Abstract Phosphorus (P) is an essential nutrient that constrains productivity across many terrestrial ecosystems. Soil microorganisms regulate P transformation through distinct functional strategies, yet how these strategies vary with land use and environmental conditions across chronically P-impoverished landscapes remains poorly understood. Here, we combined 268 soil metagenomes from natural, pasture, and cropland systems across Australia with genome-resolved analyses of 1,077 metagenome-assembled genomes (MAGs). Results revealed contrasting genomic distributions among P-cycling strategies. P accumulation genes were widely distributed across bacterial phylogeny, whereas mineralization gene and solubilisation gene were concentrated within specific lineages. Land-use-associated differences were most evident in the relative abundances of mineralisation and solubilisation genes, whereas accumulation genes showed comparatively little variation. Soil properties were stronger predictors of relative P-cycling gene abundance than climatic variables. Among these variables, soil pH was the strongest predictor of both the combined relative abundance of P-cycling genes and mineralisation genes, whereas accumulation genes were negatively associated with the mineral-associated organic carbon fraction. Continental predictions further suggested higher combined relative P-cycling gene abundance in wetter south-western and coastal eastern regions. These analyses reveal contrasting microbial P-cycling gene strategies across Australian soils and provide a genome-resolved framework for understanding their phylogenetic distributions and environmental associations at the continental scale.
Abstract Nanocarrier-based pesticide delivery platforms substantially boost agrochemical utilization efficiency, yet their cascading ecological repercussions for rhizosphere and soil microbial ecology remain insufficiently understood. Here, a star polycation (SPc) nanocarrier was employed to construct a matrine nano-formulation (MT@SPc) with typical nano-pesticide characteristics. MT@SPc and commercial matrine formulation (MT SL) were employed as representative systems to further evaluate their impacts on rhizosphere and soil microbial ecosystems. Compared with MT SL, MT@SPc reshaped rhizosphere microbial communities by suppressing phytopathogens and promoting the enrichment of beneficial bacteria. Further validation using four representative bacterial isolates obtained from soil demonstrated that MT@SPc significantly inhibited the growth of the phytopathogen Pectobacterium carotovorum, whereas enriched beneficial bacteria exhibited lower susceptibility to MT@SPc. Multi-scale mechanistic analyses revealed that MT@SPc could interact with bacterial cell surfaces through physicochemical interactions, resulting in pronounced surface deformation and structural damage in P. carotovorum. Multi-omics analyses associated with physiological and biochemical assays further demonstrated that MT@SPc disrupted cell wall and membrane integrity, leading to ionic imbalance, metabolite leakage and oxidative stress. However, beneficial bacteria maintained higher stability, and their enrichment was associated with microbial community shifts following pathogen suppression. Overall, this study reveals that nano-pesticides drive rhizosphere community restructuring through differential microbial responses, providing mechanistic insights into nano-pesticide–microbiome interactions in complex ecological systems.
Abstract The majority of marine nitrite-oxidising bacteria (NOB) belong to three uncultured genera within the Nitrospinaceae family and thus the ecophysiology of these main nitrate producing microorganisms in the ocean remains poorly resolved. Here, we report on the environmental characterization of one of these genera, which we name Candidatus Nitromaricola. A single species within this genus, Candidatus Nitromaricola pontica, comprises >95% of the nitrite-oxidising community in the permanently stratified Black Sea. This provided a unique opportunity to study this globally abundant genus in situ, across pronounced environmental gradients of oxygen and inorganic nitrogen concentrations. We show that Ca. Nitromaricola pontica is capable of oxidising nitrite at similar rates in both oxic and apparently anoxic waters, although it had a higher abundance in the more oxygenated waters of the Black Sea. The genome of Ca. Nitromaricola pontica indicates that like other NOB, it is a chemolithoautotroph, oxidising nitrite, and fixing inorganic carbon. However, Ca. Nitromaricola pontica and other members of the Ca. Nitromaricola genus lack canonical high affinity terminal oxidases found in some other NOB genera. Single-cell analyses confirmed active autotrophic growth and showed that ammonium and urea, rather than nitrite, were the main nitrogen sources for biomass production. Our findings identify Ca. Nitromaricola as a globally abundant marine NOB and highlight its cosmopolitan lifestyle.
Abstract Though they jointly shape community responses to environmental perturbations, ecology and evolution are often examined separately, even in microorganisms where both occur over short timescales. Here, we examine ecological and evolutionary responses to 33 years of nitrogen fertilization using the legume–rhizobium mutualism. Pairing a manipulative inoculation study with full-length 16S rRNA gene amplicon sequencing and structural equation modeling allows us to synthesize across biological scales: whole bacterial community, genus Rhizobium, Rhizobium amplicon sequence variants (ASVs), and symbiosis plasmids. Clover’s preferred partner decreases in N-addition soils, limiting host growth, while a diverse and largely uncharacterized Rhizobium community increases. This ecological change is compounded by a concurrent evolutionary degradation of symbiont partner quality via changing frequencies of symbiotic plasmids. Ecological (rarer symbionts) and evolutionary (inferior symbionts) processes each accounted for roughly half of this loss of host benefit, revealing that ecology and evolution jointly shape mutualism breakdown over the short timescales typical of microbial systems.
Abstract Methane emissions from rice paddies are a major source of greenhouse gases, and silicate fertilizer (SF) derived from blast furnace slag has emerged as an environmentally friendly amendment that reduces methane release. SF modifies the soil redox environment by supplying electron acceptors such as iron, but the microbial mechanisms underlying methane mitigation remain unclear. Here, we combined metagenomic profiling, microbial isolation, and greenhouse experiments to show that SF consistently enriched Burkholderia vietnamiensis together with the methanotrophs in the rice rhizosphere. Inoculation of B. vietnamiensis strain HU01 alone reproduced the methane-suppressing effect of SF and increased methanotroph abundance. Cell-free culture supernatants of HU01 stimulated the growth of Methylococcus geothermalis and Methylocystis parvus through secreted, low-molecular-weight, heat-stable metabolites. Although metabolic modeling predicted primary metabolites such as L-glutamate and cobalamin as candidate cross-feeding factors, LC–MS/MS analysis of the highly active fractions indicated that the robust bioactivity was primarily driven by a chemically complex metabolite mixture rather than these ubiquitous single compounds. These results provide direct evidence that enrichment of a single heterotrophic species can enhance methane oxidation by stimulating methanotroph activity through metabolite exchange. B. vietnamiensis HU01 represents a promising microbial resource for methane mitigation and illustrates how targeted heterotroph–methanotroph interactions can be leveraged for climate-smart rice cultivation.
