A dye binding method for measurement of total protein in microalgae

Protein is a large component of the standing biomass of algae. The total protein content of algae is difficult to measure because of the problems encountered in extracting all of the protein from the cells. Here we modified an existing protein assay to measure total protein in microalgae cells that involves little or no extraction of protein from the cells. Aliquots of fresh or pretreated cells were spotted onto filter paper strips. After drying, the strips were stained in a 0.1% (w/v) solution of the protein stain Coomassie Brilliant Blue R-250 for 16 to 24 h and then destained. The stained protein spots were cut out from the paper, and dye was eluted in 1% (w/v) sodium dodecyl sulfate (SDS). Absorbance at 600 nm was directly proportional to protein concentration. Cells that were recalcitrant to taking up the dye could be either heated at 80°C for 10 min in 1% SDS or briefly sonicated for 3 min to facilitate penetration of the dye into the cells. Total protein measured in Chlorella vulgaris using this method compared closely with that measured using the total N method. Total protein concentrations were measured successfully in 12 algal species using this dye binding method.