Abstract
Endophytic nitrogen-fixing (diazotrophic) bacteria are essential members of the microbiome of switchgrass (Panicum virgatum), considered to be an important commodity crop in bioenergy production. While endophytic diazotrophs are known to provide fixed atmospheric nitrogen to their host plant, there are many other plant growth-promoting (PGP) capabilities of these organisms to be demonstrated. The diversity of PGP traits across different taxa of switchgrass-colonizing endophytes is understudied, yet critical for understanding endophytic function and improving cultivation methods of important commodity crops. Here, we present the isolation and characterization of three diazotrophic endophytes: Azospirillum agricola R1C, Klebsiella variicola F10Cl, and Raoultella terrigena R1Gly. Strains R1C and F10Cl were isolated from switchgrass and strain R1Gly, while isolated from tobacco, is demonstrated herein to colonize switchgrass. Each strain exhibited highly diverse genomic and phenotypic PGP capabilities. Strain F10Cl and R1Gly demonstrated the highest functional similarity, suggesting that, while endophyte community structure may vary widely based on host species, differences in functional diversity are not a clearly delineated. The results of this study advance our understanding of diazotrophic endophyte diversity, which will allow us to design robust strategies to improve cultivation methods of many economically important commodity crops.
Highlights
Nitrogen (N) is an essential component of biomolecules such as proteins and nucleic acids, and is a key element for life and cell development
While the taxonomic diversity of switchgrass endophytes has been studied (Kim et al, 2012; Xia et al, 2013; Bahulikar et al, 2014; Wang et al, 2015; Singer et al, 2019), the functional diversity of plant growth-promoting (PGP) traits among diverse species of switchgrass-colonizing endophytes is unclear. To address this knowledge gap, we present the isolation of diazotrophic endophytes able to colonize switchgrass plant tissues and phenotypic characterization and thorough genomic comparison of three novel switchgrass-colonizing endophytes in the genera Raoultella, Azospirillum, and Klebsiella
Three hundred (300) isolates were obtained from surface sterilized and macerated roots and leaves of switchgrass and tobacco plants and evaluated for N2-fixing capacity
Summary
Nitrogen (N) is an essential component of biomolecules such as proteins and nucleic acids, and is a key element for life and cell development. Availability of N, along with phosphorus, is often the limiting factor for plants, thereby significantly reducing plant growth and biomass yield (Muir et al, 2001; Zhao et al, 2005). N is available to plants either as N fixed from the atmosphere by N2-fixing, plant-associated microorganisms or from synthetic inputs such as mineral fertilizer. To alleviate N limitation in agricultural practice, copious amounts of mineral N fertilizer are often added to maximize plant yields. While this practice has been partly responsible for the “green revolution,” it has come at high environmental and economic costs. The fertilizer industry utilizes 1.2% of the world’s energy resources and more than 90% of this is used for mineral N fertilizer production
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