Comparative genomics and understanding of microbial biology

Genomic variations in Mycobacterium tuberculosis from the lungs and blood of HIV-infected individuals in Uganda: insights into compartmentalization

Mycobacterium tuberculosis (MTB) clinical strains are relatively varied at the genome level. This in-silico study analyzed genomic differences between MTB isolates from the blood and lungs of TB-HIV positive cohorts in Uganda. The hypothesis was that isolates from the blood have distinct SNPs and INDELs that make them better survivors. Twenty-four MTB-blood and -lung sequences were aligned against the H37Rv reference genome and analyzed using BWA-MEM, IGV, SAMtools, FreeBayes, and SnpEff. Comparative analysis revealed that MTB-blood isolates had 11 virulence genes with distinctive non-synonymous SNPs involved in increasing colony-forming units, lowering host survival, enhancing tissue pathology, and allowing for human host persistence. The majority of INDELs were found in non-virulence genes, with the remainder in both MTB-blood and -lung sequences. The study suggests that MTB-blood isolates have distinctive SNPs that explain their capacity to persist outside of the lungs. However, further research is needed to understand the significance of these SNPs in the pathogenesis of MTB.

Impact

Mycobacterium tuberculosis (MTB) clinical strains have high genomic variability, and there is a knowledge gap on the genomic differences between MTB isolates from the blood and lungs of TB-HIV positive patients in Uganda. This study found that MTB-blood isolates had 11 virulence genes with distinctive non-synonymous SNPs that may contribute to their capacity to persist outside of the lungs. These findings provide insight into the genomic basis of MTB adaptation in different host environments, but further research is needed to fully understand the significance of these SNPs in MTB pathogenesis.

Comparative genome analysis among Variovorax species and genome guided aromatic compound degradation analysis emphasizing 4-hydroxybenzoate degradation in Variovorax sp. PAMC26660

Background

While the genus Variovorax is known for its aromatic compound metabolism, no detailed study of the peripheral and central pathways of aromatic compound degradation has yet been reported. Variovorax sp. PAMC26660 is a lichen-associated bacterium isolated from Antarctica. The work presents the genome-based elucidation of peripheral and central catabolic pathways of aromatic compound degradation genes in Variovorax sp. PAMC26660. Additionally, the accessory, core and unique genes were identified among Variovorax species using the pan genome analysis tool. A detailed analysis of the genes related to xenobiotic metabolism revealed the potential roles of Variovorax sp. PAMC26660 and other species in bioremediation.

Results

TYGS analysis, dDDH, phylogenetic placement and average nucleotide identity (ANI) analysis identified the strain as Variovorax sp. Cell morphology was assessed using scanning electron microscopy (SEM). On analysis of the core, accessory, and unique genes, xenobiotic metabolism accounted only for the accessory and unique genes. On detailed analysis of the aromatic compound catabolic genes, peripheral pathway related to 4-hydroxybenzoate (4-HB) degradation was found among all species while phenylacetate and tyrosine degradation pathways were present in most of the species including PAMC26660. Likewise, central catabolic pathways, like protocatechuate, gentisate, homogentisate, and phenylacetyl-CoA, were also present. The peripheral pathway for 4-HB degradation was functionally tested using PAMC26660, which resulted in the growth using it as a sole source of carbon.

Conclusions

Computational tools for genome and pan genome analysis are important to understand the behavior of an organism. Xenobiotic metabolism-related genes, that only account for the accessory and unique genes infer evolution through events like lateral gene transfer, mutation and gene rearrangement. 4-HB, an aromatic compound present among lichen species is utilized by lichen-associated Variovorax sp. PAMC26660 as the sole source of carbon. The strain holds genes and pathways for its utilization. Overall, this study outlines the importance of Variovorax in bioremediation and presents the genomic information of the species.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-022-08589-3.

