Bradyrhizobium and Pseudomonas strains obtained from coal-mining areas nodulate and promote the growth of Calopogonium muconoides plants used in the reclamation of degraded areas

Screening halotolerant bacteria for their potential as plant growth-promoting and coal-solubilizing agents

The bioconversion of salinized land into healthy agricultural systems by utilizing low-rank coal (LRC) is a strategic approach for sustainable agricultural development. The aims of this study were: (1) to isolate bacterial strains associated with the rhizosphere of native plants in coal-containing soils, (2) to characterize their plant growth-promoting (PGP) and coal-solubilizing capabilities under laboratory conditions and (3) to evaluate their influence on the germination and growth of chia seeds under saline stress. Fourteen bacterial cultures were isolated from the rhizosphere of Artemisia annua L. using culture media containing salt and coal. Based on their PGP activities (nitrogen fixation, phosphate solubilization, siderophore and indole-3-acetic acid production), five strains were selected, belonging to the genera Bacillus, Phyllobacterium, Arthrobacter, and Pseudomonas. Solubilization assays were conducted to confirm the ability of these strains to utilize coal efficiently. Finally, the selected strains were inoculated with chia seeds (Salvia hispanica L.) to evaluate their ameliorating effect under saline stress conditions in coal-containing media. Inoculation with A. subterraneus Y1 resulted in the highest germination and growth metrics of chia seeds. A positive but comparatively weaker response was observed with P. frederiksbergensis AMA1 and B. paramycoides Lb-1 as inoculants. Coal inoculated with halotolerant bacteria can serve as the foundation for humified organic matter in salt-affected environments. The selected halotolerant bacteria enhance coal biotransformation while exhibiting PGP traits.

Impacts of phosphate-solubilizing bacterium strain MWP-1 on vegetation growth, soil characteristics, and microbial communities in the Muli coal mining area, China

Due to the cold climate and low soil nutrient content, high-altitude mining areas are challenging to restore ecologically. Their poor nutrient content may be ameliorated by introducing specific microorganisms into the soil. This study aims to evaluate the effects of a highly efficient phosphate solubilizing bacterium MWP-1, Pseudomonas poae, on plant growth, soil nutrients in remedying the soil of the high-altitude Muli mining area in Qinghai Province, and analyze its impact on microbial communities through high-throughput sequencing soil microbial communities. The results showed that MWP-1 significantly increased the content of soil available phosphorus by >50%, soil organic matter and total nitrogen by >10%, and significantly increased the height, coverage, and aboveground biomass of vegetation by >40% in comparison with the control (p < 0.05). MWP-1 mainly affected the composition of the soil bacterial communities at the taxonomic level below the phylum. Its impact on soil fungal communities occurred at the phylum and below taxonomic levels. In addition, MWP-1 also significantly improved the diversity of soil bacterial and fungal communities (p < 0.05), and changed their functions. It also significantly altered the relative abundance of genes regulating phosphorus absorption and transport, inorganic phosphorus dissolution and organic phosphorus mineralization in the bacterial community (p < 0.05). It caused a significant increase in the relative abundance of the genes regulating nitrogen fixation and nitrification in nitrogen cycling (p < 0.05), but a significant decrease in the genes regulating phospholipase (p < 0.05). Although sequencing results indicated that Pseudomonas poae did not become the dominant species, its dissolved phosphorus elements can promote plant growth and development, enrich soil nutrient content, and affect the succession of microbial communities, enhance ecosystem stability, with an overall positive effect on soil remediation in the mining area.

Is the Application of Plant Probiotic Bacterial Consortia Always Beneficial for Plants? Exploring Synergies between Rhizobial and Non-Rhizobial Bacteria and Their Effects on Agro-Economically Valuable Crops

The overgrowth of human population and the demand for high-quality foods necessitate the search for sustainable alternatives to increase crop production. The use of biofertilizers, mostly based on plant probiotic bacteria (PPB), represents a reliable and eco-friendly solution. This heterogeneous group of bacteria possesses many features with positive effects on plants; however, how these bacteria with each other and with the environment when released into a field has still barely been studied. In this review, we focused on the diversity of root endophytic rhizobial and non-rhizobial bacteria existing within plant root tissues, and also on their potential applications as consortia exerting benefits for plants and the environment. We demonstrated the benefits of using bacterial inoculant consortia instead of single-strain inoculants. We then critically discussed several considerations that farmers, companies, governments, and the scientific community should take into account when a biofertilizer based on those PPBs is proposed, including (i) a proper taxonomic identification, (ii) the characterization of the beneficial features of PPB strains, and (iii) the ecological impacts on plants, environment, and plant/soil microbiomes. Overall, the success of a PPB consortium depends on many factors that must be considered and analyzed before its application as a biofertilizer in an agricultural system.

The extreme plant-growth-promoting properties of Pantoea phytobeneficialis MSR2 revealed by functional and genomic analysis

Numerous Pantoea strains are important because of the benefit they provide in the facilitation of plant growth. However, Pantoea have a high level of genotypic diversity and not much is understood regarding their ability to function in a plant beneficial manner. In the work reported here, the plant growth promotion activities and the genomic properties of the unusual Pantoea phytobeneficialis MSR2 are elaborated, emphasizing the genetic mechanisms involved in plant colonization and growth promotion. Detailed analysis revealed that strain MSR2 belongs to a rare group of Pantoea strains possessing an astonishing number of plant growth promotion genes, including those involved in nitrogen fixation, phosphate solubilization, 1-aminocyclopropane-1-carboxylic acid deaminase activity, indoleacetic acid and cytokinin biosynthesis, and jasmonic acid metabolism. Moreover, the genome of this bacterium also contains genes involved in the metabolism of lignin and other plant cell wall compounds, quorum-sensing mechanisms, metabolism of plant root exudates, bacterial attachment to plant surfaces and resistance to plant defences. Importantly, the analysis revealed that most of these genes are present on accessory plasmids that are found within a small subset of Pantoea genomes, reinforcing the idea that Pantoea evolution is largely mediated by plasmids, providing new insights into the evolution of beneficial plant-associated Pantoea.