A Nitrate-Transforming Bacterial Community Dominates in the Miscanthus Rhizosphere on Nitrogen-Deficient Volcanic Deposits of Miyake-jima

Plant Growth-Promoting Effect and Complete Genomic Sequence Analysis of the Beneficial Rhizosphere Streptomyces sp. GD-4 Isolated from Leymus secalinus

Plant growth-promoting rhizobacteria (PGPR) are beneficial bacteria residing in the rhizosphere and are capable of enhancing plant growth through various mechanisms. Streptomyces sp. GD-4 is a plant growth-promoting bacterium isolated from the rhizosphere soil of Leymus secalinus. To further elucidate the molecular mechanisms underlying the beneficial effects of the strain on plant growth, we evaluated the growth-promoting effects of Streptomyces sp. GD-4 on forage grasses and conducted comprehensive genome mining and comparative genomic analysis of the strain. Strain GD-4 effectively colonized the rhizosphere of three forages and significantly promoted the growth of both plant roots and leaves. Genome sequence functional annotation of GD-4 revealed lots of genes associated with nitrogen, phosphorus, and sulfur metabolism. Additionally, genes potentially involved in plant growth promotion such as indole-3-acetic acid (IAA) biosynthesis, trehalose production, siderophore production, and phosphate solubilization were annotated. Whole-genome analysis revealed that GD-4 may possess molecular mechanisms involved in soil nutrient cycling in rhizosphere soil and plant growth promotion. The bacteria also possess genes associated with adaptability to abiotic stress conditions, further supporting the ability of Streptomyces sp. GD-4 to colonize nutrient-poor soils. These findings provide a foundation for further research into soil remediation technologies in plateau regions.

The structure and diversity of bacteria and fungi in the roots and rhizosphere soil of three different species of Geodorum

Shepherd's crook (Geodorum) is a genus of protected orchids that are valuable both medicinally and ornamentally. Geodorum eulophioides (GE) is an endangered and narrowly distributed species, and Geodorum densiflorum (GD) and Geodorum attenuatum (GA) are widespread species. The growth of orchids depend on microorganisms. However, there are few studies on the microbial structure in Geodorum, and little is known about the roles of microorganisms in the endangered mechanism of G. eulophioides. This study analyzed the structure and composition of bacterial and fungal communities in the roots and rhizosphere soil of GE, GD, and GA. The results showed that Delftia, Bordetella and norank_f_Xanthobacteraceae were the dominant bacteria in the roots of Geodorum, while norank_f_Xanthobacteraceae, Gaiella and norank_f_norank_o_Gaiellales were the dominant bacteria in the rhizosphere soil of Geodorum. In the roots, the proportion of Mycobacterium in GD_roadside was higher than that in GD_understory, on the contrary, the proportion of Fusarium, Delftia and Bordetella in GD_roadside was lower than that in GD_understory. Compared with the GD_understory, the roots of GD_roadside had lower microbial diversity. In the endangered species GE, Russula was the primary fungus in the roots and rhizosphere soil, with fungal diversity lower than in the more widespread species. Among the widespread species, the dominant fungal genera in the roots and rhizosphere soil were Neocosmospora, Fusarium and Coprinopsis. This study enhances our understanding of microbial composition and diversity, providing fundamental information for future research on microbial contributions to plant growth and ecosystem function in Geodorum.