Identification of plant growth promoting bacteria of Noccaea birolmutlui and Bornmuellera kiyakii endemic plants

Chemical fertilisers, population growth, water requirements and stressful soil conditions make it increasingly difficult to increase crop yields. Some plant species can thrive under stressful conditions. For example, in serpentine (ultramafic) soils with inadequete nutrients and high levels of heavy metals such as chromium, nickel and aluminium, hyperaccumulator plants thrive and cope well with harsh environmental conditions. Hyperaccumulator plants have the ability to survive by accumulating heavy metals in above-ground organs. Plant Growth Promoting Bacteria (PGPB), found in the rhizosphere of plants and as endophytes, have mechanisms that promote plant growth and reduce the phytotoxic effects of heavy metals by forming a symbiotic relationship with plants. PGPB have many functions that support plant development, such as production of antibiotics against soil-borne diseases, nitrogen fixation, phosphate dissolution, production of siderophores, production of hormones such as indole acetic acid (IAA), and production of 1-aminocyclopropane-1-carboxylate (ACC) deaminase, and reduction of the amount of ethylene that increases under stress conditions. Thanks to these functions, the use of PGPB in agriculture is considered a better alternative to the conventional approach to increase crop yield and quality. The isolation and use of PGPB is an environmentally friendly approach that promotes productivity, efficiency and food quality in the face of increasing food demand. In this study, endophytes and rhizobacteria that promote plant growth were isolated from endemic hyperaccumulator plants Noccaea birolmutlui Özgişi & Özüdogru and Bornmuellera kiyakii Aytaç & Aksoy. The production of ACC deaminase and siderophores, phosphate solubility and indole acetic acid (IAA) activity, and heavy metal and antibiotic resistance of PGPB properties of the isolated bacteria were investigated. These bacteria were found to be resistant to heavy metals such as lead, zinc, copper, nickel, aluminium and chromium, and most of these bacteria developed inhibition zones against the antibiotics tetracycline, chloramphenicol, kanamycin and imipenem. As a result of the studies, all tests were evaluated independently and 38 bacterial strains with the best PGPB activity were selected. The 16S rRNA gene region, which is important for bacterial systematics, was chosen as the target gene region for their molecular identification. As a result of the identification, the bacteria were found to belong to the genera Achromobacter, Acinetobacter, Microbacterium, Pantoea, Pseudomonas and Priestia.