producing siderophores that chelate iron and make it available to the plant root; solubilizing minerals such as phosphorus, producing phytohormones and synthesizing some compounds or enzymes that can develop plant growth. Indi-rect growth stimulation of plants is also connected with protectionthem against the effects of phytopathogens. In this case, the bacte-ria compete for space at the root of pathogens, where they producechelators (so-called siderophores) which are specific for the Fe3+ions. Siderophores have a higher affinity for iron than chelators pro-duced by pathogenic microorganisms present in the rhizosphere.Thus, the Fe3+becomes unavailable for pathogens. PGPR bacteriaare also capable of the production of secondary metabolites withantibiotic properties or are antifungal substances, insecticides andimmunosuppressants (Glick, 2005). The PGPR include free-livingsoil bacteria that occur in the root zone and endophytic bacteria,colonizing the root cells. The largest group of PGPR bacteria arePseudomonas, Bacillus, Enterobacter, and Erwinia. Indoleacetic acid(IAA) that is produced by the bacteria may enhance the effects ofplant auxin and can directly affect root growth by stimulating celldivision and elongation of the plant (Kalitkiewicz and K˛epczy´nska,2008). Bacteria associated with the surface roots can capture sep-arated ACC (1-aminocyclopropane-1-carboxylic acid) and by ACCdeaminase activity and convert it to -ketobutyrate and ammonia(Rab˛eda and Wo´zny, 2011). The resulting ammonia from hydroly-sis of ACC is the nitrogen source for the bacteria, which is beneficialwhen the soil is deficient in this element. Moreover, the distribu-tion of ACC leads to inhibition of the synthesis of ethylene in plants.A large group of PGPR bacteria are also diazotroph, i.e. microorgan-isms capable of fixing atmospheric nitrogen. PGPR nitrogen-fixing