Plant growth-promoting rhizobacteria represent a promising solution to enhancing agricultural productivity. Here, we screened phosphate solubilizing bacteria from the rhizospheric soil of Chenopodium quinoa Willd and assessed their plant-growth promoting rhizobacteria (PGPR) properties including production of indole-3-acetic acid (IAA), siderophores, hydrogen cyanide (HCN), ammonia and extracellular enzymes. We also investigated their tolerance to salt stress and their capacity to form biofilms. Two isolated strains, named QA1 and QF11, solubilized phosphate up to 346 mg/L, produced IAA up to 795.31 µg/mL, and tolerated up to 2 M NaCl in vitro. 16S rRNA and Cpn60 gene sequencing revealed that QA1 and QF11 belong to the genus Bacillus licheniformis and Enterobacter asburiae, respectively. In vivo, early plant growth potential showed that quinoa seeds inoculated either with QA1 or QF11 displayed higher germination rates and increased seedling growth. Under saline irrigation conditions, QA1 enhanced plant development/growth. Inoculation with QA1 increased leaf chlorophyll content index, enhanced P and K+ uptake and decreased plant Na+ uptake. Likewise, plants inoculated with QF11 strain accumulated more K+ and had reduced Na+ content. Collectively, our findings support the use of QA1 and QF11 as potential biofertilizers.

In order to evaluate the suitability of 16S rRNA nucleotide sequence similarity for the classification of new Mycobacterium isolates at the species level, we systematically studied the pairwise identity values of this gene for 131 Mycobacterium species with standing in nomenclature. Only one of the studied species, M. poriferae (0.76%), strictly respected the 95% and 98.65% threshold values currently recommended to determine the affiliation of bacterial isolates to an existing or new genus or species, respectively. All other species exhibited at least an identity value >98.65% and/or <95% with another Mycobacterium species. Therefore, we suggest that interpretation of interspecies 16S rRNA identity values should be made cautiously when classifying a new mycobacterial isolate at the species level.

In recent years, the low Zn content of wheat has become critical. Consequently, solutions that can improve the Zn nutrition of wheat are highly researched. In the present investigation, we aimed to evaluate the potential benefits of phosphate-solubilizing bacteria isolated from Ziziphus lotus on wheat seedling growth. Based on the phosphate-solubilizing criteria, four isolated strains, J16, J143, J146, and J158, were identified by 16SrRNA gene sequencing as Pseudomonas moraviensis, Bacillus halotolerans, Enterobacter hormaechei, and Pseudomonas frederiksbergensis, respectively. Studies of the conventional properties of plant growth-promoting rhizobacteria (PGPR) showed that E. hormaechei J146 produced up to 550 mg·L−1 of indole-3-acetic acid (IAA). Siderophores and ammonia were produced by all strains but cellulase was restricted to B. halotolerans J143, whereas proteases were missing in E. hormaechei J146 and P. frederiksbergensis J158. E. hormaechei J146 tolerate up to 1.5 mg·L−1 of copper and cadmium, while B. halotolerans J143 withstood 1.5 mg·L−1 of nickel. Strains B. halotolerant J143, E. hormaechei J146, and P. frederiksbergensis J158 remarkably improved wheat seed germination, plant growth, and Zn absorption. Lastly, nutrient measurement revealed that a wheat plant inoculated with E. hormaechei J146 and P. frederiksbergensis J158 increased its nitrogen and potassium uptake by up to 17%.