In silico comparisons of lipid-related genes between Mycobacterium tuberculosis and BCG vaccine strains

Despite highly variable efficacy, BCG (Bacillus Calmette-Guérin) is the only vaccine available to prevent the tuberculosis (TB). Genomic heterogeneity between attenuated BCG strains and virulent Mycobacterium tuberculosis might help to explain this vaccine’s impaired capacity to induce long-term protection. Here, we investigate the lipid-related genes absent in attenuated BCG strains in order to correlate changes in both lipid metabolism and cell-wall lipid content to vaccine impairment. Whole genome sequences of M. tuberculosis H37Rv and the six most used BCG strains worldwide were aligned and the absent regions functionally categorized. Genomes of the BCG strains showed a total of 14 non-homologous lipid-related genes, including those belonging to mce3 operon, as well as the gene echaA1, which encodes an enoyl-CoA hydratase, and the genes encoding phospholipases PlcA, PlcB and PlcC. Taken together, the depletion of these M. tuberculosis H37Rv genomic regions were associated with marked alterations in lipid-related genes of BCG strains. Such alterations may indicate a dormant-like state and can be determining factors to the vaccine’s inability to induce long-term protection. These lipids can be further evaluated as an adjuvant to boost the current BCG-based vaccine.

Longitudinal Analysis of Gene Expression Changes During Cervical Carcinogenesis Reveals Potential Therapeutic Targets

Despite advances in the treatment of cervical cancer (CC), the prognosis of patients with CC remains to be improved. This study aimed to explore candidate gene targets for CC. CC datasets were downloaded from the Gene Expression Omnibus database. Genes with similar expression trends in varying steps of CC development were clustered using Short Time-series Expression Miner (STEM) software. Gene functions were then analyzed using the Gene Ontology (GO) database and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis. Protein interactions among genes of interest were predicted, followed by drug-target genes and prognosis-associated genes. The expressions of the predicted genes were determined using real-time quantitative polymerase chain reaction (RT-qPCR) and Western blotting. Red and green profiles with upward and downward gene expressions, respectively, were screened using STEM software. Genes with increased expression were significantly enriched in DNA replication, cell-cycle-related biological processes, and the p53 signaling pathway. Based on the predicted results of the Drug-Gene Interaction database, 17 drug-gene interaction pairs, including 3 red profile genes (TOP2A, RRM2, and POLA1) and 16 drugs, were obtained. The Cancer Genome Atlas data analysis showed that high POLA1 expression was significantly correlated with prolonged survival, indicating that POLA1 is protective against CC. RT-qPCR and Western blotting showed that the expressions of TOP2A, RRM2, and POLA1 gradually increased in the multistep process of CC. TOP2A, RRM2, and POLA1 may be targets for the treatment of CC. However, many studies are needed to validate our findings.

Complementation of the Mycoplasma synoviae MS-H vaccine strain with wild-type obg influencing its growth characteristics

The temperature-sensitive (ts+) Mycoplasma synoviae vaccine strain MS-H harbors a non-synonymous mutation which results in Glycine to Arginine substitution at position 123 in the highly conserved glycine-rich motif of Obg-fold in the GTP-binding protein Obg. In-silico analysis of the wild-type and mutant Obgs of M. synoviae has indicated that this amino acid substitution affects structure of the protein, potentially leading to abrogation of Obg function in vivo. Present study was conducted to develop the first expression vector for M. synoviae and to investigate the potential effect(s) of complementation of MS-H vaccine with the wild-type obg from 86079/7NS, the parent strain of MS-H. An oriC vector, pKS-VOTL, harboring the 86079/7NS obg gene, downstream of the variable lipoprotein haemagglutinin (vlhA) gene promoter, also cloned from 86079/7NS, was used to transform MS-H. The plasmid was localised at the chromosomal oriC locus of MS-H without any detectable integration at the chromosomal obg locus. Analysis of the MS-H transformants revealed abundant obg transcripts as well as Obg protein, when compared to the MS-H transformed with a similar vector, pMAS-LoriC, lacking obg coding sequence. The MS-H transformants complemented with wild-type Obg maintained their original temperature-sensitivity phenotype (consistent with MS-H vaccine) but, when compared to the MS-H transformed with pMAS-LoriC, had significantly higher (p < 0.05) growth rate and viability at the permissive (33°C) and non-permissive temperature (39.5°C), respectively. Analysis of Obg expression in MS-H and its wild-type parent strain revealed comparatively lower levels of Obg in MS-H. These results indicate that not only the mutation in Obg, but also the level of Obg expression, can confer functional abnormalities in the bacterial host. Furthermore, with the construction of first expression vector for M. synoviae, this study has set foundation for the development of recombinant vaccine(s) based on MS-H.

