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

Mechanical, Thermal Properties and Stability of Rigid Polyurethane Foams Produced with Crude-Glycerol Derived Biomass Biopolyols

Rigid polyurethane foams of significant renewable content (up to 50%) were produced using biomass biopolyols obtained previously via crude-glycerol mediated solvothermal liquefaction of three industrial biomass residue feedstocks: digested sewage sludge, hemp stalk hurds and sugar beet pulp (DSS, HSH and SBP), and commercial diphenylmethane diisocyanate. The produced foams exhibited higher apparent densities 43–160 kg/m3 and compressive strengths 34–254 kPa compared to tested commercial analogues. Varying foam formulation isocyanate-to-hydroxyl group ratios and blending biomass biopolyols with blank crude glycerol biopolyols led to lighter and less strong products. Blank crude glycerol and DSS biopolyol foams exhibited slowest water absorption rates. Biopolyol foams exhibited higher thermal stability and the non-flame retarded foams showed lower potential for fire spread due to lower pyrolysis gas combustion heat release rates and total released amounts of heat. In terms of fire toxicity, biopolyol foams are suspected to be slightly less toxic than typical commercial PU rigid foams (CO and HCN yields of 172.2 and 6.19 mg/g, respectively), still generating significant amounts of irritant smoke in under-ventilated flaming fire scenarios. The products were stable dimensionally (below 1% elongation) and moderately biodegradable (specific rates of 0.25–0.53%/month). Overall, the foams produced show promise as sustainable alternatives in applications such as domestic construction filler foams, where low density is not crucial but fire safety is of utmost importance