Structural basis of Qng1-mediated salvage of the micronutrient queuine from queuosine-5'-monophosphate as the biological substrate.

Eukaryotic life benefits from-and ofttimes critically relies upon-the de novo biosynthesis and supply of vitamins and micronutrients from bacteria. The micronutrient queuosine (Q), derived from diet and/or the gut microbiome, is used as a source of the nucleobase queuine, which once incorporated into the anticodon of tRNA contributes to translational efficiency and accuracy. Here, we report high-resolution, substrate-bound crystal structures of the Sphaerobacter thermophilus queuine salvage protein Qng1 (formerly DUF2419) and of its human ortholog QNG1 (C9orf64), which together with biochemical and genetic evidence demonstrate its function as the hydrolase releasing queuine from queuosine-5'-monophosphate as the biological substrate. We also show that QNG1 is highly expressed in the liver, with implications for Q salvage and recycling. The essential role of this family of hydrolases in supplying queuine in eukaryotes places it at the nexus of numerous (patho)physiological processes associated with queuine deficiency, including altered metabolism, proliferation, differentiation and cancer progression.

7-Deazaguanines in DNA: functional and structural elucidation of a DNA modification system.

The modified nucleosides 2'-deoxy-7-cyano- and 2'-deoxy-7-amido-7-deazaguanosine (dPreQ0 and dADG, respectively) recently discovered in DNA are the products of the bacterial queuosine tRNA modification pathway and the dpd gene cluster, the latter of which encodes proteins that comprise the elaborate Dpd restriction-modification system present in diverse bacteria. Recent genetic studies implicated the dpdA, dpdB and dpdC genes as encoding proteins necessary for DNA modification, with dpdD-dpdK contributing to the restriction phenotype. Here we report the in vitro reconstitution of the Dpd modification machinery from Salmonella enterica serovar Montevideo, the elucidation of the roles of each protein and the X-ray crystal structure of DpdA supported by small-angle X-ray scattering analysis of DpdA and DpdB, the former bound to DNA. While the homology of DpdA with the tRNA-dependent tRNA-guanine transglycosylase enzymes (TGT) in the queuosine pathway suggested a similar transglycosylase activity responsible for the exchange of a guanine base in the DNA for 7-cyano-7-deazaguanine (preQ0), we demonstrate an unexpected ATPase activity in DpdB necessary for insertion of preQ0 into DNA, and identify several catalytically essential active site residues in DpdA involved in the transglycosylation reaction. Further, we identify a modification site for DpdA activity and demonstrate that DpdC functions independently of DpdA/B in converting preQ0-modified DNA to ADG-modified DNA.

Compounding Achromobacter Phages for Therapeutic Applications.

Achromobacter species colonization of Cystic Fibrosis respiratory airways is an increasing concern. Two adult patients with Cystic Fibrosis colonized by Achromobacter xylosoxidans CF418 or Achromobacter ruhlandii CF116 experienced fatal exacerbations. Achromobacter spp. are naturally resistant to several antibiotics. Therefore, phages could be valuable as therapeutics for the control of Achromobacter. In this study, thirteen lytic phages were isolated and characterized at the morphological and genomic levels for potential future use in phage therapy. They are presented here as the Achromobacter Kumeyaay phage collection. Six distinct Achromobacter phage genome clusters were identified based on a comprehensive phylogenetic analysis of the Kumeyaay collection as well as the publicly available Achromobacter phages. The infectivity of all phages in the Kumeyaay collection was tested in 23 Achromobacter clinical isolates; 78% of these isolates were lysed by at least one phage. A cryptic prophage was induced in Achromobacter xylosoxidans CF418 when infected with some of the lytic phages. This prophage genome was characterized and is presented as Achromobacter phage CF418-P1. Prophage induction during lytic phage preparation for therapy interventions require further exploration. Large-scale production of phages and removal of endotoxins using an octanol-based procedure resulted in a phage concentrate of 1 × 109 plaque-forming units per milliliter with an endotoxin concentration of 65 endotoxin units per milliliter, which is below the Food and Drugs Administration recommended maximum threshold for human administration. This study provides a comprehensive framework for the isolation, bioinformatic characterization, and safe production of phages to kill Achromobacter spp. in order to potentially manage Cystic Fibrosis (CF) pulmonary infections.

