RAST annotation did not include any genes with internal stop codons, since it chose start codons that were after the internal stop. To confirm the discrepancies between the two annotations and verify the accuracy of the CB13 genome sequence data, we re-sequenced and re-annotated the entire genome and obtained an identical sequence, except in a small number of homopolymer regions. A genome sequence comparison between the two versions allowed us to determine the correct number of bases in each homopolymer region, which eliminated frameshifts for 31 genes annotated as frameshifted genes and removed 24 pseudogenes from the PGAP annotation. Both annotation systems correctly identified genes that were missed by the other system. In addition, PGAP identified conserved gene fragments that represented the beginning of genes, but it employed no corrective method to adjust the reading frame of frameshifted genes or the start sites of genes harboring an internal stop codon. In doing so, the PGAP annotation identified a large number of pseudogenes, which may reflect evolutionary history but likely do not produce gene products. These results demonstrate that re-sequencing and annotation comparisons can be used to increase the accuracy of genomic data and the corresponding gene annotation.

Comparative Genomic Analysis of Two Clonally Related Multidrug Resistant Mycobacterium tuberculosis by Single Molecule Real Time Sequencing

Background: Multidrug-resistant tuberculosis (MDR-TB) is posing a major threat to global TB control. In this study, we focused on two consecutive MDR-TB isolated from the same patient before and after the initiation of anti-TB treatment. To better understand the genomic characteristics of MDR-TB, Single Molecule Real-Time (SMRT) Sequencing and comparative genomic analyses was performed to identify mutations that contributed to the stepwise development of drug resistance and growth fitness in MDR-TB under in vivo challenge of anti-TB drugs. Result: Both pre-treatment and post-treatment strain demonstrated concordant phenotypic and genotypic susceptibility profiles toward rifampicin, pyrazinamide, streptomycin, fluoroquinolones, aminoglycosides, cycloserine, ethionamide, and para-aminosalicylic acid. However, although both strains carried identical missense mutations at rpoB S531L, inhA C-15T, and embB M306V, MYCOTB Sensititre assay showed that the post-treatment strain had 16-, 8-, and 4-fold elevation in the minimum inhibitory concentrations (MICs) toward rifabutin, isoniazid, and ethambutol respectively. The results have indicated the presence of additional resistant-related mutations governing the stepwise development of MDR-TB. Further comparative genomic analyses have identified three additional polymorphisms between the clinical isolates. These include a single nucleotide deletion at nucleotide position 360 of rv0888 in pre-treatment strain, and a missense mutation at rv3303c (lpdA) V44I and a 6-bp inframe deletion at codon 67-68 in rv2071c (cobM) in the post-treatment strain. Multiple sequence alignment showed that these mutations were occurring at highly conserved regions among pathogenic mycobacteria. Using structural-based and sequence-based algorithms, we further predicted that the mutations potentially have deleterious effect on protein function. Conclusion: This is the first study that compared the full genomes of two clonally-related MDR-TB clinical isolates during the course of anti-TB treatment. Our work has demonstrated the robustness of SMRT Sequencing in identifying mutations among MDR-TB clinical isolates. Comparative genome analysis also suggested novel mutations at rv0888, lpdA, and cobM that might explain the difference in antibiotic resistance and growth pattern between the two MDR-TB strains.

CoLoRMap: Correcting Long Reads by Mapping short reads

MOTIVATION

Second generation sequencing technologies paved the way to an exceptional increase in the number of sequenced genomes, both prokaryotic and eukaryotic. However, short reads are difficult to assemble and often lead to highly fragmented assemblies. The recent developments in long reads sequencing methods offer a promising way to address this issue. However, so far long reads are characterized by a high error rate, and assembling from long reads require a high depth of coverage. This motivates the development of hybrid approaches that leverage the high quality of short reads to correct errors in long reads.

RESULTS

We introduce CoLoRMap, a hybrid method for correcting noisy long reads, such as the ones produced by PacBio sequencing technology, using high-quality Illumina paired-end reads mapped onto the long reads. Our algorithm is based on two novel ideas: using a classical shortest path algorithm to find a sequence of overlapping short reads that minimizes the edit score to a long read and extending corrected regions by local assembly of unmapped mates of mapped short reads. Our results on bacterial, fungal and insect data sets show that CoLoRMap compares well with existing hybrid correction methods.

