Effects of di- and polysaccharide formulations and storage conditions on survival of freeze-dried Sphingobium sp.

In this study we have compared the ability of the organic polymers Ficoll and hydroxyethylcellulose (HEC) and the disaccharides sucrose and trehalose to support cell survival during freeze-drying and subsequent storage of a gram-negative Sphingobium sp. In addition to determination of viability rates, cell integrity was evaluated using lipid peroxidation and RNA quality assays for the different storage conditions and formulation compositions. All formulations resulted in high initial cell survival rates after freeze-drying. However, the disaccharide formulations were superior to the polymer-based formulations in supporting cell survival during storage with the exception of Ficoll that upon storage under vacuum yielded bacterial survival rates equal to that of sucrose. Storage in the presence of both oxygen and moisture was detrimental for bacterial survival in all formulations tested, however, lipid peroxidation or RNA damages were not the controlling mechanisms for cell death in this system. The ability of Ficoll and HEC to support cell survival during freeze-drying show that organic polymers, expected to lack the water replacing capability of e.g. disaccharides, can successfully be used as lyoprotectants. For storage under vacuum conditions we suggest that the intracellular amount of sugars (i.e. trehalose), or other protective native cell components, is sufficient for a basic protection inside the bacteria cell and that the amorphous state is the most important aspect of the formulation excipient. However, when exposed to oxygen and moisture during storage this protection is not sufficient to prevent cell degeneration.