Quantitative real time measurements of bacteria–bacteriophages interactions in fresh lettuce leaves

Bacteriophages are promising bactericidal agents for controlling growth of pathogenic and spoilage bacteria in fresh produce and in minimally-processed food. However, there is a lack of quantitative understanding of phage–bacteria interactions within a food matrix. To address this unmet need, the interactions of lytic bacteriophages with target model bacteria on the surface and interior (infiltrated) of a fresh produce were characterized using bioluminescence spectroscopy and imaging approaches. The results showed that the phages applied to the surface of lettuce leaves effectively reduced the level of bacterial targets that were present both on the surface and inside of lettuce leaves. However, there were significant differences in the initial rate of decrease of bacteria in the three model systems examined in this study: (a) homogenous well-mixed solution, (b) inoculated on the surface, and (c) infiltrated into the interior of lettuce leaves. The results also demonstrate the application of bioluminescence imaging for non-invasive measurement of interactions between bactericidal agents and target pathogens over an extended period of time in lettuce samples. The number of bacterial cells in lettuce samples before and after phage treatment predicted based on bioluminescence measurements was in agreement with the number calculated by conventional plate counting methods. In summary, the results highlight a non-invasive real-time imaging approach to quantitatively measure interactions of bacteriophages with both the surface inoculated and the infiltrated model bacterial cells in leafy greens.     

Dream Bloggers Invent the University

This essay focuses on the blogs authored by students in interdisciplinary, writing-intensive seminars on the art and science of dreaming at Queens College and Princeton University. The writing for these courses requires students to “invent the university” in the sense that they must find ways to bridge the public and private, or the theoretical and the personal. I argue that blogs have the potential to help students develop strong and distinctive voices in the pursuit of intellectual inquiry—and that because of this, they can help teachers and scholars overcome the intellectual divides between the “expressivist” and “constructivist” pedagogies represented by Peter Elbow and David Bartholomae respectively. In the concluding section, I examine blog entries in which students recount instances in which they dreamed about our course readings (and other materials). These accounts are striking because they offer evidence that students were internalizing and synthesizing course material. To explain this internalization and synthesis, I turn to recent developments in cognitive theory that offer new ways of thinking about learning that I believe will help bridge the expressivist-constructivist divide and develop methods for teaching voice as a rhetorical element of writing, one that is essential to intellectual inquiry.     

Simple quantitative analysis of Escherichia coli K-12 internalized in baby spinach using Fourier Transform Infrared spectroscopy

Bacterial contamination continues to be a serious concern for food safety. Although washing fresh produce helps in reducing pathogen levels, pathogen internalization often limits the effectiveness of washing. When pathogens internalize in leafy vegetables, the method of identification and quantitative measurement would be called into question. This study was aimed to use Fourier Transform Infrared (FTIR) spectroscopy integrated with an attenuated total reflectance kit for quantification of Escherichia coli K-12 internalized in baby spinach. The bacteria were inoculated into vascular and intracellar tissues of spinach leaves by syringe injection and the distribution of internalized E. coli K-12 cells was confirmed under scanning electron microscopy (SEM). FTIR measurement following the preparation of bacterial suspension from spinach leaves with high speed pulverizing enabled to detect the absorbance peaks in the amide II region between 1590 and 1490 cm⁻¹ as a fingerprint for the microbes. It was found that the estimated concentrations of E. coli K-12 agreed well with the concentrations determined by plate counting with R² values of 0.98 and 0.97 in peptone water and spinach extracts, respectively. The results demonstrated that FTIR can identify and quantify E. coli K-12 in baby spinach extracts at a limit of detection of approximately 100 CFU/mL in 5 min. The developed method is expected to be suitable for the analysis of pathogenic E. coli strains and other bacterial species in fresh vegetables.     

Comparison of nitrification inhibition by metals in batch and continuous flow reactors

Stringent effluent discharge limits for nitrogen require development of assays to accurately and rapidly determine whether a wastewater stream will inhibit nitrification. The suitability of a short-term extant batch respirometric assay to predict nitrification inhibition by metals (Cu, Zn, Ni and Cd) in continuous flow reactors was evaluated. Linear metal partition coefficients were determined to be 78.42+/-2.46, 0.54+/-0.04, 0.05+/-0.01 and 0.60+/-0.01 L/g biomass COD in batch experiments (pH=7.5) for Cu, Zn, Ni and Cd, respectively. A mass-balance model, incorporating metal partitioning, adequately fit the metal concentration profiles in the continuous flow reactor during and after a 24-hour shock load. However, the short-term batch assays significantly underestimated observed inhibition in the continuous flow reactor. The underestimation was, most likely, due to slow kinetics of Zn, Ni and Cd internalization and an exacerbation effect due to continued metal exposure in the continuous flow reactor. The discrepancy in inhibition between batch and continuous systems was the largest for Cu, presumably due to its unique mode of action, which involves loss of cell membrane integrity. Hence, using results from short-term batch respirometric assays to infer responses in continuous flow reactors with longer exposure should be done with caution and must accommodate partitioning behavior and internalization kinetics.     

风物之间,内化的江南 上海青浦练塘镇政府办公楼设计策略分析

文章通过分析上海青浦练塘镇政府项目的设计策略,探讨对传统江南建筑内在结构的继承与更新以及地方建筑特征的内化。     

What type of information displayed on digital scheduling software facilitates reflective planning tasks for students? Contributions to the design of a school task management tool

To facilitate an efficient homework planning strategy, scheduling software tools should take students’ needs into consideration, in order to provide information that is useful for planning homework and that minimizes cognitive load.     

Translocation and transformation of engineered nanomaterials in plant cells and their effect on metabolism

As the climate worsens and the demand for food grows, so does the interest in nanoagriculture. The interaction between plants and nanomaterials (NMs) has been extensively and intensively examined. However, stopping at the outcome of a phenomenon is often insufficient. Therefore, we introduce three important processes of nanoparticle-plant interactions: translocation, transformation, and plant metabolism. During the migration of nanoparticles, size and surface electrical properties are the main determining factors. Additionally, the interaction of nanoparticles with cell membranes is another key aspect of research. The transformation of nanoparticles in plants is mainly due to redox substances. The way that nanoparticles affect plant metabolism may be able to shed light on the interaction of nanoparticles with plants. This review adds to the existing knowledge on the design of nanoagrochemicals and summarizes the mechanism of interaction of NMs with plants. In this way, NMs can be used for their beneficial effects and thus contribute to the maintenance of food security and sustainable development.