Genetic variation in Mycobacterium tuberculosis isolates from a London outbreak associated with isoniazid resistance

BACKGROUND

The largest outbreak of isoniazid-resistant (INH-R) Mycobacterium tuberculosis in Western Europe is centred in North London, with over 400 cases diagnosed since 1995. In the current study, we evaluated the genetic variation in a subset of clinical samples from the outbreak with the hypothesis that these isolates have unique biological characteristics that have served to prolong the outbreak.

METHODS

Fitness assays, mutation rate estimation, and whole-genome sequencing were performed to test for selective advantage and compensatory mutations.

RESULTS

This detailed analysis of the genetic variation of these INH-R samples suggests that this outbreak consists of successful, closely related, circulating strains with heterogeneous resistance profiles and little or no associated fitness cost or impact on their mutation rate.

CONCLUSIONS

Specific deletions and SNPs could be a peculiar feature of these INH-R M. tuberculosis isolates, and could potentially explain their persistence over the years.

Whole genome sequencing of bacteria in cystic fibrosis as a model for bacterial genome adaptation and evolution

Cystic fibrosis (CF) airways harbor a wide variety of new and/or emerging multidrug resistant bacteria which impose a heavy burden on patients. These bacteria live in close proximity with one another, which increases the frequency of lateral gene transfer. The exchange and movement of mobile genetic elements and genomic islands facilitate the spread of genes between genetically diverse bacteria, which seem to be advantageous to the bacterium as it allows adaptation to the new niches of the CF lungs. Niche adaptation is one of the major evolutionary forces shaping bacterial genome composition and in CF the chronic strains adapt and become less virulent. The purpose of this review is to shed light on CF bacterial genome alterations. Next-generation sequencing technology is an exciting tool that may help us to decipher the genome architecture and the evolution of bacteria colonizing CF lungs.

MTCID: a database of genetic polymorphisms in clinical isolates of Mycobacterium tuberculosis

Tuberculosis (TB) is a major cause of morbidity and mortality throughout the world, particularly in developing countries. The response of the patients and treatment outcome depends, in addition to diagnosis, appropriate and timely treatment and host factors, on the virulence of Mycobacterium tuberculosis and genetic polymorphism prevalent in clinical isolates of the bacterium. A number of studies have been carried out to characterize clinical isolates of M. tuberculosis obtained from TB patients. However, the data is scattered in a large number of publications. Though attempts have been made to catalog the observed variations, there is no database that has been developed for cataloging, storing and dissemination of genetic polymorphism information. MTCID (M. tuberculosis clinical isolate genetic polymorphism database) is an attempt to provide a comprehensive repository to store, access and disseminate single nucleotide polymorphism (SNPs) and spoligotyping profiles of M. tuberculosis. It can be used to automatically upload the information available with a user that adds to the existing database at the backend. Besides it may also aid in maintaining clinical profiles of TB and treatment of patients. The database has 'search' features and is available at http://ccbb.jnu.ac.in/Tb.

Horizontal gene transfer in Histophilus somni and its role in the evolution of pathogenic strain 2336, as determined by comparative genomic analyses

BACKGROUND

Pneumonia and myocarditis are the most commonly reported diseases due to Histophilus somni, an opportunistic pathogen of the reproductive and respiratory tracts of cattle. Thus far only a few genes involved in metabolic and virulence functions have been identified and characterized in H. somni using traditional methods. Analyses of the genome sequences of several Pasteurellaceae species have provided insights into their biology and evolution. In view of the economic and ecological importance of H. somni, the genome sequence of pneumonia strain 2336 has been determined and compared to that of commensal strain 129Pt and other members of the Pasteurellaceae.

