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1.  Cluster M Mycobacteriophages Bongo, PegLeg, and Rey with Unusually Large Repertoires of tRNA Isotypes 
Journal of Virology  2014;88(5):2461-2480.
Genomic analysis of a large set of phages infecting the common host Mycobacterium smegmatis mc2155 shows that they span considerable genetic diversity. There are more than 20 distinct types that lack nucleotide similarity with each other, and there is considerable diversity within most of the groups. Three newly isolated temperate mycobacteriophages, Bongo, PegLeg, and Rey, constitute a new group (cluster M), with the closely related phages Bongo and PegLeg forming subcluster M1 and the more distantly related Rey forming subcluster M2. The cluster M mycobacteriophages have siphoviral morphologies with unusually long tails, are homoimmune, and have larger than average genomes (80.2 to 83.7 kbp). They exhibit a variety of features not previously described in other mycobacteriophages, including noncanonical genome architectures and several unusual sets of conserved repeated sequences suggesting novel regulatory systems for both transcription and translation. In addition to containing transfer-messenger RNA and RtcB-like RNA ligase genes, their genomes encode 21 to 24 tRNA genes encompassing complete or nearly complete sets of isotypes. We predict that these tRNAs are used in late lytic growth, likely compensating for the degradation or inadequacy of host tRNAs. They may represent a complete set of tRNAs necessary for late lytic growth, especially when taken together with the apparent lack of codons in the same late genes that correspond to tRNAs that the genomes of the phages do not obviously encode.
IMPORTANCE The bacteriophage population is vast, dynamic, and old and plays a central role in bacterial pathogenicity. We know surprisingly little about the genetic diversity of the phage population, although metagenomic and phage genome sequencing indicates that it is great. Probing the depth of genetic diversity of phages of a common host, Mycobacterium smegmatis, provides a higher resolution of the phage population and how it has evolved. Three new phages constituting a new cluster M further expand the diversity of the mycobacteriophages and introduce novel features. As such, they provide insights into phage genome architecture, virion structure, and gene regulation at the transcriptional and translational levels.
PMCID: PMC3958112  PMID: 24335314
2.  Genome Sequence of Salmonella enterica subsp. enterica Strain Durban 
Genome Announcements  2014;2(3):e00399-14.
We report the genome sequence of Salmonella enterica subsp. enterica strain Durban, isolated from a patient with salmonellosis and typhoid fever. The strain is closely related to S. enterica subsp. enterica strain P125109 but differs in loss of the ϕSE20 prophage and acquisition of a prophage similar to ELPhiS.
PMCID: PMC4014692  PMID: 24812224
3.  Mycobacteriophages: Windows into Tuberculosis 
PLoS Pathogens  2014;10(3):e1003953.
PMCID: PMC3961340  PMID: 24651299
4.  Generation of Affinity-Tagged Fluoromycobacteriophages by Mixed Assembly of Phage Capsids 
Applied and Environmental Microbiology  2013;79(18):5608-5615.
Addition of affinity tags to bacteriophage particles facilitates a variety of applications, including vaccine construction and diagnosis of bacterial infections. Addition of tags to phage capsids is desirable, as modification of the tails can lead to poor adsorption and loss of infectivity. Although tags can readily be included as fusions to head decoration proteins, many phages do not have decoration proteins as virion components. The addition of a small (10-amino-acid) Strep-tag II (STAG II) to the mycobacteriophage TM4 capsid subunit, gp9, was not tolerated as a genetically homogenous recombinant phage but could be incorporated into the head by growth of wild-type phage on a host expressing the capsid-STAG fusion. Particles with capsids composed of wild-type and STAG-tagged subunit mixtures could be grown to high titers, showed good infectivities, and could be used to isolate phage-bacterium complexes. Preparation of a STAG-labeled fluoromycobacteriophage enabled capture of bacterial complexes and identification of infected bacteria by fluorescence.
PMCID: PMC3754161  PMID: 23851082
5.  A Broadly Implementable Research Course in Phage Discovery and Genomics for First-Year Undergraduate Students 
mBio  2014;5(1):e01051-13.