AVAILABILITY AND IMPLEMENTATION

The source code of CoLoRMap is freely available for non-commercial use at https://github.com/sfu-compbio/colormap

CONTACT

ehaghshe@sfu.ca or cedric.chauve@sfu.ca

SUPPLEMENTARY INFORMATION

Supplementary data are available at Bioinformatics online.

Long-Read Isoform Sequencing Reveals a Hidden Complexity of the Transcriptional Landscape of Herpes Simplex Virus Type 1

In this study, we used the amplified isoform sequencing technique from Pacific Biosciences to characterize the poly(A)⁺ fraction of the lytic transcriptome of the herpes simplex virus type 1 (HSV-1). Our analysis detected 34 formerly unidentified protein-coding genes, 10 non-coding RNAs, as well as 17 polycistronic and complex transcripts. This work also led us to identify many transcript isoforms, including 13 splice and 68 transcript end variants, as well as several transcript overlaps. Additionally, we determined previously unascertained transcriptional start and polyadenylation sites. We analyzed the transcriptional activity from the complementary DNA strand in five convergent HSV gene pairs with quantitative RT-PCR and detected antisense RNAs in each gene. This part of the study revealed an inverse correlation between the expressions of convergent partners. Our work adds new insights for understanding the complexity of the pervasive transcriptional overlaps by suggesting that there is a crosstalk between adjacent and distal genes through interaction between their transcription apparatuses. We also identified transcripts overlapping the HSV replication origins, which may indicate an interplay between the transcription and replication machineries. The relative abundance of HSV-1 transcripts has also been established by using a novel method based on the calculation of sequencing reads for the analysis.

Comparative genomics of Burkholderia multivorans, a ubiquitous pathogen with a highly conserved genomic structure

The natural environment serves as a reservoir of opportunistic pathogens. A well-established method for studying the epidemiology of such opportunists is multilocus sequence typing, which in many cases has defined strains predisposed to causing infection. Burkholderia multivorans is an important pathogen in people with cystic fibrosis (CF) and its epidemiology suggests that strains are acquired from non-human sources such as the natural environment. This raises the central question of whether the isolation source (CF or environment) or the multilocus sequence type (ST) of B. multivorans better predicts their genomic content and functionality. We identified four pairs of B. multivorans isolates, representing distinct STs and consisting of one CF and one environmental isolate each. All genomes were sequenced using the PacBio SMRT sequencing technology, which resulted in eight high-quality B. multivorans genome assemblies. The present study demonstrated that the genomic structure of the examined B. multivorans STs is highly conserved and that the B. multivorans genomic lineages are defined by their ST. Orthologous protein families were not uniformly distributed among chromosomes, with core orthologs being enriched on the primary chromosome and ST-specific orthologs being enriched on the second and third chromosome. The ST-specific orthologs were enriched in genes involved in defense mechanisms and secondary metabolism, corroborating the strain-specificity of these virulence characteristics. Finally, the same B. multivorans genomic lineages occur in both CF and environmental samples and on different continents, demonstrating their ubiquity and evolutionary persistence.

Full-Length Isoform Sequencing Reveals Novel Transcripts and Substantial Transcriptional Overlaps in a Herpesvirus

Whole transcriptome studies have become essential for understanding the complexity of genetic regulation. However, the conventionally applied short-read sequencing platforms cannot be used to reliably distinguish between many transcript isoforms. The Pacific Biosciences (PacBio) RS II platform is capable of reading long nucleic acid stretches in a single sequencing run. The pseudorabies virus (PRV) is an excellent system to study herpesvirus gene expression and potential interactions between the transcriptional units. In this work, non-amplified and amplified isoform sequencing protocols were used to characterize the poly(A⁺) fraction of the lytic transcriptome of PRV, with the aim of a complete transcriptional annotation of the viral genes. The analyses revealed a previously unrecognized complexity of the PRV transcriptome including the discovery of novel protein-coding and non-coding genes, novel mono- and polycistronic transcription units, as well as extensive transcriptional overlaps between neighboring and distal genes. This study identified non-coding transcripts overlapping all three replication origins of the PRV, which might play a role in the control of DNA synthesis. We additionally established the relative expression levels of gene products. Our investigations revealed that the whole PRV genome is utilized for transcription, including both DNA strands in all coding and intergenic regions. The genome-wide occurrence of transcript overlaps suggests a crosstalk between genes through a network formed by interacting transcriptional machineries with a potential function in the control of gene expression.

