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

Recent advances and future directions in soils and sediments research

In 2010, the Journal of Soils and Sediments (JSS) reached a milestone: its 10th anniversary. This prompted us to think about where the academic community has come in its understanding of the behaviour of soils and sediments within landscapes. The rapid growth of the journal and the number of papers published in it, and other related journals, suggests, probably correctly, that there is much interest in the topics of soils and sediments. In the January 2011 editorial (Xu and Owens 2011), we presented an overview of some of the main developments in the past 10 years and provided some future directions of JSS for 2011 and beyond. In that editorial we indicated that a more comprehensive editorial would be published in the journal on the recent advances and future directions of soils and sediments research. The following sections are presented to fulfill this commitment and start a dialogue with the journal subject editors, authors and readers in these important areas of soils and sediments research. The dawn of the next decade of JSS is a good time to reflect on progress to-date and, more importantly, to consider where research needs to go in the years ahead; a time of rapid environment change, a time of rapid population growth, and a time when society is increasingly looking to science to provide the understanding (and solutions) to the problems that we face.No Full Tex

Author Correction: Robust estimation of bacterial cell count from optical density

An amendment to this paper has been published and can be accessed via a link at the top of the paper.</jats:p

Robust estimation of bacterial cell count from optical density

AbstractOptical 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  &lt;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.</jats:p