Identification and characterization of potential chalky soil plant growth promoting bacteria (PGPR) isolated from the rhizosphere of Chamaecytisus ruthenicus (Russian broom)

Plant growth-promoting rhizospheric bacteria (PGPR) are well known for their significant roles in agriculture and the environment. In our previous study, 23 chalky soil bacterial isolates were obtained from the rhizosphere of Chamaecytisus ruthenicus. Seven out of them were generally reported for their potential to promote plant growth. However, the identification and further characterization of those chalky soil bacteria were not done yet. Therefore, the purpose of the present study was to identify and characterize chalky soil rhizospheric bacteria (seven previously investigated and one additional bacteria). A total of eight bacterial isolates were cultured in LB and other growth media to investigate their morphological behavior, antibitoic sensitivity or resistance status, and their effect on plant growth. Moreover, 16S rRNA gene sequencing was used to identify such potential bacterial isolates. The results of the present study demonstrated that three bacterial isolates showed morphological variability at various compositions of LB and other growth media. The antibiotic test result also revealed that all the tested bacterial isolates except Z11, Z24, and Z44 were resistant to both ampicillin (10 μg) and oxacillin (1 μg). where as all bacterial isolates were sensitive to polymyxin (300 units), amoxicillin (20 μg), vancomycin (30 μg), ceftazidime (30 μg), erythromycin (15 μg), ciprofloxacin (5 μg), bacitracin (10 units), and streptomycin (30 μg). The result of seed germination showed that bacterial strains Z11, Z12, and Z15 suppressed the root growth of wheat, oats, and lentils. while, Z26 significantly increases the root length of wheat. Furthermore, the 16S rRNA gene sequence analysis result revealed that the bacterial isolates belonged to the Protobacteria, Actinobacteria, Acidobacteria, and Gemmatimonadetes. As a conclusion, such potential chalky soil rhizospheric bacteria would have a substantial impact on agriculture and the environment.