INTERACTIONS BETWEEN RHIZOSPHERE MICROORGANISMS UNDER IRON LIMITATION

Bacillus polymyxa, Pseudomonas cepacia and Pseudomonas fluorescens are present in the rhizosphere of many crop plants. Little is known about microbial interactions in the rhizosphere. We investigated the type o f interaction between these species under iron limitation. We found th at, in mixed batch cultures, P. cepacia stimulates the growth of B. po lymyxa and this stimulation can be observed also in low iron medium. C ell-free supernatants of cultures of P.fluorescens with various amount s of the siderophore pyoverdine also stimulate the growth of B. polymy xa. In this case we observed a positive correlation between pyoverdine concentration and growth stimulation. Purified pyoverdine also affect s positively the growth of B. polymyxa.