Phyllobacterium brassicacearum STM196, a plant growth-promoting rhizobacterium isolated from roots of oilseed rape, stimulates Arabidopsis growth. We have previously shown that the NRT2.5 and NRT2.6 genes are required for this growth promotion response. Since these genes are members of the NRT2 family of nitrate transporters, the nitrogen assimilatory pathway could be involved in growth promotion by STM196. We address this hypothesis using two nitrate reductase mutants, G5 deleted in the major nitrate reductase gene NIA2 and G′4-3 altered in both NIA1 and NIA2 genes. Both mutants had a reduced growth rate and STM196 failed to increase their biomass production on a medium containing NO₃⁻ as the sole nitrogen source. However, they both displayed similar growth promotion by STM196 when grown on an NH₄⁺ medium. STM196 was able to stimulate lateral roots development of the mutants under both nutrition conditions. Altogether, our results indicate that the nitrate assimilatory metabolism is not a primary target of STM196 interaction and is not involved in the root developmental response. The NIA1 transcript level was reduced in the shoots of nrt2.5 and nrt2.6 mutants suggesting a role for this nitrate reductase isoform independently from its role in nitrate assimilation.

The growth response of durum wheat (Triticum durum) to inoculation by two rhisospheric rhizobacteria: Azospirillum brasilense and Bacillus subtilis was evaluated using four ways of inoculation to determine the best method that gives better results. The two rhizobacteria were inoculated on LB liquid medium. Durum wheat was inoculated twice. For the first inoculation, part of the germinated seeds was directly sown on the ground and inoculated by bacterial pellet (PP) or by medium containing bacterial culture (MM). As for the other part of the germinated seeds, they were first immerged for 45 min in a medium containing the bacterial culture, after that, they were sown on the ground. For the second inoculation, it was carried out 10 days after sowing, by the same method, except for the seeds being immerged in the culture medium, which were inoculated this time by bacterial pellet (IP) or by medium containing bacterial culture (IM). After 3 weeks of growth, different plant parameters such as the fresh and dry weight of leaves and roots, the number of leaves, the length of leaves and roots and the chlorophyll levels were compared between inoculated and non-inoculated plants and according to the different inoculation methods. The results demonstrated that the inoculation of durum wheat with these two strains stimulated the growth of the plant, some parameters gave similar effects between the two bacteria and other parameters gave different effects. Similarly, the type of inoculation influenced the response of the plant to the bacterium; some types gave better results compared to others.

Rhizobacteria play an important role in maintaining soil balance. Among these bacteria, there are those taht have shown their ability to promote the growth of plants, known as Plant Growth Promoting Rhizobacteria (PGPR). In our work, we are interested in characterizing 110 bacterial strains isolated in the field in the region of Ben Badis (Constantine Algeria) from 5 varieties of faba bean. Phenotypic and biochemical characterization showed that most of the isolates are cream-colored, slightly raised, flat and opaque, Gram−, catalase+ and oxidase−, and Bacillus form. PCA analysis allowed us to select 40 isolates with a high degree of variability to continue our work. The results obtained have directed us towards different taxonomic groups (rhizobium, Pseudomonas, Bacillus etc.). The evaluation of the PGPR potential of bacteria (phytostimulation, biofertilization and biocontrol), showed that 100% of bacteria are able to produce auxin at different concentrations, with the highest concentration (177.77 µg/mL) for the isolate 6, and that more than 50% of isolates are capable of producing nitrogen, ammonia and phytate mineralization. These PGPR traits have a direct effect on plant growth of five varieties of the faba bean and can be used to select the best performing bacteria for inoculation tests.