Conservation of the Essential Genome Among Caulobacter and Brevundimonas Species

When the genomes of Caulobacter isolates NA1000 and K31 were compared, numerous genome rearrangements were observed. In contrast, similar comparisons of closely related species of other bacterial genera revealed nominal rearrangements. A phylogenetic analysis of the 16S rRNA indicated that K31 is more closely related to Caulobacter henricii CB4 than to other known Caulobacters. Therefore, we sequenced the CB4 genome and compared it to all of the available Caulobacter genomes to study genome rearrangements, discern the conservation of the NA1000 essential genome, and address concerns about using 16S rRNA to group Caulobacter species. We also sequenced the novel bacteria, Brevundimonas DS20, a representative of the genus most closely related to Caulobacter and used it as part of an outgroup for phylogenetic comparisons. We expected to find that there would be fewer rearrangements when comparing more closely related Caulobacters. However, we found that relatedness was not correlated with the amount of observed "genome scrambling." We also discovered that nearly all of the essential genes previously identified for C. crescentus are present in the other Caulobacter genomes and in the Brevundimonas genomes as well. However, a few of these essential genes were only found in NA1000, and some were missing in a combination of one or more species, while other proteins were 100 % identical across species. Also, phylogenetic comparisons of highly conserved genomic regions revealed clades similar to those identified by 16S rRNA-based phylogenies, verifying that 16S rRNA sequence comparisons are a valid method for grouping Caulobacters.

Comparison of Sample Preparation Methods Used for the Next-Generation Sequencing of Mycobacterium tuberculosis

The advent and widespread application of next-generation sequencing (NGS) technologies to the study of microbial genomes has led to a substantial increase in the number of studies in which whole genome sequencing (WGS) is applied to the analysis of microbial genomic epidemiology. However, microorganisms such as Mycobacterium tuberculosis (MTB) present unique problems for sequencing and downstream analysis based on their unique physiology and the composition of their genomes. In this study, we compare the quality of sequence data generated using the Nextera and TruSeq isolate preparation kits for library construction prior to Illumina sequencing-by-synthesis. Our results confirm that MTB NGS data quality is highly dependent on the purity of the DNA sample submitted for sequencing and its guanine-cytosine content (or GC-content). Our data additionally demonstrate that the choice of library preparation method plays an important role in mitigating downstream sequencing quality issues. Importantly for MTB, the Illumina TruSeq library preparation kit produces more uniform data quality than the Nextera XT method, regardless of the quality of the input DNA. Furthermore, specific genomic sequence motifs are commonly missed by the Nextera XT method, as are regions of especially high GC-content relative to the rest of the MTB genome. As coverage bias is highly undesirable, this study illustrates the importance of appropriate protocol selection when performing NGS studies in order to ensure that sound inferences can be made regarding mycobacterial genomes.

A comparison of rumen microbial profiles in dairy cows as retrieved by 454 Roche and Ion Torrent (PGM) sequencing platforms

Next generation sequencing (NGS) technology is a widely accepted tool used by microbial ecologists to explore complex microbial communities in different ecosystems. As new NGS platforms continue to become available, it becomes imperative to compare data obtained from different platforms and analyze their effect on microbial community structure. In the present study, we compared sequencing data from both the 454 and Ion Torrent (PGM) platforms on the same DNA samples obtained from the rumen of dairy cows during their transition period. Despite the substantial difference in the number of reads, error rate and length of reads among both platforms, we identified similar community composition between the two data sets. Procrustes analysis revealed similar correlations (M (2) = 0.319; P = 0.001) in the microbial community composition between the two platforms. Both platforms revealed the abundance of the same bacterial phyla which were Bacteroidetes and Firmicutes; however, PGM recovered an additional four phyla. Comparisons made at the genus level by each platforms revealed differences in only a few genera such as Prevotella, Ruminococcus, Succiniclasticum and Treponema (p < 0.05; chi square test). Collectively, we conclude that the output generated from PGM and 454 yielded concurrent results, provided stringent bioinformatics pipelines are employed.