Levels of trehalose and glycogen in <i>Frankia</i> sp. HFPArI3 (Actinomycetales)

Abstract

The levels of soluble trehalose were compared in Frankia sp. ArI3 under various conditions in batch culture. Trehalose appears to be a specialized carbon reserve which is synthesized upon transfer of cultures to fresh medium; thereafter it is metabolized and broken down. Levels reach a peak of 10–20% cell dry weight depending on cultural conditions, then drop to a minimum of 1–2% cell dry weight. A similar pattern is observed whether cells are grown in a medium containing NH 4 Cl or in a medium lacking nitrogen substrates; however, the total levels of trehalose are higher in the latter. The levels of endogenous trehalose showed an inverse correlation with a sharp increase in nitrogenase activity. When cells were inoculated into a medium lacking nitrogen to induce fixation of atmospheric nitrogen, trehalose levels reached their peak in 4 days. The nitrogenase activity (measured with the acetylene reduction technique) increased sharply on the 4th to 5th day. Trehalose levels fell sharply from day 4 to day 5; when they fell to half their maximum, nitrogenase activity decreased sharply. Thereafter, the decline in trehalose concentration paralleled that of nitrogenase activity. When cells were washed free of exogenous carbon, the endogenous trehalose levels dropped to half the initial value in 1 h. The cells continued to respire for 2 days on endogenous reserves. In addition to trehalose, glycogen reserves were extracted from Frankia. At its maximum, the glycogen totalled approximately 10% of the dry weight of cultures grown on a medium supplemented with NH 4 Cl as exogenous nitrogen source, and decreased to ca. 1.0% dry weight in starved cultures. Glycogen did not accumulate significantly in cultures that were induced to fix nitrogen.