Summary Subsurface groundwater‐surface water mixing zones (hyporheic zones) have enhanced biogeochemical activity, but assembly processes governing subsurface microbiomes remain a critical uncertainty in understanding hyporheic biogeochemistry. To address this obstacle, we investigated (a) biogeographical patterns in attached and waterborne microbiomes across three hydrologically‐connected, physicochemically‐distinct zones (in...

Summary Biofilms are core to a range of biological processes, including the bioremediation of environmental contaminants. Within a biofilm population, cells with diverse genotypes and phenotypes coexist, suggesting that distinct metabolic pathways may be expressed based on the local environmental conditions in a biofilm. However, metabolic responses to local environmental conditions in a metabolically active biofilm interactin...

Summary Microbial diversity in subsurface sediments at the Hanford Site 300 Area near Richland, Washington state (USA) was investigated by analysing 21 samples recovered from depths of 9–52 m. Approximately 8000 near full‐length 16S rRNA gene sequences were analysed across geological strata that include a natural redox transition zone. These strata included the oxic coarse‐grained Hanford formation, fine‐grained oxic and anoxi...

Summary The composition of extracellular polymeric substances (EPS) from Shewanella sp. HRCR‐1 biofilms was investigated using infrared spectroscopy and proteomics to provide insight into potential ecophysiological functions and redox activity of the EPS. Both bound and loosely associated EPS were extracted from Shewanella sp. HRCR‐1 biofilms prepared using a hollow‐fibre membrane biofilm reactor. Fourier transform infrared sp...

Summary We characterized the diversity of sulphate‐reducing bacteria (SRB) associated with South African gold mine boreholes and deep aquifer systems in Washington State, USA. Sterile cartridges filled with crushed country rock were installed on two hydrologically isolated and chemically distinct sites at depths of 3.2 and 2.7 km below the land surface (kmbls) to allow development of biofilms. Enrichments of sulphate‐reducing...

Summary Subsurface microbial community structure in relation to geochemical gradients and lithology was investigated using a combination of molecular phylogenetic and geochemical analyses. Discreet groundwater and substratum samples were obtained from depths ranging from 182 to 190 m beneath the surface at approximately 10‐cm intervals using a multilevel sampler (MLS) that straddled Cretaceous shale and sandstone formations at...