Engaging large numbers of undergraduates in authentic scientific discovery is desirable but difficult to achieve. We have developed a general model in which faculty and teaching assistants from diverse academic institutions are trained to teach a research course for first-year undergraduate students focused on bacteriophage discovery and genomics. The course is situated within a broader scientific context aimed at understanding viral diversity, such that faculty and students are collaborators with established researchers in the field. The Howard Hughes Medical Institute (HHMI) Science Education Alliance Phage Hunters Advancing Genomics and Evolutionary Science (SEA-PHAGES) course has been widely implemented and has been taken by over 4,800 students at 73 institutions. We show here that this alliance-sourced model not only substantially advances the field of phage genomics but also stimulates students’ interest in science, positively influences academic achievement, and enhances persistence in science, technology, engineering, and mathematics (STEM) disciplines. Broad application of this model by integrating other research areas with large numbers of early-career undergraduate students has the potential to be transformative in science education and research training.
Engagement of undergraduate students in scientific research at early stages in their careers presents an opportunity to excite students about science, technology, engineering, and mathematics (STEM) disciplines and promote continued interests in these areas. Many excellent course-based undergraduate research experiences have been developed, but scaling these to a broader impact with larger numbers of students is challenging. The Howard Hughes Medical Institute (HHMI) Science Education Alliance Phage Hunting Advancing Genomics and Evolutionary Science (SEA-PHAGES) program takes advantage of the huge size and diversity of the bacteriophage population to engage students in discovery of new viruses, genome annotation, and comparative genomics, with strong impacts on bacteriophage research, increased persistence in STEM fields, and student self-identification with learning gains, motivation, attitude, and career aspirations.
PMCID: PMC3950523  PMID: 24496795
6.  Complete Genome Sequences of 63 Mycobacteriophages 
Genome Announcements  2013;1(6):e00847-13.
Mycobacteriophages are viruses that infect mycobacterial hosts. The current collection of sequenced mycobacteriophages—all isolated on a single host strain, Mycobacterium smegmatis mc2155, reveals substantial genetic diversity. The complete genome sequences of 63 newly isolated mycobacteriophages expand the resolution of our understanding of phage diversity.
PMCID: PMC3869317  PMID: 24285655
7.  Evolution of genetic switch complexity 
Bacteriophage  2013;3(1):e24186.
The circuitry of the phage λ genetic switch determining the outcome of lytic or lysogenic growth is well-integrated and complex, raising the question as to how it evolved. It is plausible that it arose from a simpler ancestral switch with fewer components that underwent various additions and refinements, as it adapted to vast numbers of different hosts and conditions. We have recently identified a new class of genetic switches found in mycobacteriophages and other prophages, in which immunity is dependent on integration. These switches contain only three genes (integrase, repressor and cro) and represent a major departure from the λ-like circuitry, lacking many features such as xis, cII and cIII. These small self-contained switches represent an unrealized, elegant circuitry for controlling infection outcome. In this addendum, we propose a model of possible events in the evolution of a complex λ-like switch from a simpler integration-dependent switch.
PMCID: PMC3694055  PMID: 23819104
genetic switch; genetic circuits; bistable; integration-dependent immunity; lytic and lysogenic growth
8.  Mycobacteriophage Marvin: a New Singleton Phage with an Unusual Genome Organization 
Journal of Virology  2012;86(9):4762-4775.
Mycobacteriophages represent a genetically diverse group of viruses that infect mycobacterial hosts. Although more than 80 genomes have been sequenced, these still poorly represent the likely diversity of the broader population of phages that can infect the host, Mycobacterium smegmatis mc2155. We describe here a newly discovered phage, Marvin, which is a singleton phage, having no previously identified close relatives. The 65,100-bp genome contains 107 predicted protein-coding genes arranged in a noncanonical genomic architecture in which a subset of the minor tail protein genes are displaced about 20 kbp from their typical location, situated among nonstructural genes anticipated to be expressed early in lytic growth. Marvin is not temperate, and stable lysogens cannot be recovered from infections, although the presence of a putative xis gene suggests that Marvin could be a relatively recent derivative of a temperate parent. The Marvin genome is replete with novel genes not present in other mycobacteriophage genomes, and although most are of unknown function, the presence of amidoligase and glutamine amidotransferase genes suggests intriguing possibilities for the interactions of Marvin with its mycobacterial hosts.