RESULTS

The chromosome of strain 2336 (2,263,857 bp) contained 1,980 protein coding genes, whereas the chromosome of strain 129Pt (2,007,700 bp) contained only 1,792 protein coding genes. Although the chromosomes of the two strains differ in size, their average GC content, gene density (total number of genes predicted on the chromosome), and percentage of sequence (number of genes) that encodes proteins were similar. The chromosomes of these strains also contained a number of discrete prophage regions and genomic islands. One of the genomic islands in strain 2336 contained genes putatively involved in copper, zinc, and tetracycline resistance. Using the genome sequence data and comparative analyses with other members of the Pasteurellaceae, several H. somni genes that may encode proteins involved in virulence (e.g., filamentous haemaggutinins, adhesins, and polysaccharide biosynthesis/modification enzymes) were identified. The two strains contained a total of 17 ORFs that encode putative glycosyltransferases and some of these ORFs had characteristic simple sequence repeats within them. Most of the genes/loci common to both the strains were located in different regions of the two chromosomes and occurred in opposite orientations, indicating genome rearrangement since their divergence from a common ancestor.

CONCLUSIONS

Since the genome of strain 129Pt was ~256,000 bp smaller than that of strain 2336, these genomes provide yet another paradigm for studying evolutionary gene loss and/or gain in regard to virulence repertoire and pathogenic ability. Analyses of the complete genome sequences revealed that bacteriophage- and transposon-mediated horizontal gene transfer had occurred at several loci in the chromosomes of strains 2336 and 129Pt. It appears that these mobile genetic elements have played a major role in creating genomic diversity and phenotypic variability among the two H. somni strains.

Epidemiology and virulence insights from MRSA and MSSA genome analysis

Staphylococcus aureus is a major human pathogen responsible for a wide diversity of infections ranging from localized to life threatening diseases. From 1961 and the emergence of methicillin-resistant S. aureus (MRSA), this bacterium has shown a particular capacity to survive and adapt to drastic environmental changes and since the beginning of the 1990s it has spread worldwide. Until recently, S. aureus was considered as the prototype of a nosocomial pathogen but it has now been recognized as an agent responsible for outbreaks in the community. Several recent reports suggest that the epidemiology of MRSA is changing. Understanding of pathogenicity, virulence and emergence of epidemic clones within MRSA populations is not clearly defined, despite several attempts to identify common molecular features between strains that share similar epidemiological and/or virulence behavior. These studies included: pattern profiling of bacterial adhesins, analysis of clonal complex groups, molecular genotyping and enterotoxin content analysis. To date, all approaches failed to find a correlation between molecular determinants and clinical outcomes. We hypothesize that the capacity of the bacterium to become more invasive or virulent is determined by genetics. The utilization of massively parallel methods of analysis is therefore ideal to study the contribution of genetics. Therefore, this article focuses on the entire genome including coding sequences as well as noncoding sequences. This high resolution approach allows the monitoring micro- and macroevolution of MRSA and identification of specific genomic markers of evolution of invasive or highly virulent phenotypes.

New approaches for functional genomic studies in staphylococci

Functional transcriptomics studies have resulted in interesting insights into Staphylococcus aureus diversity and pathogenicity. Here we review the principles, advantages and disadvantages of recent technical developments in the field of transcriptomics and their potential impact on S. aureus research.

