Nanoscale sulfur alters the bacterial and eukaryotic communities of the tomato rhizosphere and their interactions with a fungal pathogen

Nanoformulations of sulfur have demonstrated the potential to enhance plant growth and reduce disease incidence when plants are confronted with pathogens. However, the impact of nanoscale sulfur on microbial communities in close contact with the plant root, known as the rhizosphere, remain poorly characterized. In this study, we investigate the impact of three formulations of sulfur; bulk sulfur, uncoated (pristine) sulfur nanoparticles, and stearic acid coated sulfur nanoparticles, on the rhizosphere of tomato plants. Tomato plants were additionally challenged by the pathogenic fungus Fusarium oxysporum f. sp. Lycopersici. Employing bacterial 16S rRNA gene sequencing, along with recently in-house designed peptide nucleic acid clamps to facilitate the recovery of microeukaryote sequences, we performed a comprehensive survey of rhizosphere microbial populations. We found the largest influence on the composition of the rhizosphere microbiome was the presence of the fungal pathogen. However, sulfur amendments also drove state changes in the rhizosphere populations; for example, enriching the relative abundance of the plant-beneficial sulfur-oxidizing bacterium Thiobacillus. Notably, when investigating the response of the rhizosphere community to the different sulfur amendments, there was a strong interaction between the fungal pathogen and sulfur treatments. This resulted in different bacterial and eukaryotic taxa being enriched in association with the different forms of sulfur, which was dependent on the presence of the pathogen. These data point to nano formulations of sulfur exerting unique shifts in the rhizosphere community compared to bulk sulfur, particularly in association with a plant pathogen, and have implications for the sustainable use of nanoscale strategies in sustainable agriculture.