PMCID: PMC3347389  PMID: 22357284
9.  Propionibacterium acnes Bacteriophages Display Limited Genetic Diversity and Broad Killing Activity against Bacterial Skin Isolates 
mBio  2012;3(5):e00279-12.
Investigation of the human microbiome has revealed diverse and complex microbial communities at distinct anatomic sites. The microbiome of the human sebaceous follicle provides a tractable model in which to study its dominant bacterial inhabitant, Propionibacterium acnes, which is thought to contribute to the pathogenesis of the human disease acne. To explore the diversity of the bacteriophages that infect P. acnes, 11 P. acnes phages were isolated from the sebaceous follicles of donors with healthy skin or acne and their genomes were sequenced. Comparative genomic analysis of the P. acnes phage population, which spans a 30-year temporal period and a broad geographic range, reveals striking similarity in terms of genome length, percent GC content, nucleotide identity (>85%), and gene content. This was unexpected, given the far-ranging diversity observed in virtually all other phage populations. Although the P. acnes phages display a broad host range against clinical isolates of P. acnes, two bacterial isolates were resistant to many of these phages. Moreover, the patterns of phage resistance correlate closely with the presence of clustered regularly interspaced short palindromic repeat elements in the bacteria that target a specific subset of phages, conferring a system of prokaryotic innate immunity. The limited diversity of the P. acnes bacteriophages, which may relate to the unique evolutionary constraints imposed by the lipid-rich anaerobic environment in which their bacterial hosts reside, points to the potential utility of phage-based antimicrobial therapy for acne.
Propionibacterium acnes is a dominant member of the skin microflora and has also been implicated in the pathogenesis of acne; however, little is known about the bacteriophages that coexist with and infect this bacterium. Here we present the novel genome sequences of 11 P. acnes phages, thereby substantially increasing the amount of available genomic information for this phage population. Surprisingly, we find that, unlike other well-studied bacteriophages, P. acnes phages are highly homogeneous and show a striking lack of genetic diversity, which is perhaps related to their unique and restricted habitat. They also share a broad ability to kill clinical isolates of P. acnes; phage resistance is not prevalent, but when detected, it appears to be conferred by chromosomally encoded immunity elements within the host genome. We believe that these phages display numerous features that would make them ideal candidates for the development of a phage-based therapy for acne.
PMCID: PMC3448167  PMID: 23015740
10.  Complete Genome Sequences of 138 Mycobacteriophages 
Journal of Virology  2012;86(4):2382-2384.
Bacteriophages are the most numerous biological entities in the biosphere, and although their genetic diversity is high, it remains ill defined. Mycobacteriophages—the viruses of mycobacterial hosts—provide insights into this diversity as well as tools for manipulating Mycobacterium tuberculosis. We report here the complete genome sequences of 138 new mycobacteriophages, which—together with the 83 mycobacteriophages previously reported—represent the largest collection of phages known to infect a single common host, Mycobacterium smegmatis mc2 155.
PMCID: PMC3302410  PMID: 22282335
11.  Mycobacteriophages BPs, Angel and Halo: comparative genomics reveals a novel class of ultra-small mobile genetic elements 
Microbiology  2009;155(Pt 9):2962-2977.
Mycobacteriophages BPs, Angel and Halo are closely related viruses isolated from Mycobacterium smegmatis, and possess the smallest known mycobacteriophage genomes, 41 901 bp, 42 289 bp and 41 441 bp, respectively. Comparative genome analysis reveals a novel class of ultra-small mobile genetic elements; BPs and Halo each contain an insertion of the proposed mobile elements MPME1 and MPME2, respectively, at different locations, while Angel contains neither. The close similarity of the genomes provides a comparison of the pre- and post-integration sequences, revealing an unusual 6 bp insertion at one end of the element and no target duplication. Nine additional copies of these mobile elements are identified in a variety of different contexts in other mycobacteriophage genomes. In addition, BPs, Angel and Halo have an unusual lysogeny module in which the repressor and integrase genes are closely linked. The attP site is located within the repressor-coding region, such that prophage formation results in expression of a C-terminally truncated, but active, form of the repressor.
PMCID: PMC2833263  PMID: 19556295
12.  Mycobacteriophages BPs, Angel and Halo: comparative genomics reveals a novel class of ultra-small mobile genetic elements 
Microbiology (Reading, England)  2009;155(Pt 9):2962-2977.
