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Bifidobacteria represent a dominant constituent of human gut microbiomes during infancy, influencing nutrition, immune development, and resistance to infection. Despite interest in bifidobacteria as a live biotic therapy, our understanding of colonization, host-microbe interactions, and the health-promoting effects of bifidobacteria is limited. To address these major knowledge gaps, we used a large-scale genetic approach to create a mutant fitness compendium in Bifidobacterium breve. First, we generated a high-density randomly barcoded transposon insertion pool and used it to determine fitness requirements during colonization of germ-free mice and chickens with multiple diets and in response to hundreds of in vitro perturbations. Second, to enable mechanistic investigation, we constructed an ordered collection of insertion strains covering 1,462 genes. We leveraged these tools to reveal community- and diet-specific requirements for colonization and to connect the production of immunomodulatory molecules to growth benefits. These resources will catalyze future investigations of this important beneficial microbe. 

Transient heat fluxes in cutting-edge computing systems, electromagnetic switches, and diode-pumped lasers can exceed 50 MW/m2, which is nearly the heat flux radiated by the Sun. To manage extreme thermal loads, the State-of-the-Art is to boil and evaporate liquid coolants on micro- and nano-structured heat sinks. This work demonstrates the application of laser-scanning fluorescence thermography to identify the spatiotemporal limits of local, transient hot-spot cooling with impinging pulsed micro-jets and sprays. The laser-scanning fluorescence thermography measurements are based on the fluorescence of PS microspheres and quantum-dot thin-films deposited on FTO-glass heater substrates. The fluorescence-based thermometers are subsequently coated with either Hafnium (Hf) or Titanium (Ti) metal thin-films, serving as both protective coatings and the heater surfaces at near critical heat flux conditions. This work also discusses the fabrication procedure of the fluorescence heater/thermometers with micro-mesh heater surfaces and the corresponding pulsed-jet-boiling data via IR thermography. 

ABSTRACT Here, we investigate an unusual antiviral mechanism developed in the bacterium Streptomyces griseus . SgrAI is a type II restriction endonuclease that forms run-on oligomer filaments when activated and possesses both accelerated DNA cleavage activity and expanded DNA sequence specificity. Mutations disrupting the run-on oligomer filament eliminate the robust antiphage activity of wild-type SgrAI, and the observation that even relatively modest disruptions completely abolish this anti-viral activity shows that the greater speed imparted by the run-on oligomer filament mechanism is critical to its biological function. Simulations of DNA cleavage by SgrAI uncover the origins of the kinetic advantage of this newly described mechanism of enzyme regulation over more conventional mechanisms, as well as the origin of the sequestering effect responsible for the protection of the host genome against damaging DNA cleavage activity of activated SgrAI. IMPORTANCE This work is motivated by an interest in understanding the characteristics and advantages of a relatively newly discovered enzyme mechanism involving filament formation. SgrAI is an enzyme responsible for protecting against viral infections in its host bacterium and was one of the first such enzymes shown to utilize such a mechanism. In this work, filament formation by SgrAI is disrupted, and the effects on the speed of the purified enzyme as well as its function in cells are measured. It was found that even small disruptions, which weaken but do not destroy filament formation, eliminate the ability of SgrAI to protect cells from viral infection, its normal biological function. Simulations of enzyme activity were also performed and show how filament formation can greatly speed up an enzyme’s activation compared to that of other known mechanisms, as well as to better localize its action to molecules of interest, such as invading phage DNA.