Yeast Gets A Protective Coating

Chinese researchers have devised a way to protect yeast cells with a mineral coating similar to an eggshell (Angew. Chem. Int. Ed., DOI: 10.1002/anie.200704718). Such a coating can extend the shelf life of cells during storage. Ruikang Tang and coworkers at Zhejiang University altered the surface properties of the yeast cell with a mixture of polyelectrolytes. The high density of carboxylate groups in one of the polyelectrolytes provides active nucleation sites for the precipitation of calcium phosphate on the cell, which becomes completely encased in the mineral. Encapsulated cells enter a resting state and can be reactivated by dissolving the shell in a pH 5.5 HCl solution. Many of the protected cells remain viable after one month in water. They can also withstand harsh conditions, such as exposure to a mixture of enzymes that would usually digest the cell wall. In both cases about 15% of the cells die, possibly because of defects in the shells.