Mycobacteriophages BPs, Angel and Halo are closely related viruses isolated from Mycobacterium smegmatis, and possess the smallest known mycobacteriophage genomes, 41 901 bp, 42 289 bp and 41 441 bp, respectively. Comparative genome analysis reveals a novel class of ultra-small mobile genetic elements; BPs and Halo each contain an insertion of the proposed mobile elements MPME1 and MPME2, respectively, at different locations, while Angel contains neither. The close similarity of the genomes provides a comparison of the pre- and post-integration sequences, revealing an unusual 6 bp insertion at one end of the element and no target duplication. Nine additional copies of these mobile elements are identified in a variety of different contexts in other mycobacteriophage genomes. In addition, BPs, Angel and Halo have an unusual lysogeny module in which the repressor and integrase genes are closely linked. The attP site is located within the repressor-coding region, such that prophage formation results in expression of a C-terminally truncated, but active, form of the repressor.
PMCID: PMC2833263  PMID: 19556295
13.  The Structure of Xis reveals the basis for Filament Formation and insight into DNA bending within a mycobacteriophage Intasome 
Journal of molecular biology  2013;426(2):412-422.
The Recombination Directionality Factor, Xis, is a DNA bending protein that determines the outcome of integrase-mediated site-specific recombination by redesign of higher-order protein-DNA architectures. Although the attachment site DNA of Mycobacteriophage Pukovnik is likely to contain four sites for Xis binding, Xis crystals contain five subunits in the asymmetric unit, four of which align into a Xis filament, and a fifth that is generated by an unusual domain swap. Extensive intersubunit contacts stabilize a bent filament-like arrangement with Xis monomers aligned head-to-tail. The structure implies a DNA bend of ~120°, which is in agreement with DNA bending measured in vitro. Formation of attR-containing intasomes requires only Int and Xis, distinguishing Pukovnik from lambda. Therefore, we conclude that in Pukovnik, Xis-induced DNA bending is sufficient to promote intramolecular Int-mediated bridges during intasome formation.
PMCID: PMC3902635  PMID: 24112940
DNA recombination; mycobacteriophage Pukovnik; Xis; DNA bending; filament; structure
14.  Cross-talk between diverse serine integrases 
Journal of molecular biology  2013;426(2):318-331.
Phage-encoded serine-integrases are large serine-recombinases that mediate integrative and excisive site-specific recombination of temperate phage genomes. They are well suited for use in heterologous systems and for synthetic genetic circuits as the attP and attB attachment sites are small (<50 bp), there are no host factor or DNA supercoiling requirements, and they are strongly directional, doing only excisive recombination in the presence of a recombination directionality factor. Combining different recombinases that function independently and without cross-talk to construct complex synthetic circuits is desirable, and several different serine-integrases are available. However, we show here that these functions are not reliably predictable, and we describe a pair of serine-integrases encoded by mycobacteriophages Bxz2 and Peaches with unusual and unpredictable specificities. The Integrases share only 59% amino acid sequence identity and the attP sites have fewer than 50% shared bases, but they use the same attB site and there is non-reciprocal cross-talk between the two systems. The DNA binding specificities do not result from differences in specific DNA contacts, but from the constraints imposed by the configuration of the component half-sites within each of the attachment site DNAs.
PMCID: PMC3947336  PMID: 24161951
15.  Comparative genomic analysis of mycobacteriophage Tweety: evolutionary insights and construction of compatible site-specific integration vectors for mycobacteria 
Microbiology  2007;153(Pt 8):2711-2723.
Mycobacteriophage Tweety is a newly isolated phage of Mycobacterium smegmatis. It has a viral morphology with an isometric head and a long flexible tail, and forms turbid plaques from which stable lysogens can be isolated. The Tweety genome is 58 692 bp in length, contains 109 protein-coding genes, and shows significant but interrupted nucleotide sequence similarity with the previously described mycobacteriophages Llij, PMC and Che8. However, overall the genome possesses mosaic architecture, with gene products being related to other mycobacteriophages such as Che9d, Omega and Corndog. A gene encoding an integrase of the tyrosine-recombinase family is located close to the centre of the genome, and a putative attP site has been identified within a short intergenic region immediately upstream of int. This Tweety attP–int cassette was used to construct a new set of integration-proficient plasmid vectors that efficiently transform both fast- and slow-growing mycobacteria through plasmid integration at a chromosomal locus containing a tRNALys gene. These vectors are maintained well in the absence of selection and are completely compatible with integration vectors derived from mycobacteriophage L5, enabling the simple construction of complex recombinants with genes integrated simultaneously at different chromosomal positions.
