Browsing by Author "Wang, Xifan"

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    Bacterial Endospores as Phage Genome Carriers and Protective Shells
    (American Society for Microbiology, 2018) Gabiatti, Naiana; Yu, Pingfeng; Mathieu, Jacques; Lu, Grant W.; Wang, Xifan; Zhang, Hangjun; Soares, Hugo M.; Alvarez, Pedro J.J.
    Bacterial endospores can serve as phage genome protection shells against various environmental stresses to enhance microbial control applications. The genomes of polyvalent lytic Bacillus phages PBSC1 and PBSC2, which infect both B. subtilis subsp. subtilis and B. cereusNRS 248, were incorporated into B. subtilis endospores (without integration into the host chromosome). When PBSC1 and PBSC2 were released from germinating endospores, they significantly inhibited the growth of the targeted opportunistic pathogen B. cereus Optimal endospore entrapment was achieved when phages were introduced to the fast-sporulating prespores at a multiplicity of infection of 1. Longer endospore maturation (48 h versus 24 h) increased both spore yield and efficiency of entrapment. Compared with free phages, spore-protected phage genomes showed significantly higher resistance toward high temperatures (60 to 80°C), extreme pH (pH 2 or pH 12), and copper ions (0.1 to 10 mg/liter). Endospore germination is inducible by low concentrations of l-alanine or by a germinant mixture (l-asparagine, d-glucose, d-fructose, and K+) to trigger the expression, assembly, and consequent release of phage particles within 60 to 90 min. Overall, the superior resiliency of polyvalent phages protected by endospores might enable nonrefrigerated phage storage and enhance phage applications after exposure to adverse environmental conditions.IMPORTANCE: Bacteriophages are being considered for the control of multidrug-resistant and other problematic bacteria in environmental systems. However, the efficacy of phage-based microbial control is limited by infectivity loss during phage delivery and/or storage. Here, we exploit the pseudolysogenic state of phages, which involves incorporation of their genome into bacterial endospores (without integration into the host chromosome), to enhance survival in unfavorable environments. We isolated polyvalent (broad-host-range) phages that efficiently infect both benign and opportunistically pathogenic Bacillusstrains and encapsulated the phage genomes in B. subtilis endospores to significantly improve resistance to various environmental stressors. Encapsulation by spores also significantly enhanced phage genome viability during storage. We also show that endospore germination can be induced on demand with nutrient germinants that trigger the release of active phages. Overall, we demonstrate that encapsulation of polyvalent phage genomes into benign endospores holds great promise for broadening the scope and efficacy of phage biocontrol.
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    Photothermoelectric Effects in Gold Nanostructures
    (2020-10-15) Wang, Xifan; Natelson, Douglas
    Nanostructures in noble metals(e.g Au,Ag) provide unique properties for emergingapplications. One of the most important and interesting properties is the plasmonicresponse, where the electron gas in the metal can couple with electromagnetic radia-tion of wavelengths that are far larger than the nanostructure size. As a result, thelocal electric field can be significantly enhanced. Due to this property, the nanostruc-tured metal device can be locally heated by an incident light, and cause electrons totravel through the device. By measuring the electronic transport and open circuitvoltage, the characteristics of this photothermoelectric effects can be well studied. Ifone can raster-scan the laser and probe the response of the device as a function ofthe laser position, the variation of photothermoelectric response along the nanostruc-tured device can be collected. In this dissertation, I mainly focused on the study ofphotothermoelectric effects in the gold nanowire. We observed that the photother-moelectric response varies when scanning across the gold nanowire with a focusedlaser beam. Such a phenomena can be possible caused by local Seebeck coefficientvariation. After annealing the device with relatively low temperature (200◦C), theoverall intensity of PTE response is significantly reduced. This result indicates that a major contribution to the local Seebeck coefficient is residual strain along the device.Moreover, we modified the surface of the gold nanowire with different methods and successfully ruled out some other factors, which can potentially cause this phenomena.