PRODUCTION OF AUXIN AND OTHER INDOLIC AND PHENOLIC-COMPOUNDS BY PAENIBACILLUS-POLYMYXA STRAINS ISOLATED FROM DIFFERENT PROXIMITY TO PLANT-ROOTS

We determined the actual (no tryptophan, Trp, addition) and potential (Trp 0.1 g l(-1) added) production of indolic and phenolic compounds p roduced in different culture media by Paenibacillus polymyxa strains w hich had been isolated from different proximity to wheat roots. The pr oduction of indole-3-acetic acid (IAA) and related indolic metabolites by all strains tested was greatly enhanced upon Trp addition, suggest ing that Trp is important as IAA precursor. A gradual decrease in pote ntial IAA and an increase in potential indole-3-ethanol and indole-3-l actic acid production by strains isolated from non-rhizosphere soil (N RS) over rhizosphere soil (RS) to the rhizoplane (RP) were obtained. T he NRS strain showed also a higher (potential) production of oxidized compounds such as indole-3-carboxylic and benzoic acid besides IAA. Th e determined metabolic differences indicate together with previous res ults on genetic and physiological parameters of P. polymyxa population s that plant roots select different P. polymyxa subpopulations. Our re sults suggest that the selected genotypes are differentially adapted t o the decreasing oxygen pressure from NRS to RP. Possible effects of t he probably microhabitat-specific metabolic profiles of the P. polymyx a isolates for plant growth are discussed.