Metagenomic study of the oral microbiota by Illumina high-throughput sequencing

To date, metagenomic studies have relied on the utilization and analysis of reads obtained using 454 pyrosequencing to replace conventional Sanger sequencing. After extensively scanning the 16S ribosomal RNA (rRNA) gene, we identified the V5 hypervariable region as a short region providing reliable identification of bacterial sequences available in public databases such as the Human Oral Microbiome Database. We amplified samples from the oral cavity of three healthy individuals using primers covering an approximately 82-base segment of the V5 loop, and sequenced using the Illumina technology in a single orientation. We identified 135 genera or higher taxonomic ranks from the resulting 1,373,824 sequences. While the abundances of the most common phyla (Firmicutes, Proteobacteria, Actinobacteria, Fusobacteria and TM7) are largely comparable to previous studies, Bacteroidetes were less present. Potential sources for this difference include classification bias in this region of the 16S rRNA gene, human sample variation, sample preparation and primer bias. Using an Illumina sequencing approach, we achieved a much greater depth of coverage than previous oral microbiota studies, allowing us to identify several taxa not yet discovered in these types of samples, and to assess that at least 30,000 additional reads would be required to identify only one additional phylotype. The evolution of high-throughput sequencing technologies, and their subsequent improvements in read length enable the utilization of different platforms for studying communities of complex flora. Access to large amounts of data is already leading to a better representation of sample diversity at a reasonable cost.

A hybrid computational grid architecture for comparative genomics

Comparative genomics provides a powerful tool for studying evolutionary changes among organisms, helping to identify genes that are conserved among species, as well as genes that give each organism its unique characteristics. However, the huge datasets involved makes this approach impractical on traditional computer architectures leading to prohibitively long runtimes. In this paper, we present a new computational grid architecture based on a hybrid computing model to significantly accelerate comparative genomics applications. The hybrid computing model consists of two types of parallelism: coarse grained and fine grained. The coarse-grained parallelism uses a volunteer computing infrastructure for job distribution, while the fine-grained parallelism uses commodity computer graphics hardware for fast sequence alignment. We present the deployment and evaluation of this approach on our grid test bed for the all-against-all comparison of microbial genomes. The results of this comparison are then used by phenotype--genotype explorer (PheGee). PheGee is a new tool that nominates candidate genes responsible for a given phenotype.

Leishmania and the leishmaniases: a parasite genetic update and advances in taxonomy, epidemiology and pathogenicity in humans

Leishmaniases remain a major public health problem today despite the vast amount of research conducted on Leishmania pathogens. The biological model is genetically and ecologically complex. This paper explores the advances in Leishmania genetics and reviews population structure, taxonomy, epidemiology and pathogenicity. Current knowledge of Leishmania genetics is placed in the context of natural populations. Various studies have described a clonal structure for Leishmania but recombination, pseudo-recombination and other genetic processes have also been reported. The impact of these different models on epidemiology and the medical aspects of leishmaniases is considered from an evolutionary point of view. The role of these parasites in the expression of pathogenicity in humans is also explored. It is important to ascertain whether genetic variability of the parasites is related to the different clinical expressions of leishmaniasis. The review aims to put current knowledge of Leishmania and the leishmaniases in perspective and to underline priority questions which 'leishmaniacs' must answer in various domains: epidemiology, population genetics, taxonomy and pathogenicity. It concludes by presenting a number of feasible ways of responding to these questions.

Identification of genetic differences between two clinical isolates of Streptococcus mutans by suppression subtractive hybridization

Streptococcus mutans is generally considered to be the principal aetiological agent for dental caries. Phenotypic variation in strains is often associated with differences in gene content, so the isolation of DNA fragments from these genes or associated regions is illuminating. The S. mutans strains 9-1 and 9-2, which both colonized the same oral cavity, were selected after screening for the possession of suspected virulence traits. Genomic DNA of strain 9-1 was used as the tester, and that of 9-2 was used as the driver. Suppression subtractive hybridization (SSH) was applied between the tester and the driver DNAs. The subtractive products were cloned into a pCR2.1 vector. Clone libraries representing sequence differences were obtained. The subtractive fragments that were found specifically in strain 9-1 but not in strain 9-2 were identified by dot blotting and then sequenced. BLASTn and BLASTx sequence homology analyses were subsequently performed. Twenty-seven sequences were found in the genome of strain 9-1 that were not in 9-2. Among them, three revealed no homology to published nucleotide sequences while the remaining sequences showed 81-100% homology to known genes of S. mutans strain UA159. These sequences are involved in competence development, signal transduction and transcriptional regulation, repairing stress damage, transport, carbohydrate catabolism, biochemical synthesis, or unknown functions. Differences exist in the genomes of different S. mutans isolates. SSH is effective in screening for S. mutans strain specific DNA sequences.

