PGPR interplay with rhizosphere communities and effect on plant growth and health

Plant roots are colonised by specific and diverse bacterial communities, which fulfil important functions for their host. They are involved in growth promotion as well as pathogen defence. Plant growth-promoting rhizobacteria (PGPR) can be used as sustainable inoculants in agrobiotechnology. In contrast, several PGPR have shown to be opportunistic pathogens in humans. Assessing the pathogenic potential against humans is necessary at an early stage of product development. For this, a microtitre plate assay with Caenorhabditis elegans can be used as fast indicator of potential pathogenicity. Although originating from plant-associated microenvironments themselves, PGPR, if applied to plants in adequate numbers, may perturb indigenous microbial populations and the important ecological functions associated therewith. Therefore, possible non-target effects of the applied antagonists on ecologically important soil-microbes need to be considered. Methods as well as examples from literature and own research are summarised. Altogether, after PGPR treatment only short-term transient effects on the rhizosphere-associated microbial communities were monitored.