Plant growth-promoting (PGPR) bacteria are beneficial soil bacteria that enhance plant growth against biotic and abiotic stress. Numerous studies have been carried out over the past three decades on the isolation and characterization of rhizospheric bacteria. However, no studies have been conducted on the bacteria present in the rhizosphere of the wild legume plant Chamacytisus ruthenicus when growing in chalky soil. The purpose of this study was to evaluate the abundance of culturable bacteria, assess the morphology of the bacterial cells, profile the chalky soil bacterial community, and characterize its ability to stimulate plant growth. Three soil samples were collected in January at a temperature of 2–4 °C. The first sample was taken from the topsoil, the second sample from the soil 15 cm beneath the surface, and the third sample from the rhizosphere. The results of the study revealed that the abundances of bacteria in the first, second, and third soil samples were 4.25 × 10⁸ cfu/g, 3.58 × 10⁸ cfu/g, and 10.1 × 10⁷ cfu/g, respectively. Furthermore, a total of 23 rhizospheric bacteria were isolated based on differences in their morphological characteristics. The 16S rRNA soil profiling result showed that bacteria belonging to Proteobacteria, Actinobacteria, Gemmatimonadetes, Acidobacteria, and Bacteroidetes were the most dominant groups in the community. Six bacterial isolates (Z10, Z11, Z12, Z15, Z26, and Z44) were chosen to examine the inhibition effects on phytopathogenic microbes and their ability to promote plant growth. The bacterial isolates Z11 and Z15 showed good inhibition against all tested phytopathogenic fungi, while bacterial isolates Z10, Z12, Z15, Z26, and Z44 showed stimulatory effects on the length and fresh weight of the shoots and roots of wheat, maize, and oat seeds. In conclusion, the present study is the first report of chalky soil-associated bacteria found in the rhizosphere of the wild legume plant in the Belgorod region of Russia.

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. In total, seven out of them were reported for their potential effect on plant growth. However, the identification and further characterization of those chalky soil bacteria have not been completed yet. Therefore, the purpose of the present study is 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, antibiotic sensitivity or resistance status, and their effect on plant growth. Moreover, 16S rRNA gene sequencing was used to identify those potent bacterial isolates. The results of the present study demonstrate that all bacterial isolates obtained stable morphology in the three types of growth media. However, four bacterial isolates (Z11, Z12, Z15 and Z44) showed color change. The antibiotic test result also revealed that all the tested bacterial isolates except Z11 and Z24 were resistant to both ampicillin (10 μg) and oxacillin (1 μg), whereas 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 the growth stimulation effect revealed that few bacterial isolates had a stimulation effect on the germination rate of oats and lentils, on the shoot length of maize and oats, on the root length of wheats, maize and lentils, on the fresh weight of wheats and oats or on the dry weight of oat seeds. Furthermore, the 16S rRNA gene sequence analysis result revealed that the bacterial isolates belonged to Streptomycetes spp. and Jantinobacterium sp. To conclude, the potential chalky soil rhizospheric bacteria have a substantial impact on agriculture and the environment.

The goal of the current investigation was to further identify and characterize the chalky soil bacteria that were isolated from the rhizosphere of three wild legumes. We have already published some information about rhizospheric bacteria in chalky soil. In this study, chalky soil bacterial community, bacterial cell morphology, antibiotic susceptibility, plant growth promoting (PGP) features, and the impact of the bacterial isolate EAE-1 on the growth of five legume plants were all studied. The results of the study showed that rhizospheric bacteria in chalky soil had a variety of morphologies, with the phylum proteobacteria being the most prevalent group. In terms of how bacteria react to antibiotics, the current findings showed that all the bacterial isolate was susceptible to Amikacin (30 µg), Neomycin (30 µg), and Tobramycin (10 µg ). According to the overall results of antibiotic susuptability, 47% of the bacterial isolates were sensitive, 23% were intermediate sensitive, and 30% were resistant to the antibiotics under investigation. Additionally, rhizospheric bacteria in chalky soil showed characteristics that promoted plant growth. Of the bacterial isolates, approximately 83.3% fixed nitrogen, 55.6% produced IAA with a 2% L-tryptophan supplement, 44.4% solubilized inorganic phosphate, and over 65% produced extracellular enzymes such amylase, protease, lipase and cellulase. Furthermore, the root length of Phaseolus vulgaris, Vigna unguiculata, and Cicer arietinum was significantly affected by the bacterial isolate EAE-1 (p ≤ 0.05). Furthermore, the biocontrol potential of the bacterial isolates demonstrated that 75% of them supressed the growth of Bipolaris sorokiniana F-4006 and 62.5% inhibited the growth of Pythium vexans F-1193, Aspergillus unguis F-1754, and Alternaria brassicola F-1864. The 16S rRNA gene sequencing result revealed that the bacterial isolates showed high similarity to the species belonging to the genera Streptomyces, Janthinobacterium, and Kitasatospora. In conclusion, chalky soil bacteria would be a promising option for biotechnological applications due to their remarkable characteristics.

The current study was carried out to characterize chalky soil bacteria obtained from the rhizosphere of Acacia species growing in Abardae, Maekel Region of Eritrea. This study collected three chalky soil samples from the rhizosphere of Acacia ethibica, Acacia origena, and non-rhizospheric soil. The samples contained 1.42 × 10¹⁰, 5.35 × 10⁹, and 5.68 × 10⁷ cfu/g of culturable bacteria, respectively. A total of 80 bacterial strains were isolated, with ten selected for further study based on their distinct morphology. The researchers examined the cell morphology and the antimicrobial and plant growth-promoting activity of the chosen bacterial isolates. The study’s findings identified that the aerial mycelium of the strain EAE-1 displayed a unique and previously unreported arrangement of hyphae-bearing spores. The antimicrobial test results also showed that bacterial strains EAE-1, EAE-3, EAE-14, EAE-15, EAE-40, and EAO-24 displayed a wide range of antimicrobial activity against the examined phytopathogens. Furthermore, the seed germination result showed that the majority of bacterial strains had a positive effect on wheat growth, with strains EAE-40 and EAO-17 particularly enhancing maize growth. To sum up, the substantial capabilities of these strains position them as promising candidates for biotechnological applications. This study also represents the preliminary analysis of the microbial composition of Eritrean soil.