PMCID: PMC2884959  PMID: 17660435
16.  Molecular Genetics of Mycobacteriophages 
Microbiology spectrum  2014;2(2):1-36.
Mycobacteriophages have provided numerous essential tools for mycobacterial genetics, including delivery systems for transposons, reporter genes, and allelic exchange substrates, and components for plasmid vectors and mutagenesis. Their genetically diverse genomes also reveal insights into the broader nature of the phage population and the evolutionary mechanisms that give rise to it. The substantial advances in our understanding of the biology of mycobacteriophages including a large collection of completely sequenced genomes indicates a rich potential for further contributions in tuberculosis genetics and beyond.
PMCID: PMC4199240  PMID: 25328854
17.  Genome Sequence of Salmonella Phage 9NA 
Genome Announcements  2014;2(4):e00531-14.
The virulent double-stranded DNA (dsDNA) bacteriophage 9NA infects Salmonella enterica serovar Typhimurium and has a long noncontractile tail. We report its complete 52,869-bp genome sequence. Phage 9NA and two closely related S. enterica serovar Newport phages represent a tailed phage type whose molecular lifestyle has not yet been studied in detail.
PMCID: PMC4153490  PMID: 25146133
18.  Enhanced Specialized Transduction Using Recombineering in Mycobacterium tuberculosis 
mBio  2014;5(3):e01179-14.
Genetic engineering has contributed greatly to our understanding of Mycobacterium tuberculosis biology and has facilitated antimycobacterial and vaccine development. However, methods to generate M. tuberculosis deletion mutants remain labor-intensive and relatively inefficient. Here, methods are described that significantly enhance the efficiency (greater than 100-fold) of recovering deletion mutants by the expression of mycobacteriophage recombineering functions during the course of infection with specialized transducing phages delivering allelic exchange substrates. This system has been successfully applied to the CDC1551 strain of M. tuberculosis, as well as to a ΔrecD mutant generated in the CDC1551 parental strain. The latter studies were undertaken as there were precedents in both the Escherichia coli literature and mycobacterial literature for enhancement of homologous recombination in strains lacking RecD. In combination, these measures yielded a dramatic increase in the recovery of deletion mutants and are expected to facilitate construction of a comprehensive library of mutants with every nonessential gene of M. tuberculosis deleted. The findings also open up the potential for sophisticated genetic screens, such as synthetic lethal analyses, which have so far not been feasible for the slow-growing mycobacteria.
Genetic manipulation of M. tuberculosis is hampered by laborious and relatively inefficient methods for generating deletion mutant strains. The combined use of phage-based transduction and recombineering methods greatly enhances the efficiency by which knockout strains can be generated. The additional elimination of recD further enhances this efficiency. The methods described herein will facilitate the construction of comprehensive gene knockout libraries and expedite the isolation of previously difficult to recover mutants, promoting antimicrobial and vaccine development.
PMCID: PMC4045075  PMID: 24865558
19.  Evolutionary Relationships among Actinophages and a Putative Adaptation for Growth in Streptomyces spp. 
Journal of Bacteriology  2013;195(21):4924-4935.
The genome sequences of eight Streptomyces phages are presented, four of which were isolated for this study. Phages R4, TG1, ϕHau3, and SV1 were isolated previously and have been exploited as tools for understanding and genetically manipulating Streptomyces spp. We also extracted five apparently intact prophages from recent Streptomyces spp. genome projects and, together with six phage genomes in the database, we analyzed all 19 Streptomyces phage genomes with a view to understanding their relationships to each other and to other actinophages, particularly the mycobacteriophages. Fifteen of the Streptomyces phages group into four clusters of related genomes. Although the R4-like phages do not share nucleotide sequence similarity with other phages, they clearly have common ancestry with cluster A mycobacteriophages, sharing many protein homologues, common gene syntenies, and similar repressor-stoperator regulatory systems. The R4-like phage ϕHau3 and the prophage StrepC.1 (from Streptomyces sp. strain C) appear to have hijacked a unique adaptation of the streptomycetes, i.e., use of the rare UUA codon, to control translation of the essential phage protein, the terminase. The Streptomyces venezuelae generalized transducing phage SV1 was used to predict the presence of other generalized transducing phages for different Streptomyces species.
