Characterization of a nucleotide kinase encoded by bacteriophage T7

Molecular characterization of Drosophila melanogaster thymidylate kinase

Drosophila has been used as an animal model to study pathogenic mechanism of neurological disorders. Thymidylate kinase (TMPK) is an essential enzyme in dTTP synthesis catalyzing the phosphorylation of dTMP to dTDP. Loss of function mutations in the DTYMK gene, coding for TMPK, cause severe microcephaly in human patients. In this study, Drosophila melanogaster TMPK (DmTMPK) was cloned, expressed, purified and characterized. Unlike human TMPK, DmTMPK phosphorylated not only dTMP and dUMP but also dGMP and dIMP although with low efficiency. ATP and dATP are the most efficient phosphate donor but at higher concentration (>1 mM) ATP inhibited DmTMPK activity. Sequence and structural model analysis explain why DmTMPK could phosphorylate purine nucleoside monophosphates. This study has laid a solid foundation for future study of TMPK function in Drosophila.

A genome-wide overexpression screen reveals Mycobacterium smegmatis growth inhibitors encoded by mycobacteriophage Hammy

During infection, bacteriophages produce diverse gene products to overcome bacterial antiphage defenses, to outcompete other phages, and to take over cellular processes. Even in the best-studied model phages, the roles of most phage-encoded gene products are unknown, and the phage population represents a largely untapped reservoir of novel gene functions. Considering the sheer size of this population, experimental screening methods are needed to sort through the enormous collection of available sequences and identify gene products that can modulate bacterial behavior for downstream functional characterization. Here, we describe the construction of a plasmid-based overexpression library of 94 genes encoded by Hammy, a Cluster K mycobacteriophage closely related to those infecting clinically important mycobacteria. The arrayed library was systematically screened in a plate-based cytotoxicity assay, identifying a diverse set of 24 gene products (representing ∼25% of the Hammy genome) capable of inhibiting growth of the host bacterium Mycobacterium smegmatis. Half of these are related to growth inhibitors previously identified in related phage Waterfoul, supporting their functional conservation; the other genes represent novel additions to the list of known antimycobacterial growth inhibitors. This work, conducted as part of the HHMI-supported Science Education Alliance Gene-function Exploration by a Network of Emerging Scientists (SEA-GENES) project, highlights the value of parallel, comprehensive overexpression screens in exploring genome-wide patterns of phage gene function and novel interactions between phages and their hosts.

Systematic overexpression of genes encoded by mycobacteriophage Waterfoul reveals novel inhibitors of mycobacterial growth

Bacteriophages represent an enormous reservoir of novel genes, many of which are unrelated to existing entries in public databases and cannot be assigned a predicted function. Characterization of these genes can provide important insights into the intricacies of phage-host interactions and may offer new strategies to manipulate bacterial growth and behavior. Overexpression is a useful tool in the study of gene-mediated effects, and we describe here the construction of a plasmid-based overexpression library of a complete set of genes for Waterfoul, a mycobacteriophage closely related to those infecting clinically important strains of Mycobacterium tuberculosis and/or Mycobacterium abscessus. The arrayed Waterfoul gene library was systematically screened in a plate-based cytotoxicity assay, identifying a diverse set of 32 Waterfoul gene products capable of inhibiting the growth of the host Mycobacterium smegmatis and providing a first look at the frequency and distribution of cytotoxic products encoded within a single mycobacteriophage genome. Several of these Waterfoul gene products were observed to confer potent anti-mycobacterial effects, making them interesting candidates for follow-up mechanistic studies.

Characterization, genome analysis and in vitro activity of a novel phage vB_EcoA_RDN8.1 active against multi-drug resistant and extensively drug-resistant biofilm-forming uropathogenic Escherichia coli isolates, India

AIM

We aimed to study host range, stability, genome and antibiofilm activity of a novel phage vB_EcoA_RDN8.1 active against multi-drug resistant (MDR) and extensively drug-resistant (XDR) biofilm-forming uropathogenic Escherichia coli isolates.

