Ultra-small bacteria and archaea exhibit genetic flexibility towards groundwater oxygen content, and adaptations for attached or planktonic lifestyles

Aquifers are populated by highly diverse microbial communities, including unusually small bacteria and archaea. The recently described Patescibacteria (or Candidate Phyla Radiation) and DPANN radiation are characterized by ultra-small cell and genomes sizes, resulting in limited metabolic capacities and probable dependency on other organisms to survive. We applied a multi-omics approach to characterize the ultra-small microbial communities over a wide range of aquifer groundwater chemistries. Results expand the known global range of these unusual organisms, demonstrate the wide geographical range of over 11,000 subsurfaceadapted Patescibacteria, Dependentiae and DPANN archaea, and indicate that prokaryotes with ultra-small genomes and minimalistic metabolism are a characteristic feature of the terrestrial subsurface. Community composition and metabolic activities were largely shaped by water oxygen content, while highly site-specific relative abundance profiles were driven by a combination of groundwater physicochemistries (pH, nitrate-N, dissolved organic carbon). We provide insights into the activity of ultra-small prokaryotes with evidence that they are major contributors to groundwater community transcriptional activity. Ultra-small prokaryotes exhibited genetic flexibility with respect to groundwater oxygen content, and transcriptionally distinct responses, including proportionally greater transcription invested into amino acid and lipid metabolism and signal transduction in oxic groundwater, along with differences in taxa transcriptionally active. Those associated with sediments differed from planktonic counterparts in species composition and transcriptional activity, and exhibited metabolic adaptations reflecting a surfaceassociated lifestyle. Finally, results showed that groups of phylogenetically diverse ultra-small organisms co-occurred strongly across sites, indicating shared preferences for groundwater conditions.publishedVersio

Understanding hydrochemical processes using 3D models and hydrochemical facies in Wairau Plain groundwater, Marlborough

Three dimensional models and groundwater quality are combined to better understand and conceptualise groundwater systems in complex geological settings in the Wairau Plain, Marlborough. Hydrochemical facies, which are characteristic of distinct evolutionary pathways and a common hydrologic history of groundwaters, are identified within geological formations to assess natural water-rock interactions, redox potential and human agricultural impact on groundwater quality in the Wairau Plain

Bacterial surfaces inhibit the oxidation of Fe(II)

International audienceBacteria are known to affect the fate of metals through sorption reactions. Secondary minerals, such as iron-oxides, are another important phase scavenging metals in the environment. It has often been suggested that bacterial surfaces favor the precipitation of iron-oxide phases. In this study, we demonstrate that this is not the case. We have mimicked the processes occurring at an oxic interface, which lead to the formation of iron oxides, by introducing progressively a fixed total amount of Fe2+ ions at a fixed pH of 6.5 in an aerobic reactor in the absence and in the presence of increasing concentrations of Bacillus subtilis bacterial cells. Alternatively, increasing amounts of Fe2+ ions were added to a fixed concentration of Anoxybacillus flavithermus bacterial cells. The kinetics of the reaction were monitored by measuring the rate of addition of the base needed to maintain the pH constant. In another set of experiments, we added Fe2+ ions at once in anaerobic conditions and oxygenated the suspension afterwards. The rate of oxidation of the Fe(II) was then measured directly using the ferrozine colorimetric method. In both types of experiments, it was clearly observed that the kinetics of oxidation of the Fe(II) are dramatically reduced by the presence of the bacterial cells. This is an important result, as the oxidation state and the speciation of the sorbed Fe impact the immobilization by the bacterial-iron composite suspensions of other metals. For instance, we have observed that a given amount of Fe reduces the Cd sorption ability of the cells, and it does this more effectively when it occurs as a sorbed Fe(II) species as when it is precipitated as adhering iron oxide nanoparticles

Three-dimensional geological modeling and multivariate statistical analysis of water chemistry data to analyse and visualise aquifer structure and groundwater composition in the Wairau Plain, Marlborough District, New Zealand

Concerns regarding groundwater contamination with nitrate and the long-term sustainability of groundwater resources have prompted the development of a multi-layered three dimensional (3D) geological model to characterise the aquifer geometry of the Wairau Plain, Marlborough District, New Zealand. The 3D geological model which consists of eight litho-stratigraphic units has been subsequently used to synthesise hydrogeological and hydrogeochemical data for different aquifers in an approach that aims to demonstrate how integration of water chemistry data within the physical framework of a 3D geological model can help to better understand and conceptualise groundwater systems in complex geological settings. Multivariate statistical techniques(e.g. Principal Component Analysis and Hierarchical Cluster Analysis) were applied to groundwater chemistry data to identify hydrochemical facies which are characteristic of distinct evolutionary pathways and a common hydrologic history of groundwaters. Principal Component Analysis on hydrochemical data demonstrated that natural water-rock interactions, redox potential and human agricultural impact are the key controls of groundwater quality in the Wairau Plain. Hierarchical Cluster Analysis revealed distinct hydrochemical water quality groups in the Wairau Plain groundwater system. Visualisation of the results of the multivariate statistical analyses and distribution of groundwater nitrate concentrations in the context of aquifer lithology highlighted the link between groundwater chemistry and the lithology of host aquifers. The methodology followed in this study can be applied in a variety of hydrogeological settings to synthesise geological, hydrogeological and hydrochemical data and present them in a format readily understood by a wide range of stakeholders. This enables a more efficient communication of the results of scientific studies to the wider community