Effects of natural non-volcanic CO2 leakage on soil microbial community composition and diversity

Biofilm development on fractured rock in oligotrophic nitrate-rich groundwater: An in-situ bioreactor study

Biofilms drive all biogeochemical processes and represent the main mode of existence for active microbial life. Many past studies examined biofilm formation under static and eutrophic conditions, but those conditions are not representative of typical groundwater environments. In this study, we developed in situ bioreactors and methodologies to examine the influence of subsurface properties such as redox condition and lithology on the properties of naturally formed biofilms in two adjacent wells, a 30-m deep well completed in alluvium and a 120-m deep well in gneiss bedrock. The bulk chemistry of groundwater from the wells was similar, with neutral pH and abundant nitrate (21.9-24.6 mg/L), but redox conditions differed with depth (alluvial: oxic, gneiss bedrock: anoxic). Microbial community analysis revealed distinct clustering of biofilm community composition with the groundwater environment. Biofilm communities were consistently assembled by deterministic processes whereas planktonic communities had a higher influence of stochastic processes. Alluvial biofilms exhibited more diverse communities mainly composed of organotrophic aerobes capable of nitrate utilization. Bedrock biofilms indicated similar community compositions with groundwater where anaerobic denitrifiers coupled with sulfur oxidizers were dominant. Visualization and biomass quantification revealed distinct morphologies and development of biofilm along rock types and groundwater environments. Biofilm on gneiss surface had more biomass and formed a thin layered structure, compared to sandstone biofilm which had a randomly distributed pattern, implying that the morphology of biofilm was governed by the properties of the rock. Attached to unattached (planktonic) microbe ratios ranged from 3.9 × 103 to 1.2 × 104: 1 in the gneiss surface and 3.4 × 102 to 4.2 × 102: 1 in the sandstone surface in bedrock groundwater environment. Taken together, this study advances our understanding of subsurface biomass abundance and demonstrates that the in-situ bioreactors are effective for cultivating and analyzing of subsurface biofilms. Based on the specific field conditions tested, we found that biofilm can form stably on fractured rock surfaces within a year, with groundwater redox conditions shaping community composition and rock types determining biofilm volume and morphology. The methodologies presented here can be extended to other subsurface environments with varying groundwater geochemistry and lithology, which will help further refine estimates of microbial life and its role in subsurface ecosystems.

Microbial Fe(III) reduction across a pH gradient: The impacts on secondary mineralization and microbial community development

Fe(III) (hydr)oxides are prevalent in natural environments where they impact contaminant mobility, greenhouse gas release, and nutrient cycling. In anoxic conditions, dissimilatory iron reducing bacteria (DIRB) and other microbial groups primarily drive Fe(III) reduction. Dissimilatory iron reduction (DIR) results in the reductive dissolution of Fe(III) phases and subsequent secondary mineralization. These processes are highly sensitive to pH changes, since protons serve as reactants in DIR. However, there is limited understanding of how DIR impacts secondary mineralization and microbial community development under relevant pH gradients. This study investigated the impact of initial pH (6.3, 6.9, 7.3, 7.7, 9) and Fe(III) source (goethite, lepidocrocite) on DIR, using acetate as the electron donor. The rate and extent of Fe(III) reduction decreased with increasing pH and that lepidocrocite, with its relatively lower crystallinity compared to goethite, supported greater DIR activity. Solid phase analyses revealed predominant formation of siderite alongside lepidocrocite reduction in microcosms with initial pH at 6.3 and 6.9. Similarly, in microcosms with initial pH at 7.3 and 7.7, partial transformation to siderite occurred. In contrast, goethite-amended microcosms did not show clear mineralogical transformations, despite the observed Fe(II) production. Microbial community analysis using 16S rRNA sequencing indicated greater enrichment of DIRB at lower pH, with a decline in abundance as pH increased. Overall, pH influenced DIR more than Fe mineralogy, highlighting its critical role in DIR processes, secondary mineral formation, and DIRB community development. This study further provides insights for developing remediation strategies involving microbial Fe(III) reduction under varying pH conditions.