METHODS AND RESULTS

A novel lytic phage vB_EcoA_RDN8.1 active against UPEC strains resistant to third-generation cephalosporins, fluoroquinolones, aminoglycosides, imipenem, beta-lactamase inhibitor combination and polymyxins was isolated from community raw sewage water of Chandigarh. It exhibited a clear plaque morphology and a burst size of 250. In the time-kill assay, the maximum amount of killing was achieved at MOI 1.0. vB_EcoA_RDN8.1 belongs to the family Autographiviridae, has a genome size of 39.5 kb with a GC content of 51.6%. It was stable over a wide range of temperatures and pH. It was able to inhibit biofilm formation which may be related to an endolysin encoded by ORF 19.

CONCLUSIONS

The vB_EcoA_RDN8.1 is a novel lytic phage that has the potential for inclusion into phage cocktails being developed for the treatment of urinary tract infections (UTIs) caused by highly drug-resistant UPEC.

SIGNIFICANCE AND IMPACT OF THE STUDY

We provide a detailed characterization of a novel lytic Escherichia phage with antibiofilm activity having a potential application against MDR and XDR UPEC causing UTIs.

Origin and Evolution of Studiervirinae Bacteriophages Infecting Pectobacterium: Horizontal Transfer Assists Adaptation to New Niches

Black leg and soft rot are devastating diseases causing up to 50% loss of potential potato yield. The search for, and characterization of, bacterial viruses (bacteriophages) suitable for the control of these diseases is currently a sought-after task for agricultural microbiology. Isolated lytic Pectobacterium bacteriophages Q19, PP47 and PP81 possess a similar broad host range but differ in their genomic properties. The genomic features of characterized phages have been described and compared to other Studiervirinae bacteriophages. Thorough phylogenetic analysis has clarified the taxonomy of the phages and their positioning relative to other genera of the Autographiviridae family. Pectobacterium phage Q19 seems to represent a new genus not described previously. The genomes of the phages are generally similar to the genome of phage T7 of the Teseptimavirus genus but possess a number of specific features. Examination of the structure of the genes and proteins of the phages, including the tail spike protein, underlines the important role of horizontal gene exchange in the evolution of these phages, assisting their adaptation to Pectobacterium hosts. The results provide the basis for the development of bacteriophage-based biocontrol of potato soft rot as an alternative to the use of antibiotics.

It seems like only yesterday

I spent my childhood and adolescence in North and South Carolina, attended Duke University, and then entered Duke Medical School. One year in the laboratory of George Schwert in the biochemistry department kindled my interest in biochemistry. After one year of residency on the medical service of Duke Hospital, chaired by Eugene Stead, I joined the group of Arthur Kornberg at Stanford Medical School as a postdoctoral fellow. Two years later I accepted a faculty position at Harvard Medical School, where I remain today. During these 50 years, together with an outstanding group of students, postdoctoral fellows, and collaborators, I have pursued studies on DNA replication. I have experienced the excitement of discovering a number of important enzymes in DNA replication that, in turn, triggered an interest in the dynamics of a replisome. My associations with industry have been stimulating and fostered new friendships. I could not have chosen a better career.

Genetic requirements for sensitivity of bacteriophage t7 to dideoxythymidine

We previously reported that the presence of dideoxythymidine (ddT) in the growth medium selectively inhibits the ability of bacteriophage T7 to infect Escherichia coli by inhibiting phage DNA synthese (N. Q. Tran, L. F. Rezende, U. Qimron, C. C. Richardson, and S. Tabor, Proc. Natl. Acad. Sci. U. S. A. 105:9373-9378, 2008, doi:10.1073/pnas.0804164105). In the presence of T7 gene 1.7 protein, ddT is taken up into the E. coli cell and converted to ddTTP. ddTTP is incorporated into DNA as ddTMP by the T7 DNA polymerase, resulting in chain termination. We have identified the pathway by which exogenous ddT is converted to ddTTP. The pathway consists of ddT transport by host nucleoside permeases and phosphorylation to ddTMP by the host thymidine kinase. T7 gene 1.7 protein phosphorylates ddTMP and ddTDP, resulting in ddTTP. A 74-residue peptide of the gene 1.7 protein confers ddT sensitivity to the same extent as the 196-residue wild-type gene 1.7 protein. We also show that cleavage of thymidine to thymine and deoxyribose-1-phosphate by the host thymidine phosphorylase greatly increases the sensitivity of phage T7 to ddT. Finally, a mutation in T7 DNA polymerase that leads to discrimination against the incorporation of ddTMP eliminates ddT sensitivity.