Protectants used in the cryopreservation of microorganisms. Author information: 1Medical Zoology.The cryoprotective additives CPAs used in the frozen storage of microorganisms viruses, bacteria, fungi, algae, and protozoa include a variety of simple and.ABSTRACT The cryoprotective additives CPAs used in the frozen storage of microorganisms viruses, bacteria, fungi, algae, and protozoa include a...