Dry cell weight for Κ

The dry cell weight method is simple. A well-defined volume of the culture is filtered and the sample is dried in an oven and placed in a desiccator before the weight is determined. The filter will retain large objects like cells, but allow smaller substances to pass through

Determination of cell dry weight by filtration, drying and weighing.

Advantages of dry cell weight for K

Main advantages of dry cell weight is that it is simple and robust. It requires only very basic tools and is a well-established method for biomass determination.

Unlike optical density, cell dry weight does not depend strongly on cell shape or refractive properties. In addition the method is less influenced by optical artifacts like colored media and pigment formation.

Disadvantages of dry cell weight for K

Concerning disadvantages, dry cell weight has low throughput and is not a real-time method. For frequent sampling, this is not the method of choice.

Calibration factors are needed to convert dry cell weight to cell concentrations and therefore the method has the same pitfalls as the optical methods. For instance, the calibration factors depend on the size of the objects.The industry standard is to apply a single calibration factor for each species, despite potential variations across growth phases and media.

Analogous to the optical methods, dry cell weight does not distinguish between bacterial and non-bacterial objects.

Practical recommendations

Cell dry weight has shortcomings for screening of carrying capacity, Κ. Calibration factors will depend on growth phases and media and therefore wrong decisions may result if based on cell dry weight. Also note that cell dry weight may include other particulates larger than the pores of the filters.

Nonetheless there are special cases where cell dry weight may be the best method. Some cells like Actinomyces and Bacillus species are especially prone to filamentation and/or clumping. In these cases, the dry weight is a robust method for quantifying the total biomass.

If you are more interested in the metabolic capacity than the carrying capacity, then the cell dry weight might also be more fit-for-purpose than alternative methods.