Microbial strategy under saline alkali challenge: Sphingomonas sp. HG43 promotes Arabidopsis growth and enhances salt resistance

Soil salinization, as a major global challenge, has had adverse effects on agriculture and ecosystems. Plant growth promoting bacteria (PGPB) can enhance plant tolerance to biotic and abiotic stresses and are important microbial resources. However, the dynamic response strategies of rhizosphere microbiota at different developmental stages of plants to PGPB under salt stress are still unclear, and the relationship between PGPB, microbiota, and plants is largely unknown. Therefore, this study monitored the colonization dynamics of HG43 and explored the effects of the growth promoting bacterium Sphingomonas sp. HG43 on the growth and physiological processes of Arabidopsis under salt stress, as well as the succession patterns of bacterial communities at different stages of plant development. Research has found that HG43 can colonize the rhizosphere soil, roots, and leaves of Arabidopsis thaliana for a long time. It significantly increases the activities of SOD, POD, and CAT in Arabidopsis thaliana, reduces MDA content, promotes the accumulation of osmotic regulator proline, thereby improving plant salt tolerance and increasing its biomass. Linear mixed model analysis shows that the assembly of rhizosphere bacterial communities is influenced by the interaction of Arabidopsis developmental stage, HG43, and salt stress, and the community composition exhibits three patterns of change with developmental stage: basically unchanged, increasing, and decreasing. The null model analysis results showed that HG43 had a significant impact on the assembly of rhizosphere bacterial communities at all three stages of plant development, especially during the bolting stage. In addition, FAPROTAX functional prediction found that HG43 enhances the potential ecological functions of plant rhizosphere soil and leaf rhizosphere by enriching and recruiting beneficial bacteria, such as nitrogen fixation, nitrate respiration, and urea decomposition, thereby promoting plant growth under salt stress. In summary, HG43 is a valuable bacterial strain that can colonize soil and plants for a long time. It enhances physiological processes such as plant reactive oxygen species clearance, changes bacterial community structure, recruits beneficial bacteria, and synergistically promotes plant growth and resistance to salt stress. These results further deepen our understanding of the microbiological mechanisms by which PGPB helps Arabidopsis resist salt stress, and also enrich the strain resources for future application in agricultural biofertilizers.