Growth behaviour and IAA production by a Rhizobium sp. isolated from root nodules of a leguminous medicinal herb, Tephrosea purpurea Pers., in culture

Abstract

The Rhizobium sp. isolated from the root nodules of a leguminous medicinal herb, Tephrosea purpurea Pers. produced a high amount of indole acetic acid (126 μg/ml) from L-tryptophan supplemented basal medium. Growth and indole acetic acid production started simultaneously, the bacteria had a separate growth and production phase. The production was maximum in the stationary phase of growth of the bacteria. Attempts were made to optimize the cultural requirements for the growth and maximal IAA production. The IAA production by the Rhizobium sp. was increased by 487.5% when the medium was supplemented with sucrose (1%), NiCl 2, 6 H 2O (2 μg/ml), nicotinic acid (1.5 μg/ml), cetyl pyridium chloride (1 μg/ml) and KNO 3 (0.2%). The possible role of the rhizobial production of indole acetic acid on the Rhizobium — legume symbiosis is discussed.