Beijerinckia derxii releases plant growth regulators and amino acids in synthetic media independent of nitrogenase activity.

AIMS This study aims at evaluating the ability of Beijerinckia derxii, a free-living nitrogen (N)-fixing bacterium frequently isolated from tropical soils, to release certain plant growth regulators [indoleacetic acid (IAA), ethylene, polyamines] and amino acids into the growth medium. METHODS AND RESULTS The production of those substances was compared using both cultures in which nitrogenase was active (N-free medium) and cultures in which nitrogenase was repressed (combined-N cultures). Those cultures were grown under agitation and in absence of agitation. Total IAA production was higher in agitated, N-free cultures but specific production was greater in combined-N cultures under agitation. Putrescine and spermidine were detected under all conditions tested. Ethylene was produced in both N-free and combined-N cultures. A greatest diversity of amino acids was released in N-free cultures. CONCLUSIONS There was no inhibition of the production of the analysed substances under conditions where nitrogenase was inactive. SIGNIFICANCE AND IMPACT OF THE STUDY Beijerinckia derxii is potentially a producer of plant-active substances; its presence in the natural environment suggests that this bacterium may contribute to the development of other living organisms.