Semipurification and characterization of Antifreeze protein from the Arctic Bacterium Aquaspirillum sp. KOPRI-AB30

Abstract

Antifreeze proteins (AFPs) bind to the surface of ice crystals and control ice crystal structure. They have thermal hysteresis (TH) activity, which is the non-colligative depression of the freezing point by inhibiting the growth of ice crystal. We isolated some bacteria capable of producing antifreeze proteins as part of cold adaptation mechanism from the Arctic. Among these, the strain KOPRI-AB30 showed high antifreeze activity and was identified as Aquaspirillum sp. The psychrophilic bacterium Aquaspirillum sp. KOPRI-AB30 produced antifreeze protein extracellularly. The optimal temperature and pH for the production of AFP were 5℃ and 7.0, respectively. The AFP was partially purified from the culture supernatant with tangential flow filtration and subsequent chromatography. Molecular mass of the partially-purified AFP was approximately 30 kDa. The ice-crystal controlling activity of the AFP was observed using nanolitre osmometer. The thermal hysteresis of the protein was determined to be about 0.7℃. In addition, the AFP is relatively heat and pH stable, but not calcium dependant. The possible use of the protein as a cryoprotectant was also tested.