Gp4 is a nuclease required for morphogenesis of T4-like bacteriophages.

An essential step in the morphogenesis of tailed bacteriophages is the joining of heads and tails to form infectious virions. Our understanding of the maturation of complete virus particles remains incomplete. Through an unknown mechanism, phage T4 gene product 4 (gp4) plays an essential role in the head-tail joining step of T4-like phages. Alignment of T4 gp4 homologs identified a type II restriction endonuclease motif. Purified gp4 from both T4 and a marine T4-like bacteriophage, YC, have non-specific nuclease activity in vitro. Mutation of a single conserved amino acid residue in the endonuclease fold of T4 and YC gp4 abrogates nuclease activity. When expressed in trans, the wild type T4 gp4, but neither the mutated T4 protein nor the YC homolog, rescues a T4 gene 4 amber mutant phage. Thus the nuclease activity appears essential for morphogenesis, potentially by cleaving packaged DNA to enable the joining of heads to tails.

A diversity-generating retroelement encoded by a globally ubiquitous Bacteroides phage.

BACKGROUND: Diversity-generating retroelements (DGRs) are genetic cassettes that selectively mutate target genes to produce hypervariable proteins. First characterized in Bordetella bacteriophage BPP-1, the DGR creates a hypervariable phage tail fiber that enables host tropism switching. Subsequent surveys for DGRs conclude that the majority identified to date are bacterial or archaeal in origin. This work examines bacteriophage and bacterial genomes for novel phage-encoded DGRs. RESULTS: This survey discovered 92 DGRs that were only found in phages exhibiting a temperate lifestyle. The majority of phage-encoded DGRs were identified as prophages in bacterial hosts from the phyla Bacteroidetes, Proteobacteria, and Firmicutes. Sequence reads from these previously unidentified prophages were present in viral metagenomes (viromes), indicating these prophages can produce functional viruses. Five phages possessed hypervariable proteins with structural similarity to the tail fiber of BPP-1, whereas the functions of the remaining DGR target proteins were unknown. A novel temperate phage that harbors a DGR cassette targeting a protein of unknown function was induced from Bacteroides dorei. This phage, here named Bacteroides dorei Hankyphage, lysogenizes 13 different Bacteroides species and was present in 34% and 21% of whole-community metagenomes and human-associated viromes, respectively. CONCLUSIONS: Here, the number of known DGR-containing phages is increased from four to 92. All of these phages exhibit a temperate lifestyle, including a cosmopolitan human-associated phage. Targeted hypervariation by temperate phages may be a ubiquitous mechanism underlying phage-bacteria interaction in the human microbiome.

Phage on tap-a quick and efficient protocol for the preparation of bacteriophage laboratory stocks.

A major limitation with traditional phage preparations is the variability in titer, salts, and bacterial contaminants between successive propagations. Here we introduce the Phage On Tap (PoT) protocol for the quick and efficient preparation of homogenous bacteriophage (phage) stocks. This method produces homogenous, laboratory-scale, high titer (up to 10(10-11) PFU·ml(-1)), endotoxin reduced phage banks that can be used to eliminate the variability between phage propagations and improve the molecular characterizations of phage. The method consists of five major parts, including phage propagation, phage clean up by 0.22 µm filtering and chloroform treatment, phage concentration by ultrafiltration, endotoxin removal, and the preparation and storage of phage banks for continuous laboratory use. From a starting liquid lysate of > 100 mL, the PoT protocol generated a clean, homogenous, laboratory phage bank with a phage recovery efficiency of 85% within just two days. In contrast, the traditional method took upwards of five days to produce a high titer, but lower volume phage stock with a recovery efficiency of only 4%. Phage banks can be further purified for the removal of bacterial endotoxins, reducing endotoxin concentrations by over 3,000-fold while maintaining phage titer. The PoT protocol focused on T-like phages, but is broadly applicable to a variety of phages that can be propagated to sufficient titer, producing homogenous, high titer phage banks that are applicable for molecular and cellular assays.