Bacteriophage最新文献

Coliphage HK022 excludes phage λ by subverting the λ antitermination system and arresting transcription on the λ chromosome. The 12 kDa HK022 Nun protein binds to λ nascent transcript through its N-terminal Arginine Rich Motif (ARM), blocking access by λ N and arresting transcription via a C-terminal interaction with RNA polymerase. In a purified in vitro system, we recently demonstrated that Nun arrests transcription by restricting lateral movement of transcription elongation complex (TEC) along the DNA register, thereby freezing the translocation state. We will discuss some of the key experiments that led to this conclusion, as well as present additional results that further support it.

Exposure to narrowband violet-blue light around 405 nm wavelength can induce lethal oxidative damage to bacteria and fungi, however effects on viruses are unknown. As photosensitive porphyrin molecules are involved in the microbicidal inactivation mechanism, and since porphyrins are absent in viruses, then any damaging effects of 405 nm light on viruses might appear unlikely. This study used the bacteriophage ɸC31, as a surrogate for non-enveloped double-stranded DNA viruses, to establish whether 405 nm light can induce virucidal effects. Exposure of ɸC31 suspended in minimal media, nutrient-rich media, and porphyrin solution, demonstrated differing sensitivity of the phage. Significant reductions in phage titer occurred when exposed in nutrient-rich media, with ~3-, 5- and 7-log₁₀ reductions achieved after exposure to doses of 0.3, 0.5 and 1.4 kJ/cm², respectively. When suspended in minimal media a 0.3-log₁₀ reduction (P = 0.012) occurred after exposure to 306 J/cm²: much lower than the 2.7- and > 2.5-log₁₀ reductions achieved with the same dose in nutrient-rich, and porphyrin-supplemented media, suggesting inactivation is accelerated by the photo-activation of light-sensitive components in the media. This study provides the first evidence of the interaction of narrowband 405 nm light with viruses, and demonstrates that viral susceptibility to 405 nm light can be significantly enhanced by involvement of exogenous photosensitive components. The reduced susceptibility of viruses in minimal media, compared with that of other microorganisms, provides further evidence that the antimicrobial action of 405 nm light is predominantly due to the photo-excitation of endogenous photosensitive molecules such as porphyrins within susceptible microorganisms.

Bacteriophages have an essential gene kit that enables their invasion, replication, and production. In addition to this "core" genome, they can carry "accessory" genes that dramatically impact bacterial biology, and presumably boost their own success. The content of phage genomes continue to surprise us by revealing new ways that viruses impact bacterial biology. The genome of a Clostridium difficile myovirus, phiCDHM1, contains homologs of three bacterial accessory gene regulator (agr) genes. The agr system is a type of quorum sensing (QS), via which the phage may modify C. difficile interactions with its environment. Although their mechanism of action is unknown, mutants in bacterial versions of these genes impact sporulation and virulence. To explore how phage QS genes may influence C. difficile biology, we examine the main categories of bacterial behavior that phages have been shown to influence and discuss how interactions via QS could influence behavior at a wider level.

Transcription initiation is the central point of gene expression regulation. Understanding of molecular mechanism of transcription regulation requires, ultimately, the structural understanding of consequences of transcription factors binding to DNA-dependent RNA polymerase (RNAP), the enzyme of transcription. We recently determined a structure of a complex between transcription factor gp39 encoded by a Thermus bacteriophage and Thermus RNAP holoenzyme. In this addendum to the original publication, we highlight structural insights that explain the ability of gp39 to act as an RNAP specificity switch which inhibits transcription initiation from a major class of bacterial promoters, while allowing transcription from a minor promoter class to continue.

Phage amplification detected by MALDI-TOF MS was investigated for rapid and simultaneous Burkholderia pseudomallei identification and ceftazidime resistance determination. B. pseudomallei ceftazidime susceptible and resistant ΔpurM mutant strains Bp82 and Bp82.3 were infected with broadly targeting B. pseudomallei phage ϕX216 and production of the m/z 37.6 kDa phage capsid protein observed by MALDI-TOF MS over the course of 3 h infections. This allowed for repoducible phage-based bacterial ID within 2 h of the onset of infection. MALDI-TOF MS-measured time to detection correlated with in silico modeling, which predicted an approximate 2 h detection time. Ceftazidime susceptible strain Bp82, while detectable in the absence of the drug, owing to the reliance of phage amplification on a viable host, was not detectable when 10 μg/mL ceftazidime was added at the onset of infection. In contrast, resistant strain Bp82.3 was detected in the same 2 h timeframe both with and without the addition of ceftazidime.

Viruses from extreme environments are still largely unexplored and may harbor unseen genetic potential. Here, we present a first glance at the morphological diversity of virus like particles (VLPs) from an environment that is extreme in more than one respect: two recently discovered hydrothermal vent fields on the East Scotia Ridge in the Southern Ocean near Antarctica. They are the southernmost hydrothermal sites found to date and have been shown to present a new biogeographic province, containing several new macrofaunal species and associated microbial organisms. Transmission electron microscopy revealed a range of tailed and untailed VLPs of various morphologies as well as an unusual long rod-shaped VLP with three long filaments. Based on its distant similarity with several known archaeal viruses, we hypothesize that this presents a new viral morphology that most likely infects an archaeon. Notably absent in the samples we analyzed were lemon- or spindle-shaped VLPs that have previously been described in other hydrothermal vent settings.

Gene 6 protein of bacteriophage T7 has 5'-3'-exonuclease activity specific for duplex DNA. We have found that gene 6 protein also has flap endonuclease activity. The flap endonuclease activity is considerably weaker than the exonuclease activity. Unlike the human homolog of gene 6 protein, the flap endonuclease activity of gene 6 protein is dependent on the length of the 5'-flap. This dependency of activity on the length of the 5'-flap may result from the structured helical gateway region of gene 6 protein which differs from that of human flap endonuclease 1. The flap endonuclease activity provides a mechanism by which RNA-terminated Okazaki fragments, displaced by the lagging strand DNA polymerase, are processed. 3'-extensions generated during degradation of duplex DNA by the exonuclease activity of gene 6 protein are inhibitory to further degradation of the 5'-terminus by the exonuclease activity of gene 6 protein. The single-stranded DNA binding protein of T7 overcomes this inhibition.