Robust estimation of bacterial cell count from optical density

Optical density (OD) is widely used to estimate the density of cells in liquid culture, but cannot be compared between instruments without a standardized calibration protocol and is challenging to relate to actual cell count. We address this with an interlaboratory study comparing three simple, low-cost, and highly accessible OD calibration protocols across 244 laboratories, applied to eight strains of constitutive GFP-expressing E. coli. Based on our results, we recommend calibrating OD to estimated cell count using serial dilution of silica microspheres, which produces highly precise calibration (95.5% of residuals <1.2-fold), is easily assessed for quality control, also assesses instrument effective linear range, and can be combined with fluorescence calibration to obtain units of Molecules of Equivalent Fluorescein (MEFL) per cell, allowing direct comparison and data fusion with flow cytometry measurements: in our study, fluorescence per cell measurements showed only a 1.07-fold mean difference between plate reader and flow cytometry data

Migration and Development: The Policies of China and India with regard to their Overseas Communities

Published by Palgrave MacmillanFocusing on India and China, two countries with high levels of emigration that have developed policies aimed at promoting ties with their nationals who live abroad, this article contributes to the academic and political debate about the relationships between the phenomenon of migration and the development of migrants’ countries of origin. In light of the measures that both these countries have amassed for the benefit of their overseas communities, one can identify the need to create one or more institutional structures to promote individual initiatives. The importance of reciprocity is emphasised, which is an essential aspect of relations between the government of the country of origin and its migrants