PMCID: PMC3807479  PMID: 23995638
20.  Functional requirements for bacteriophage growth: Gene essentiality and expression in Mycobacteriophage Giles 
Molecular microbiology  2013;88(3):577-589.
Bacteriophages represent a majority of all life forms, and the vast, dynamic population with early origins is reflected in their enormous genetic diversity. A large number of bacteriophage genomes have been sequenced. They are replete with novel genes without known relatives. We know little about their functions, which genes are required for lytic growth, and how they are expressed. Furthermore, the diversity is such that even genes with required functions – such as virion proteins and repressors – cannot always be recognized. Here we describe a functional genomic dissection of mycobacteriophage Giles, in which the virion proteins are identified, genes required for lytic growth are determined, the repressor is identified, and the transcription patterns determined. We find that although all of the predicted phage genes are expressed either in lysogeny or in lytic growth, 45% of the predicted genes are non-essential for lytic growth. We also describe genes required for DNA replication, show that recombination is required for lytic growth, and that Giles encodes a novel repressor. RNAseq analysis reveals abundant expression of a small non-coding RNA in a lysogen and in late lytic growth, although it is non-essential for lytic growth and does not alter lysogeny.
PMCID: PMC3641587  PMID: 23560716
Bacteriophage; Transcription; RNAseq
21.  Snapshot of haloarchaeal tailed virus genomes 
RNA Biology  2013;10(5):803-816.
The complete genome sequences of archaeal tailed viruses are currently highly underrepresented in sequence databases. Here, we report the genomic sequences of 10 new tailed viruses infecting different haloarchaeal hosts. Among these, only two viral genomes are closely related to each other and to previously described haloviruses HF1 and HF2. The approximately 760 kb of new genomic sequences in total shows no matches to CRISPR/Cas spacer sequences in haloarchaeal host genomes. Despite their high divergence, we were able to identify virion structural and assembly genes as well as genes coding for DNA and RNA metabolic functions. Interestingly, we identified many genes and genomic features that are shared with tailed bacteriophages, consistent with the hypothesis that haloarchaeal and bacterial tailed viruses share common ancestry, and that a viral lineage containing archaeal viruses, bacteriophages and eukaryotic viruses predates the division of the three major domains of non-viral life. However, as in tailed viruses in general and in haloarchaeal tailed viruses in particular, there are still a considerable number of predicted genes of unknown function.
PMCID: PMC3737338  PMID: 23470522
virus; haloarchaea; Archaea; tailed virus; bacteriophage; genome; sequence
22.  Integration-dependent bacteriophage immunity provides insights into the evolution of genetic switches 
Molecular cell  2012;49(2):237-248.
Genetic switches are critical components of developmental circuits. Because temperate bacteriophages are vastly abundant and greatly diverse, they are rich resources for understanding the mechanisms and evolution of switches and the molecular control of genetic circuitry. Here, we describe a new class of small, compact, and simple switches that use site-specific recombination as the key decision point. The phage attachment site attP is located within the phage repressor gene such that chromosomal integration results in removal of a C-terminal tag that destabilizes the virally-encoded form of the repressor. Integration thus not only confers prophage stability, but also is a requirement for lysogenic establishment. The variety of these self-contained integration-dependent immunity systems in different genomic contexts suggests that these represent ancestral states in switch evolution from which more complex switches have evolved. They also provide a powerful toolkit for building synthetic biological circuits.
PMCID: PMC3557535  PMID: 23246436
23.  On the nature of mycobacteriophage diversity and host preference 
Virology  2012;434(2):187-201.
The complete genome sequences of over 220 mycobacteriophages reveal them to be highly diverse, with numerous types sharing little or no nucleotide sequence identity with each other. We have determined the preferences of these phages for M. tuberculosis and for other strains of M. smegmatis, and find there is a correlation between genome type (cluster, subcluster, singleton) and host range. For many of the phages, expansion of host range occurs at relatively high frequencies, and we describe several examples in which host constraints occur at early stages of infection (adsorption or DNA injection), and phages have the ability to expand their host range through mutations in tail genes. We present a model in which phage diversity is a function of both the ability of phages to rapidly adapt to new hosts and the richness of the diversity of the bacterial population from which those phages are isolated.
