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

Quantification of the impact of cover crops on Net Ecosystem Exchange using AgriCarbon-EOv0.1

International audienceDetermination of agricultural fields carbon budget is needed to devise the best sustainable agriculture strategies, and quantify future subsidies in the agricultural sector. One major sustainable practice is cover crops that are planted in between main crops cycles, enabling storage of carbon and reduction of reflected heat. Assimilation of Earth Observation data is crucial for such exercise due to the sheer heterogeneity and complexity of crop modeling in the real environment. In this paper, we present the impact of cover crops on Net Ecosystem Exchange (NEE) and Biomass over a large area in the south-west of France using the AgriCarbon-EO. This tool is an end-to-end solution that enables a Bayesian assimilation of multi-temporal and entire tiles (100x100 km) Sentinel-2 reflectance data into a radiative model and a crop model. Our results show an increase of NEE of about due to cover crops over maize fields