PGPR-Soil Microbial Communities' Interactions and Their Influence on Wheat Growth Promotion and Resistance Induction against Mycosphaerella graminicola.

The efficiency of plant-growth-promoting rhizobacteria (PGPR) may not be consistently maintained under field conditions due to the influence of soil microbial communities. The present study aims to investigate their impact on three PGPR-based biofertilizers in wheat. We used the PGPR Paenibacillus sp. strain B2 (PB2), PB2 in co-inoculation with Arthrobacter agilis 4042 (Mix 2), or with Arthrobacter sp. SSM-004 and Microbacterium sp. SSM-001 (Mix 3). Inoculation of PB2, Mix 2, and Mix 3 into non-sterile field soil had a positive effect on root and aboveground dry biomass, depending on the wheat cultivar. The efficiency of the PGPR was further confirmed by the protection they provided against Mycosphaerella graminicola, the causal agent of Septoria leaf blotch disease. PB2 exhibited protection of ≥37.8%, while Mix 2 showed ≥47.9% protection in the four cultivars tested. These results suggest that the interactions between PGPR and native soil microbial communities are crucial for promoting wheat growth and protection. Additionally, high-throughput sequencing of microbial communities conducted 7 days after PGPR inoculations revealed no negative effects of PB2, Mix 2, and Mix 3 on the soil microbial community structure. Interestingly, the presence of Arthrobacter spp. appeared to mitigate the potential negative effect of PB2 on bacterial community and foster root colonization by other beneficial bacterial strains.

Sphingomonas sediminicola Dae20 Is a Highly Promising Beneficial Bacteria for Crop Biostimulation Due to Its Positive Effects on Plant Growth and Development.

Current agricultural practices rely heavily on synthetic fertilizers, which not only consume a lot of energy but also disrupt the ecological balance. The overuse of synthetic fertilizers has led to soil degradation. In a more sustainable approach, alternative methods based on biological interactions, such as plant growth-promoting bacteria (PGPRs), are being explored. PGPRs, which include both symbiotic and free-living bacteria, form mutualistic relationships with plants by enhancing nutrient availability, producing growth regulators, and regulating stress responses. This study investigated the potential of Sphingomonas sediminicola Dae20, an α-Proteobacteria species commonly found in the rhizosphere, as a beneficial PGPR. We observed that S. sediminicola Dae20 stimulated the root system and growth of three different plant species in the Brassicaceae family, including Arabidopsis thaliana, mustard, and rapeseed. The bacterium produced auxin, nitric oxide, siderophores and showed ACC deaminase activity. In addition to activating an auxin response in the plant, S. sediminicola Dae20 exhibited the ability to modulate other plant hormones, such as abscisic acid, jasmonic acid and salicylic acid, which are critical for plant development and defense responses. This study highlights the multifunctional properties of S. sediminicola Dae20 as a promising PGPR and underscores the importance of identifying effective and versatile beneficial bacteria to improve plant nutrition and promote sustainable agricultural practices.

Optimizing Crop Production with Bacterial Inputs: Insights into Chemical Dialogue between Sphingomonas sediminicola and Pisum sativum.

The use of biological inputs is an interesting approach to optimize crop production and reduce the use of chemical inputs. Understanding the chemical communication between bacteria and plants is critical to optimizing this approach. Recently, we have shown that Sphingomonas (S.) sediminicola can improve both nitrogen supply and yield in pea. Here, we used biochemical methods and untargeted metabolomics to investigate the chemical dialog between S. sediminicola and pea. We also evaluated the metabolic capacities of S. sediminicola by metabolic profiling. Our results showed that peas release a wide range of hexoses, organic acids, and amino acids during their development, which can generally recruit and select fast-growing organisms. In the presence of S. sediminicola, a more specific pattern of these molecules took place, gradually adapting to the metabolic capabilities of the bacterium, especially for pentoses and flavonoids. In turn, S. sediminicola is able to produce several compounds involved in cell differentiation, biofilm formation, and quorum sensing to shape its environment, as well as several molecules that stimulate pea growth and plant defense mechanisms.

Sphingomonas sediminicola Is an Endosymbiotic Bacterium Able to Induce the Formation of Root Nodules in Pea (Pisum sativum L.) and to Enhance Plant Biomass Production.

The application of bacterial bio-inputs is a very attractive alternative to the use of mineral fertilisers. In ploughed soils including a crop rotation pea, we observed an enrichment of bacterial communities with Sphingomonas (S.) sediminicola. Inoculation experiments, cytological studies, and de novo sequencing were used to investigate the beneficial role of S. sediminicola in pea. S. sediminicola is able to colonise pea plants and establish a symbiotic association that promotes plant biomass production. Sequencing of the S. sediminicola genome revealed the existence of genes involved in secretion systems, Nod factor synthesis, and nitrogenase activity. Light and electron microscopic observations allowed us to refine the different steps involved in the establishment of the symbiotic association, including the formation of infection threads, the entry of the bacteria into the root cells, and the development of differentiated bacteroids in root nodules. These results, together with phylogenetic analysis, demonstrated that S. sediminicola is a non-rhizobia that has the potential to develop a beneficial symbiotic association with a legume. Such a symbiotic association could be a promising alternative for the development of more sustainable agricultural practices, especially under reduced N fertilisation conditions.