The impact of comparative genomics on infectious disease research

The past decade has witnessed a revolution in infectious disease research, fuelled by the accumulation of a huge amount of DNA sequence data. The avalanche of genome sequence information has largely promoted the development of comparative genomics, which exploits available genome sequences to perform either inter- or intra-species comparisons of bacterial genome contents, or performs comparisons between the human genome and those of other organisms. This review aims to summarize how comparative genomics is being extensively used in infectious disease research, such as in the studies to identify virulence determinants, antimicrobial drug targets, vaccine candidates and new markers for diagnostics. These applications hold considerable promise for alleviating the burden of infectious diseases in the coming years.

The evolution of IncP catabolic plasmids

The recent adoption of whole plasmid genome sequencing as a routine analytical technique has provided the basis for cataloging the historical events through which plasmids are assembled from the available families of modular plasmid components. Horizontal gene transfer mediated by plasmids plays an important role in the adaptation of bacteria to the presence of specific metabolizable compounds, including man-made chemicals, in the surrounding environment. Bacterial plasmid genome sequence comparisons indicate that plasmids have complex genetic histories resulting from transposition, homologous recombination, and illegitimate recombinational events. Evidence from IncP plasmid genome sequences indicates that cryptic plasmid backbones acquire diverse catabolic pathways through gene capture and horizontal gene transfer.

Postgenomic taxonomy of human ureaplasmas -- a case study based on multiple gene sequences

In 2000, the full genome sequence of Ureaplasma parvum (previously known as Ureaplasma urealyticum) serovar 3 was released. In 2002, after prolonged debate, it was agreed that the former U. urealyticum should be divided into two species -- U. parvum and U. urealyticum. To provide additional support for this decision and improve our understanding of the relationship between these two species, the authors studied four 'core' genes or gene clusters in ATCC reference strains of all 14 serovars of U. parvum and U. urealyticum. These 'core' regions were the rRNA gene clusters, the EF-Tu genes (tuf), urease gene clusters and multiple-banded antigen genes (mba). The known U. parvum genome sequences (GenBank accession no. NC_002162) were used as reference. DNA insertions and deletions (indels) were found in all of the gene regions studied, except tuf, but they were found only between, not within, the two species. An incidental finding was that there was inter-copy heterogeneity for rRNA gene cluster sequences. Sequence analysis (sequence heterogeneity and especially indels) of all four selected targets consistently supported the separation of human ureaplasmas into two species. Except for multiple-banded antigen, there was less heterogeneity in amino acid sequences of proteins, between species, than in the nucleic acid sequences of the corresponding genes. The degrees of heterogeneity at the 5' end of the species-specific regions of multiple-banded antigen were almost identical for both amino acid and nucleotide sequences. Analysis of the authors' results provided an interesting case study to help resolve some common problems in the use of sequence data to infer phylogenetic relationships and support taxonomic changes. It is recommended that, to avoid confusion, the new nomenclature be used for human ureaplasmas in future publications.

