What this work is about, in plain words
How can one quickly estimate how much biomass a culture of the red alga Porphyridium contains? The authors related the optical density of the suspension to the dry weight of the cells and obtained a simple formula for a rapid estimate.
Culture density is most conveniently estimated from optical density: the measurement takes minutes. But the red alga Porphyridium purpureum poses a difficulty. Its cells release large amounts of mucous polysaccharides into the medium, which change the optical properties and viscosity of the suspension, so published relationships are contradictory. The authors set out to develop a rapid method for estimating the biomass of this alga from optical density on a common laboratory instrument.
The culture was grown in the laboratory in batches. In each sample, the optical density at 750 nm and the wet and dry weight of the cells were measured in parallel.
According to the authors, optical density and dry weight are linearly related, and a simple formula was obtained for converting one into the other. The authors also found a pitfall: the instrument's readings depend on the position of the cuvette in the holder and can differ almost twofold. The reason is that the instrument measures not only absorption but also light scattering.
The work provides a quick way to monitor culture growth, which is especially important in large installations, where measurement errors multiply.
Limitations. The formula was obtained for one species, one instrument and laboratory conditions. For other conditions, it needs to be checked.