PMCID: PMC3518647  PMID: 23084079
Bacteriophage; Mycobacteriophage; Host Range; Genome
24.  Cluster J Mycobacteriophages: Intron Splicing in Capsid and Tail Genes 
PLoS ONE  2013;8(7):e69273.
Bacteriophages isolated on Mycobacterium smegmatis mc2155 represent many distinct genomes sharing little or no DNA sequence similarity. The genomes are architecturally mosaic and are replete with genes of unknown function. A new group of genomes sharing substantial nucleotide sequences constitute Cluster J. The six mycobacteriophages forming Cluster J are morphologically members of the Siphoviridae, but have unusually long genomes ranging from 106.3 to 117 kbp. Reconstruction of the capsid by cryo-electron microscopy of mycobacteriophage BAKA reveals an icosahedral structure with a triangulation number of 13. All six phages are temperate and homoimmune, and prophage establishment involves integration into a tRNA-Leu gene not previously identified as a mycobacterial attB site for phage integration. The Cluster J genomes provide two examples of intron splicing within the virion structural genes, one in a major capsid subunit gene, and one in a tail gene. These genomes also contain numerous free-standing HNH homing endonuclease, and comparative analysis reveals how these could contribute to genome mosaicism. The unusual Cluster J genomes provide new insights into phage genome architecture, gene function, capsid structure, gene mobility, intron splicing, and evolution.
PMCID: PMC3706429  PMID: 23874930
25.  Keto-Mycolic Acid-Dependent Pellicle Formation Confers Tolerance to Drug-Sensitive Mycobacterium tuberculosis 
mBio  2013;4(3):e00222-13.
The chronic nature of tuberculosis (TB), its requirement of long duration of treatment, its ability to evade immune intervention, and its propensity to relapse after drug treatment is discontinued are reminiscent of other chronic, biofilm-associated bacterial diseases. Historically, Mycobacterium tuberculosis was grown as a pellicle, a biofilm-like structure, at the liquid-air interface in a variety of synthetic media. Notably, the most widely administered human vaccine, BCG, is grown as a pellicle for vaccine production. However, the molecular requirements for this growth remain ill defined. Here, we demonstrate that keto-mycolic acids (keto-MA) are essential for pellicle growth, and mutants lacking in or depleted of this MA species are unable to form a pellicle. We investigated the role of the pellicle biofilm in the reduction of antibiotic sensitivity known as drug tolerance using the pellicle-defective ΔmmaA4 mutant strain. We discovered that the ΔmmaA4 mutant, which is both pellicle defective and highly sensitive to rifampicin (RIF) under planktonic growth, when incorporated within the wild-type pellicle biofilm, was protected from the bactericidal activity of RIF. The observation that growth within the M. tuberculosis pellicle biofilm can confer drug tolerance to a drug-hypersensitive strain suggests that identifying molecular requirements for pellicle growth could lead to development of novel interventions against mycobacterial infections. Our findings also suggest that a class of drugs that can disrupt M. tuberculosis biofilm formation, when used in conjunction with conventional antibiotics, has the potential to overcome drug tolerance.
Two of the most important questions in tuberculosis (TB) research are (i) how does Mycobacterium tuberculosis persist in the human host for decades in the face of an active immune response and (ii) why does it take six months and four drugs to treat uncomplicated TB. Both these aspects of M. tuberculosis biology are reminiscent of infections caused by organisms capable of forming biofilms. M. tuberculosis is capable of growing as a biofilm-like structure called the pellicle. In this study, we demonstrate that a specific cell wall component, keto-mycolic acid, is essential for pellicle growth. We also demonstrate that a strain of M. tuberculosis that is both drug sensitive and pellicle defective exhibits commensal behavior and becomes drug tolerant by becoming part of a heterogeneous pellicle, a characteristic of multispecies biofilms. These observations could have important implications for identifying novel pathways for M. tuberculosis drug tolerance and the design of new modalities to rapidly treat TB.
PMCID: PMC3663190  PMID: 23653446

Results 1-25 (63)