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

Introduction: Animals, Place and Humans

Place has multispecies meaning. From their wintering grounds in Central America individual Wood Thrushes (Hylocichla mustelina) have been shown to return over 7500 km to the same place they nested the year before (Stutchbury et al.). With this example, one among many, it is clear that humans are not the only species to have a relationship to place. Just as it has been shown that humans are not the sole proprietors of language and culture (Rendell and Whitehead; Pepperberg and Lynn), place is another fertile territory to disrupt our human-held assumptions about animal