A highly conserved core bacterial microbiota with nitrogen-fixation capacity inhabits the xylem sap in maize plants

Abstract

Microbiomes are important for crop performance. However, a deeper knowledge of crop-associated microbial communities is needed to harness beneficial host-microbe interactions. Here, by assessing the assembly and functions of maize microbiomes across soil types, climate zones, and genotypes, we found that the stem xylem selectively recruits highly conserved microbes dominated by Gammaproteobacteria. We showed that the proportion of bacterial taxa carrying the nitrogenase gene (nifH) was larger in stem xylem than in other organs such as root and leaf endosphere. Of the 25 core bacterial taxa identified in xylem sap, several isolated strains were confirmed to be active nitrogen-fixers or to assist with biological nitrogen fixation. On this basis, we established synthetic communities (SynComs) consisting of two core diazotrophs and two helpers. GFP-tagged strains and 15N isotopic dilution method demonstrated that these SynComs do thrive and contribute, through biological nitrogen fixation, 11.8% of the total N accumulated in maize stems. These core taxa in xylem sap represent an untapped resource that can be exploited to increase crop productivity.

Synergic mitigation of saline-alkaline stress in wheat plant by silicon and Enterobacter sp. FN0603

“…It is generally realized that most endophytic microorganisms are derived from soil and optional, coming from soil and colonizing in plant tissues after selecting by plant and competing with other microbiota ( Santos and Olivares, 2021 ). Some important endophytic microbiotas would be enriched with increasing the relative abundance responded to environmental stress ( Santos and Olivares, 2021 ; Zhang et al, 2022 ). Treating seeds with FN0603 failed to markedly increase the strain’s relative abundance and distinctly change the microorganism community structure in the rhizosphere soil, but it significantly enhanced the strain’s relative abundance and changed the microorganism community structure in root endophytes.…”

Synergistic effects of diazotrophs and arbuscular mycorrhizal fungi on soil biological nitrogen fixation after three decades of fertilization

“…Biological nitrogen (N) fixation (BNF), a vital ecological process for the conversion of atmospheric N to biologically available N, occurs via symbiotic or asymbiotic (free-living) pathways and is responsible for fixing 40-100 Tg N year −1 to the terrestrial ecosystem [1]. Although symbiotic BNF contributes a major proportion of total BNF [2], asymbiotic BNF occurs nearly ubiquitously in the soil, litter layer, and even stalk and leaves of plants and is equally crucial for the terrestrial N budgets of the earth [2][3][4]; for instance, farmland soil can contribute up to 22-53 kg N ha −1 year −1 [5]. Nevertheless, large amounts of inorganic or organic N inputs challenge the contributions of BNF and the associated microorganisms, as N fixers (diazotrophs) theoretically downregulate BNF rates or are outcompeted by nondiazotrophs under N-rich conditions [6,7], owing to the fact that N uptake directly from the soil is less energetically expensive than BNF [8].…”

Genomic Characterization of Aureimonas altamirensis C2P003—A Specific Member of the Microbiome of Fraxinus excelsior Trees Tolerant to Ash Dieback

“…A special role in the microbiome is played by plant beneficial bacteria that effectively colonize the plant and contribute to nutrient supply [4,5] and/or defence against pathogens by direct antagonism, competition or plant-supporting metabolic activities [6][7][8]. The abundance of these microorganisms in the microbiome has been linked to plant growth and health in several studies [9][10][11]. The spread of pathogens may have dramatic effects on ecosystem functioning, particularly in forests.…”