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Although the transport and mixing of proteins and other molecules inside bacteria rely on the diffusion of molecules, many aspects of the molecular diffusion in bacterial cytoplasm remain unclear or controversial, including how the diffusion-temperature relation follows the Stokes-Einstein equation. In this study, we applied single-particle tracking photoactivated localization microscopy to investigate the diffusion of histonelike nucleoid structuring (HNS) proteins and free dyes in bacterial cytoplasm at different temperatures. Although the diffusion of HNS proteins in both live and dead bacteria increased at higher temperatures and appeared to follow the Arrhenius equation, the diffusion of free dyes decreased at higher temperatures, questioning the previously proposed theories based on superthermal fluctuations. To understand the measured diffusion-temperature relations, we developed an alternative model, in which the bacterial cytoplasm is considered as a polymeric network or mesh. In our model, the Stokes-Einstein equation remains valid, while the polymeric network contributes a significant term to the viscosity experienced by the molecules diffusing in bacterial cytoplasm. Our model was successful in predicting the diffusion-temperature relations for both HNS proteins and free dyes in bacteria. In addition, we systematically examined the predicted diffusion-temperature relations with different parameters in the model, and predicted the possible existence of phase transitions.

The antimicrobial activity and mechanism of silver ions (Ag + ) have gained broad attention in recent years. However, dynamic studies are rare in this field. Here, we report our measurement of the effects of Ag + ions on the dynamics of histone-like nucleoid-structuring (H-NS) proteins in live bacteria using single-particle-tracking photoactivated localization microscopy (sptPALM). It was found that treating the bacteria with Ag + ions led to faster diffusive dynamics of H-NS proteins. Several techniques were used to understand the mechanism of the observed faster dynamics. Electrophoretic mobility shift assay on purified H-NS proteins indicated that Ag + ions weaken the binding between H-NS proteins and DNA. Isothermal titration calorimetry confirmed that DNA and Ag + ions interact directly. Our recently developed sensing method based on bent DNA suggested that Ag + ions caused dehybridization of double-stranded DNA (i.e., dissociation into single strands). These evidences led us to a plausible mechanism for the observed faster dynamics of H-NS proteins in live bacteria when subjected to Ag + ions: Ag + -induced DNA dehybridization weakens the binding between H-NS proteins and DNA. This work highlighted the importance of dynamic study of single proteins in live cells for understanding the functions of antimicrobial agents in bacteria. IMPORTANCE As so-called "superbug" bacteria resistant to commonly prescribed antibiotics have become a global threat to public health in recent years, noble metals, such as silver, in various forms have been attracting broad attention due to their antimicrobial activities. However, most of the studies in the existing literature have relied on the traditional bioassays for studying the antimicrobial mechanism of silver; in addition, temporal resolution is largely missing for understanding the effects of silver on the molecular dynamics inside bacteria. Here, we report our study of the antimicrobial effect of silver ions at the nanoscale on the diffusive dynamics of histone-like nucleoid-structuring (H-NS) proteins in live bacteria using single-particle-tracking photoactivated localization microscopy. This work highlights the importance of dynamic study of single proteins in live cells for understanding the functions of antimicrobial agents in bacteria., (Copyright © 2020 American Society for Microbiology.)

Silver nanoparticles (AgNPs) and ions (Ag + ) have recently gained broad attention due to their antimicrobial effects against bacteria and other microbes. In this work, we demonstrate the use of super-resolution fluorescence microscopy for investigating and quantifying the antimicrobial effect of AgNPs at the molecular level. We found that subjecting Escherichia coli (E. coli) bacteria to AgNPs led to nanoscale reorganization of histone-like nucleoid structuring (H-NS) proteins, an essential nucleoid associated protein in bacteria. We observed that H-NS proteins formed denser and larger clusters at the center of the bacteria after exposure to AgNPs. We quantified the spatial reorganizations of H-NS proteins by examining the changes of various spatial parameters, including the inter-molecular distances and molecular densities. Clustering analysis based on Voronoi-tessellation were also performed to characterize the change of H-NS proteins' clustering behavior. We found that AgNP-treatment led to an increase in the fraction of H-NS proteins forming clusters. Similar effects were observed for bacteria exposed to Ag + ions, suggesting that the release of Ag + ions plays an important role in the toxicity of AgNPs. On the other hand, we observed that AgNPs with two surface coatings showed difference in the nanoscale reorganization of H-NS proteins, indicating that particle-specific effects also contribute to the antimicrobial activities of AgNPs. Our results suggested that H-NS proteins were significantly affected by AgNPs and Ag + ions, which has been overlooked previously. In addition, we examined the dynamic motion of AgNPs that were attached to the surface of bacteria. We expect that the current methodology can be readily applied to broadly and quantitatively study the spatial reorganization of biological macromolecules at the scale of nanometers caused by metal nanoparticles, which are expected to shed new light on the antimicrobial mechanism of metal nanoparticles.

Objective: To estimate the prevalence of hepatitis B and C among blood donors attending the National Blood Transfusion Center (NBTC) in Baghdad, Iraq from 2006-2009 and to compare the results with previous year's results and results from studies on a normal population, and to identify certain demographic characteristics such as age, gender, and residence of positive cases., Methods: This is a retrospective cross-sectional observational study. Monthly reports from the NBTC during the year 2006-2009 were collected. This study took place at Communicable Disease Control Center (CDC), Baghdad, Iraq in January 2010. Analysis of the reports regarding age, gender, and residence was carried out using Excel 2007., Results: The sample size was 495,648 blood donors. Out of them, only 3258 (0.6%) were positive for hepatitis B and 933 (0.3%) were positive for hepatitis C. The average prevalence of HBsAg was higher in men (0.7%) than women (0.5%) with no statistical significance (p=0.07) while the prevalence of anti-HCV was higher in women (0.4%) than in men (0.2%) with statistical significance (p=0.000). Residence distribution of the positive cases for HbsAg and Anti HCV Ab in both genders was found to be higher in urban areas than in rural areas. Regarding age distributions, most of the affected donors were between 20-40 years age., Conclusion: The findings indicate that Baghdad is of low endemicity with hepatitis B and hepatitis C infection. Generally, men are affected more than women and urban areas more than rural areas. Further studies are needed to provide more details about the status of HBV and HCV infection in other provinces of Iraq. Results of these studies could be utilized to determine the most feasible and useful approaches for strengthening prevention and control activities.

Autosomal recessive ataxias are a heterogeneous group of rare disorders characterized by early onset ataxia associated with neurologic, ophthalmologic or systemic signs. The ataxias associated with myoclonus, epilepsy and progressive neurological degeneration are usually included with the progressive myoclonus epilepsies, one of which is Unverricht-Lundborg disease. We identified four siblings with ataxia, juvenile onset progressive action tremor and atonic seizures from a Jordanian family. The mode of inheritance of this syndrome is autosomal recessive. We performed a genome-wide screen for linkage and fine mapped the region that contains the disease locus. The four affected siblings have ataxia noted at the onset of walking with dysarthria and bulbar features, but no cerebellar hypoplasia on MRI. They all developed a fine tremor that progressed to a coarse action tremor, as well as atonic seizures. Treatment with valproate fully controlled the seizures and improved the tremor, but did not change the course of the ataxia. We mapped the gene responsible for this disorder to the pericentromeric region of chromosome 12. A recently described autosomal recessive variant of Unverricht-Lundborg disease also maps to the same region. We discuss the similarities and differences between our family and the family with the Unverricht-Lundborg disease variant.