Genome-Wide Association Studies across Environmental and Genetic Contexts Reveal Complex Genetic Architecture of Symbiotic Extended Phenotypes

Co-inoculation with novel nodule-inhabiting bacteria reduces the benefits of legume-rhizobium symbiosis

The ecologically and economically vital symbiosis between nitrogen-fixing rhizobia and leguminous plants is often thought of as a bi-partite interaction, yet studies increasingly show the prevalence of non-rhizobial endophytes (NREs) that occupy nodules alongside rhizobia. Yet, what impact these NREs have on plant or rhizobium fitness remains unclear. Here, we investigated four NRE strains found to naturally co-occupy nodules of the legume Medicago truncatula alongside Sinorhizobium meliloti in native soils. Our objectives were to (1) examine the direct and indirect effects of NREs on M. truncatula and S. meliloti fitness, and (2) determine whether NREs can re-colonize root and nodule tissues upon reinoculation. We identified one NRE strain (522) as a novel Paenibacillus species, another strain (717A) as a novel Bacillus species, and the other two (702A and 733B) as novel Pseudomonas species. Additionally, we found that two NREs (Bacillus 717A and Pseudomonas 733B) reduced the fitness benefits obtained from symbiosis for both partners, while the other two (522, 702A) had little effect. Lastly, we found that NREs were able to co-infect host tissues alongside S. meliloti. This study demonstrates that variation of NREs present in natural populations must be considered to better understand legume-rhizobium dynamics in soil communities.

Engineering agricultural soil microbiomes and predicting plant phenotypes

Plant growth-promoting rhizobacteria (PGPR) can improve crop yields, nutrient use efficiency, plant tolerance to stressors, and confer benefits to future generations of crops grown in the same soil. Unlocking the potential of microbial communities in the rhizosphere and endosphere is therefore of great interest for sustainable agriculture advancements. Before plant microbiomes can be engineered to confer desirable phenotypic effects on their plant hosts, a deeper understanding of the interacting factors influencing rhizosphere community structure and function is needed. Dealing with this complexity is becoming more feasible using computational approaches. In this review, we discuss recent advances at the intersection of experimental and computational strategies for the investigation of plant-microbiome interactions and the engineering of desirable soil microbiomes.

The evolutionary ecology of rhizobia: multiple facets of competition before, during, and after symbiosis with legumes

Rhizobial bacteria have complex lifestyles that involve growth and survival in bulk soil, plant rhizospheres and rhizoplanes, legume infection threads, and mature and senescing legume nodules. In nature, rhizobia coexist and compete with many other rhizobial strains and species to form host associations. We review recent work defining competitive interactions across these environments. We highlight the use of sophisticated measurement tools and sequencing technologies to examine competition mechanisms in planta, and highlight environments (e.g. soil and senescing nodules) where we still know exceedingly little. We argue that moving toward an explicitly ecological framework (types of competition, resources, and genetic differentiation) will clarify the evolutionary ecology of these foundational organisms and open doors for engineering sustainable, beneficial associations with hosts.

Influencing Factors and Symbiotic Mechanism of the Integration of Medical Care and Disease Prevention during the COVID-19 Pandemic: A Cross-Sectional Survey of Public Hospital Employees

Background: The COVID-19 outbreak has accelerated the huge difference between medical care and disease prevention in Chinese medical institutions. This study aimed to investigate the relationship between the symbiotic units, environments, models, and effects of the integration of medical care and disease prevention. Methods: This cross-sectional study involved 762 employees of public hospitals in 11 cities in Zhejiang Province by random stratified sampling. We analyzed the influence paths of elements in the mechanism of integration of medical care and disease prevention and the mediating effect of symbiotic models among symbiotic units, symbiotic environments, and effects on this integration. Results: The path coefficient of the symbiotic unit on the symbiosis model was 0.46 (p < 0.001), the path coefficient of the symbiotic environment on the symbiosis model was 0.52 (p < 0.001). The path coefficient of the symbiotic unit and the environment was 0.91 (p < 0.001). The symbiotic models exhibited a partial mediation effect between symbiotic units and the effect of this integration. Sobel test = 3.27, β = 0.152, and the mediating effect accounted for 34.6%. Conclusions: It is suggested that health policymakers and public hospital managers should provide sufficient symbiotic units, establish collaborative symbiotic models, and improve the effects of integration of medical care and disease prevention in public hospitals.