Aeration requirements of <i>Rhizobium</i> cultures

Abstract

To obtain a high concentration ofRhizobium in broth cultures, the process conditions should be adjusted to the medium and strain used. Oxygen may be a growth-limiting factor if the micro-organism requirements are not satisfied. In this work the process conditions in shake flasks and stirred fermenters were established, based on the oxygen supply rate, in relation to the cell oxygen demand of the variousRhizobium strains used in inoculant preparations. The strains used wereRhizobium meliloti B-36,R. phaseoli F-10,R. trifolii A-22,Rhizobium spp. LL-22,R-leguminosarum D-91 andR. japonicum 5019. They had maximum oxygen demand rates from 135 to 360 ml O2/l/h in media containing 10 g of carbon source/l, 4 g of yeast extract/l and mineral salts. When the operations were conducted in Erlenmeyer flasks with a volume liquid/volume flask of 0.150 in a rotary shaker at 250 rev/min and 2.5 cm eccentricity, the oxygen absorption rate was 355 ml O2/l/h. In mechanically stirred fermenters with a liquid depth/fermenter diameter of 1, with an agitation rate of 250 to 450 rev/min and an air flow rate of 0.5 v/v/min, the bacteria had oxygen absorption rates of between 233 and 661 ml O2/l/h. These conditions allowed the attainment of 1.2 to 2.4×1010 viable cells/ml from between 24 and 72 h.