RESUMO
The turbidity of a microbial suspension sample is routinely determined by measuring the optical density (often referred to as the "absorbance"). This method requires a dilution step at moderate and high cell densities in order to ensure that measurements fall within the region where biomass concentration is linearly correlated to optical density. The measurement of backscattered light (often referred to as the "reflectance"), which has so far been mainly applied to large-scale stirred tanks, should also be applicable on the microscale. To evaluate the validity of this assumption, a standard fluorescence microplate reader was adapted to measure backscattered light. Backscattered light readings from undiluted microbial fermentation samples determined using this modified reader gave similar growth curves to optical density measurements from diluted samples determined in a standard cell photometer. Indeed, the fact that the dilution procedure is not necessary for backscattered light measurements gives them an important advantage over optical density measurements. Such an apparatus is not only suitable for manual operation, but also shows the potential for integration into fully automated robotic systems used for high-throughput experimentation.