Detecting surfactant-producing microorganisms by the drop-collapse test

A rapid method, 'drop-collapse', was used for screening biosurfactant production by Pseudomonas aeruginosa, Bacillus subtilis, Candida albicans and Phanerochaete chrysosporium liquid cultures. Before measuring the total biosurfactant, the drop-collapse method was used in order to detect rhamnolipid presence in the culture broths. The method was performed in a microwell plate; the polystyrene platform with small wells. If the culture broth contained biosurfactant, the droplets of the broth in the oil-coated wells collapsed. If not, there was no change in the shape of the droplets. Pseudomonas aeruginosa and Bacillus subtilis culture supernatants showed spreading movement, meaning that they produced biosurfactants. However, Candida albicans and Phanerochaete chrysosporium supernatants remained beaded, meaning they did not produce any type of microbial surfactant.