Bactericidal Activity of Multilayered Hybrid Structures Comprising Titania Nanoparticles and CdSe Quantum Dots under Visible Light

Titania nanoparticle/CdSe quantum dot hybrid structures are a promising bactericidal coating that exhibits a pronounced effect against light-sensitive bacteria. Here, we report the results of a comprehensive study of the photophysical properties and bactericidal functionality of these hybrid structures on various bacterial strains. We found that our structures provide the efficient generation of superoxide anions under the action of visible light due to electron transfer from QDs to titania nanoparticles with ~60% efficiency. We also tested the antibacterial activity of hybrid structures on five strains of bacteria. The formed structures combined with visible light irradiation effectively inhibit the growth of Escherichia coli, Bacillus subtilis, and Mycobacterium smegmatis bacteria, the last of which is a photosensitive causative agent model of tuberculosis.

Lag Phase Is a Dynamic, Organized, Adaptive, and Evolvable Period That Prepares Bacteria for Cell Division

Lag is a temporary period of nonreplication seen in bacteria that are introduced to new media. Despite latency being described by Müller in 1895, only recently have we gained insights into the cellular processes characterizing lag phase. This review covers literature to date on the transcriptomic, proteomic, metabolomic, physiological, biochemical, and evolutionary features of prokaryotic lag. Though lag is commonly described as a preparative phase that allows bacteria to harvest nutrients and adapt to new environments, the implications of recent studies indicate that a refinement of this view is well deserved. As shown, lag is a dynamic, organized, adaptive, and evolvable process that protects bacteria from threats, promotes reproductive fitness, and is broadly relevant to the study of bacterial evolution, host-pathogen interactions, antibiotic tolerance, environmental biology, molecular microbiology, and food safety.

Lag phase-associated iron accumulation is likely a microbial counter-strategy to host iron sequestration: role of the ferric uptake regulator (fur)

Iron is an essential metal for almost all forms of life, but potentiates oxidative stress via Fenton catalysis. During microbial lag phase there is a rapid influx of iron with concomitant oxidative hypersensitivity. How and why iron accumulation occurs remains to be elucidated. Iron homeostasis in prokaryotes is mediated by the ferric uptake regulator (Fur), an iron-activated global regulator that controls intracellular iron levels by feedback inhibition with the metal. Herein it is postulated, based on the expression profiles of antioxidant enzymes within the Fur regulon as observed in wild type and Δfur mutants, that iron accumulation is mediated by a transitively low concentration of the Fur protein during lag phase. Vertebrate hosts sequester iron upon 'sensing' an infection in order to retard microbial proliferation through a process known as 'nutritional immunity'. It is herein argued that the purpose of iron accumulation is not principally a preparative step for the replicative phase, as suggested elsewhere, but an evolved behavior that counteracts host iron sequestration. This interpretation is supported by multiple clinical and animal studies that demonstrate that iron surplus in hosts advances progression and susceptibility to infection, and vice versa. Contextualizing iron accumulation as a counter-immune behavior adds impetus to the development of antibiotics targeting pathogenic modes of iron acquisition.