Genomic analysis distinguishes Mycobacterium africanum

Mycobacterium africanum is thought to comprise a unique species within the Mycobacterium tuberculosis complex. M. africanum has traditionally been identified by phenotypic criteria, occupying an intermediate position between M. tuberculosis and M. bovis according to biochemical characteristics. Although M. africanum isolates present near-identical sequence homology to other species of the M. tuberculosis complex, several studies have uncovered large genomic regions variably deleted from certain M. africanum isolates. To further investigate the genomic characteristics of organisms characterized as M. africanum, the DNA content of 12 isolates was interrogated by using Affymetrix GeneChip. Analysis revealed genomic regions of M. tuberculosis deleted from all isolates of putative diagnostic and biological consequence. The distribution of deleted sequences suggests that M. africanum subtype II isolates are situated among strains of "modern" M. tuberculosis. In contrast, other M. africanum isolates (subtype I) constitute two distinct evolutionary branches within the M. tuberculosis complex. To test for an association between deleted sequences and biochemical attributes used for speciation, a phenotypically diverse panel of "M. africanum-like" isolates from Guinea-Bissau was tested for these deletions. These isolates clustered together within one of the M. africanum subtype I branches, irrespective of phenotype. These results indicate that convergent biochemical profiles can be independently obtained for M. tuberculosis complex members, challenging the traditional approach to M. tuberculosis complex speciation. Furthermore, the genomic results suggest a rational framework for defining M. africanum and provide tools to accurately assess its prevalence in clinical specimens.

Genomic interrogation of the dassie bacillus reveals it as a unique RD1 mutant within the Mycobacterium tuberculosis complex

Despite their remarkable genetic homology, members of the Mycobacterium tuberculosis complex express very different phenotypes, most notably in their spectra of clinical presentation. For example, M. tuberculosis is regarded as pathogenic to humans, whereas members having deleted RD1, such as Mycobacterium microti and Mycobacterium bovis BCG, are not. The dassie bacillus, an infrequent variant of the M. tuberculosis complex characterized as being most similar to M. microti, is the causative agent of tuberculosis (TB) in the dassie (Procavia capensis). Intriguingly, the dassie bacillus is not pathogenic to rabbits or guinea pigs and has never been documented to infect humans. Although it was identified more than a half-century ago, the reasons behind its attenuation are unknown. Because large sequence polymorphisms have presented themselves as the most obvious genomic distinction among members of the M. tuberculosis complex, the DNA content of the dassie bacillus was interrogated by Affymetrix GeneChip to identify regions that are absent from it but present in M. tuberculosis H37Rv. Comparison has led to the identification of nine regions of difference (RD), five of which are shared with M. microti (RDs 3, 7, 8, 9, and 10). Although the dassie bacillus does not share the other documented deletions in M. microti (RD1(mic), RD5(mic), MID1, MID2, and MID3), it has endured unique deletions in the regions of RD1, RD5, N-RD25, and Rv3081-Rv3082c (virS). RD1(das), affecting only Rv3874-Rv3877, is the smallest natural deletion of the RD1 region uncovered and points to genes within this region that are likely implicated in virulence. Newfound deletions from the dassie bacillus are discussed in relation to their evolutionary and biological significance.

Exploiting genomics, genetics and chemistry to combat antibiotic resistance

To address the worsening problem of antibiotic-resistant bacteria there is an urgent need to develop new antibiotics. Comparative genomics and molecular genetics are being applied to produce lists of essential new targets for compound screening programmes. Combinatorial chemistry and structural biology are being applied to rapidly explore and optimize the interactions between lead compounds and their biological targets. Several compounds that have been identified from target-based screens are now in development, but technical and economic constraints might result in a trickle, rather than a flood, of new antibiotics onto the market in the near future.

Genomic islands and the evolution of catabolic pathways in bacteria

Genes for the degradation of organic pollutants have usually been allocated to plasmid DNAs in bacteria or considered non-mobile when detected in the chromosome. New discoveries have shown that catabolic genes can also be part of so-called integrative and conjugative elements (ICElands), a group of mobile DNA elements also known as genomic islands and conjugative transposons. One such ICEland is the clc element for chlorobenzoate and chlorocatechol degradation in Pseudomonas sp. strain B13. Genome comparisons and genetic data on integrase functioning reveal that the clc element and several other unclassified ICElands belong to a group of elements with conserved features. The clc element is unique among them in carrying the genetic information for several degradation pathways, whereas the others give evidence for pathogenicity functions. Many more such elements may exist, bridging the gap between pathogenicity and degradation functions.

