The effect of the temperature of growth on the polysaccharide content of Bact. lactis aerogenes

Abstract

The levels of polysaccharide per unit of mass in a salts-glucose medium at 25, 37 and 42 °C are not very different and show in general a drop in the early part of the growth cycle (like DNA /mass) followed by a slower rise (unlike DNA /mass). If the content of ammonium sulphate in the medium is reduced so that its exhaustion limits growth, much higher levels are obtained at 25 and 37 °C and reach a maximum 24 h after inoculation. At 42 °C the synthesis of ‘excess’ polysaccharide is impaired and the increase is much less marked. Keeping the pH constant at 7-1 increases the polysaccharide content of the culture at 37 °C, but makes little difference at 25 or 42 °C. The ‘excess’ polysaccharide is not readily utilized as a sole source of carbon in a succeeding cycle and results are presented which suggest that it is not as much a reserve as a consequence of an abnormal metabolism from which the cells eventually recover. In this abnormal metabolism it is better to regard the entire bacterial culture as an integrated community since it is difficult to decide, except in an arbitrary manner, how much of the ‘excess’ polysaccharide is part of the cells and how much is in the medium.