Bio-based two-dimensional amphiphile with hierarchical self-assembly for enhancing pesticide utilization and reducing environmental risks

BACKGROUND

Biotic and abiotic stresses threaten crop growth and yield. Agrochemicals are an important way to mitigate biotic stress, while frequent low utilization and potential environmental risk affect their sustainable use. In order to improve pesticide utilization, it is common practice to add tank-mix adjuvants by reducing surface tension or forming spherical self-assembly. However, there is a lack of quantitative indicators to screen suitable molecules for sustainable application. In this work, critical factors based on physicochemical properties, and kinetic and thermodynamic parameters are applied to analyze regulatory mechanisms in dynamic processes, and ultimately to establish an integrated strategy for the management of stresses.

RESULTS

Compared with traditional one-dimensional linear amphiphilic molecules, two-dimensional bio-based amphiphilic molecules, especially sodium deoxycholate (NaDC), form self-assembly and could significantly promote the deposition of agrochemical droplets due to maximum energy dissipation. Meanwhile, NaDC increased the inhibition rate of pyraclostrobin against Rhizoctonia solani from 24.4% to about 100.0%, which was beneficial for pesticide resistance to biotic stress. In addition, NaDC could significantly mitigate the harmful effects of salt stress on Oryza sativa by increasing the germination rate of salt-stressed seeds by about 30%, and reducing the environmental risk of pesticides to soil microbial communities for eco-friendly crop protection.

CONCLUSION

Herein, this work demonstrates a sustainable strategy for crop management that enhances the effects of agrochemicals on biotic stresses, mitigates abiotic stresses, and significantly reduces environmental risks. © 2025 Society of Chemical Industry.

Temperature-dependent microbial reactions by indigenous microbes in bentonite under Fe(III)- and sulfate-reducing conditions

Bentonite is a promising buffer material for constructing spent nuclear fuel (SNF) repositories. However, indigenous microbes in bentonite can be introduced to the repository and subsequent sealing of the repository develops anoxic conditions over time which may stimulate fermentation and anaerobic respiration, possibly affecting bentonite structure and SNF repository stability. Moreover, the microbial activity in the bentonite can be impacted by the heat generated from radionuclides decay. Therefore, to investigate the temperature effect on microbial activities in bentonite, we created microcosms with WRK bentonil (a commercial bentonite) using lactate as the electron donor, and sulfate and/or ferrihydrite (Fe(III)) as electron acceptors with incubation at 18 ℃ and 50 ℃. Indigenous WRK microbes reduced sulfate and Fe(III) at both temperatures but with different rates and extents. Lactate was metabolized to acetate at both temperatures, but only to propionate at 18 ℃ during early-stage microbial fermentation. More Fe(III)-reduction at 18 ℃ but more sulfate-reduction at 50 ℃ was observed. Thermophilic and/or metabolically flexible microbes were involved in both fermentation and Fe(III)/sulfate reduction. Our findings illustrate the necessity of considering the influence of temperature on microbial activities when employing bentonite as an engineered buffer material in construction of SNF repository barriers.

Effects of livestock grazing on the relationships between soil microbial community and soil carbon in grassland ecosystems

Livestock grazing of grassland ecosystems may induce shifts in microbe community traits and soil carbon (C) cycling; however, impacts of grassland management (grazing) on soil C- microbe community trait (microbial biomass, diversity, community structure, and enzyme activity) relationships are unclear. To address this, we conducted a global meta-analysis of 95 articles of livestock grazing studies that vary in grazing intensities (light, moderate, and high) and durations (<5 years, 5-10 years, and > 10 years). We found that gazing decreased soil organic carbon content (SOC; 10.1 %), and activities of the enzymes of saccharase (SA; 31.1 %), urease (UA; 7.0 %), and acid phosphatase (11.9 %) in topsoil. Meanwhile, the SOC, soil microbial biomass and enzyme activities consistently decreased as grazing intensity and duration prolonged. Furthermore, we observed strong linear relationships of microbe community traits with SOC (p < 0.05), but weak relationships with soil N or P (p > 0.05) in grasslands, which also depends on the grazing intensity and duration. In conclusion, our results indicate that traits of soil carbon content, soil microbe community, and in particular their relationships in global grasslands are overall significantly affected by livestock grazing, but the effects strongly depend on the grazing intensity and duration.