Abstract
Mannitol and trehalose were the predominant soluble carbohydrates in Euglena gracilis strain z growing heterotrophically in complete darkness or in light. The ratio of trehalose to mannitol was correlated with the water activity of the medium. That is, extracts of Euglena gracilis adapted to grow in media supplemented with either sodium chloride or glucose, thereby reducing the water activity, yielded molar ratios of trehalose to mannitol 10 times greater than extracts of cultures grown under conditions in common usage.