Comparative genomics in the fight against tuberculosis: diagnostics, epidemiology, and BCG vaccination

Although the causative agent of tuberculosis, Mycobacterium tuberculosis, has been known for some 120 years, the disease continues to plague humanity. In 1998, the sequencing of M. tuberculosis H37Rv enabled tuberculosis researchers to draw comparisons between it and other species of the closely-related M. tuberculosis complex, including bacillus Calmette-Guerin (BCG), the vaccine administered to prevent human tuberculosis. These efforts have uncovered genomic variability that potentially encodes the discrepant phenotypes displayed by species. Due to the infrequency of single nucleotide polymorphisms (SNPs) and other modes of genomic change, large sequence polymorphisms (LSPs) have presented themselves as the most obvious form of genomic variability among species. This review discusses genomic polymorphism among species of the M. tuberculosis complex as revealed through comparative genomics. Attention is drawn towards the impact of comparative genomics in generating several exciting hypotheses towards diagnosis, epidemiology, and prevention of tuberculosis disease.

Metabolic engineering of Lactococcus lactis: the impact of genomics and metabolic modelling

Lactic acid bacteria display a relatively simple and well described metabolism where the sugar source is converted mainly to lactic acid. Here we will shortly describe metabolic engineering strategies that led to the efficient re-routing of the lactococcal pyruvate metabolism to end-products other than lactic acid, including diacetyl and alanine. Moreover, we will review current metabolic engineering approaches that aim at increasing the flux through complex biosynthetic pathways, leading to exopolysaccharides and folic acid. Finally, the (future) impact of the developments in the area of genomics and corresponding high-throughput technologies will be discussed.

Genomic evidence that the intracellular proteins of archaeal microbes contain disulfide bonds

Disulfide bonds have only rarely been found in intracellular proteins. That pattern is consistent with the chemically reducing environment inside the cells of well-studied organisms. However, recent experiments and new calculations based on genomic data of archaea provide striking contradictions to this pattern. Our results indicate that the intracellular proteins of certain hyperthermophilic archaea, especially the crenarchaea Pyrobaculum aerophilum and Aeropyrum pernix, are rich in disulfide bonds. This finding implicates disulfide bonding in stabilizing many thermostable proteins and points to novel chemical environments inside these microbes. These unexpected results illustrate the wealth of biochemical insights available from the growing reservoir of genomic data.

Complete genomic sequence of Pasteurella multocida, Pm70

We present here the complete genome sequence of a common avian clone of Pasteurella multocida, Pm70. The genome of Pm70 is a single circular chromosome 2,257,487 base pairs in length and contains 2,014 predicted coding regions, 6 ribosomal RNA operons, and 57 tRNAs. Genome-scale evolutionary analyses based on pairwise comparisons of 1,197 orthologous sequences between P. multocida, Haemophilus influenzae, and Escherichia coli suggest that P. multocida and H. influenzae diverged approximately 270 million years ago and the gamma subdivision of the proteobacteria radiated about 680 million years ago. Two previously undescribed open reading frames, accounting for approximately 1% of the genome, encode large proteins with homology to the virulence-associated filamentous hemagglutinin of Bordetella pertussis. Consistent with the critical role of iron in the survival of many microbial pathogens, in silico and whole-genome microarray analyses identified more than 50 Pm70 genes with a potential role in iron acquisition and metabolism. Overall, the complete genomic sequence and preliminary functional analyses provide a foundation for future research into the mechanisms of pathogenesis and host specificity of this important multispecies pathogen.

The complexity of simplicity

What is the minimum number of genes or functions necessary to support cellular life? The concept of a 'minimal genome' has become popular, but is it a useful concept, and if so, what might a minimal genome encode? We argue that the concept may be useful, even though the goal of defining a general minimal genome may never be attained.