Biology subjects

Kallmeyer, J.

Publications and source records attributed to Kallmeyer, J..

3 recordsLinked to original sources

bioRxiv2024

Subsurface Microbial Colonization at Mineral-Filled Veins in 2-Billion-Year-Old Igneous Rock from the Bushveld Complex, South Africa

Recent advances in subsurface microbiology have demonstrated the habitability of multi-million-year-old igneous rocks, despite the scarce energy supply from rockwater interactions. Given the minimal evolution coupled with exceedingly slow metabolic rates in subsurface ecosystems, spatiotemporally stable igneous rocks can sustain microbes over geological time scales. This study investigated 2-billion-year-old igneous rock in the Bushveld Complex, South Africa, where ultradeep drilling is being executed by the International Continental Scientific Drilling Program (ICDP). New procedures were successfully developed to simultaneously detect indigenous and contaminant microbial cells in a drill core sample. Precision rock sectioning coupled with infrared, fluorescence and electron microscopy imaging of the rock section with submicron resolution revealed microbial colonization in veins filled with smectite. The entry and exit of microbial cells in the veins are severely limited by tight packing with smectite, the formation of which supplies energy sources for long-term habitability. Further microbiological characterization of drilled rock cores from the Bushveld Complex will expand the understanding of microbial evolution in deep igneous rocks over 2 billion years.

microbiology↗

bioRxiv2022

Microbial diversity and community dynamics in an active, high CO2 subsurface rift ecosystem

The Eger Rift subsurface is characterized by frequent seismic activity and consistently high CO2 concentrations, making it a unique deep biosphere ecosystem and a suitable site to study the interactions between volcanism, tectonics, and microbiological activity. Pulses of geogenic H2 during earthquakes may provide substrates for methanogenic and chemolithotrophic processes, but very little is currently known about the role of subsurface microorganisms and their cellular processes in this type of environment. To assess the impact of geologic activity on microbial life, we analyzed the geological, geochemical, and microbiological composition of rock and sediment samples from a 240 m deep drill core, running across six lithostratigraphic zones. In addition, we evaluated diversity as well as metabolic attributes of bacterial and archaeal communities. Our investigation revealed a distinct low biomass community, with a surprisingly diverse Archaea population, providing strong support that methanogenic archaea reside in the Eger subsurface. Geochemical analysis revealed sulfate and sodium concentrations as high as 1000 mg L-1 in sediment samples from a depth between 50 and 100 m and in weathered rock samples collected below 200 m. Most microbial signatures could be assigned to common soil and water bacteria, which together with the occurrence of freshwater Cyanobacteria at specific depths, emphasize the heterogenous, groundwater movement driven nature of this terrestrial subsurface environment. Although not as frequently and abundantly as initially expected, our investigations also found evidence for anaerobic, autotrophic, and acidophilic communities in Eger Rift sediments, as sulfur cycling taxa like Thiohalophilus and Desulfosporosinus were specifically enriched at depths below 100 m. The detection of methanogenic, halophilic, and ammonia oxidizing archaeal populations demonstrate that the unique features of the Eger Rift subsurface environment provide the foundation for diverse types of microbial life, including the microbial utilization of geologically derived CO2 and when available H2, as a primary energy source.

microbiology↗

bioRxiv2022

Anaerobic methane oxidizing archaea offset sediment methane concentrations in Arctic thermokarst lagoons

Thermokarst lagoons represent the transition state from a freshwater lacustrine to a marine environment, and receive little attention regarding their role for greenhouse gas production and release in Arctic permafrost landscapes. We studied the fate of methane (CH4) in sediments of a thermokarst lagoon in comparison to two thermokarst lakes on the Bykovsky Peninsula in northeastern Siberia through the analysis of sediment CH4 concentrations and isotopic signature, methane-cycling microbial taxa, sediment geochemistry, and lipid biomarkers. We specifically assessed whether sulfate-driven anaerobic methane oxidation (S-AOM) through anaerobic methanotrophic archaea (ANMEs), common in marine sediments with constant supply of sulfate and methane, establish after thermokarst lagoon development and whether sulfate-driven ANMEs consequently oxidize CH4 that would be emitted to the water column under thermokarst lake conditions. The marine-influenced lagoon environment had fundamentally different methane-cycling microbial communities and metabolic pathways compared to the freshwater lakes, suggesting a substantial reshaping of microbial and carbon dynamics during lagoon formation. Anaerobic sulfate-reducing ANME-2a/2b methanotrophs dominated the sulfate-rich sediments of the lagoon despite its known seasonal alternation between brackish and freshwater inflow. CH4 concentrations in the freshwater-influenced sediments averaged 1.34{+/-}0.98 {micro}mol g-1, with highly depleted {delta}13C-CH4 values ranging from -89{per thousand} to -70{per thousand}. In contrast, the sulfate-affected upper 300 cm of the lagoon exhibited low average CH4 concentrations of 0.011{+/-}0.005 {micro}mol g-1 with comparatively enriched {delta}13C-CH4 values of -54{per thousand} to -37{per thousand} pointing to substantial methane oxidation. Non-competitive methylotrophic methanogens dominated the methanogenic community of the lakes and the lagoon, independent of porewater chemistry and depth. This potentially contributed to the high CH4 concentrations observed in all sulfate-poor sediments. Our study shows that S-AOM in lagoon sediments can effectively reduce sediment CH4 concentrations and we conclude that thermokarst lake to lagoon transitions have the potential to mitigate terrestrial methane fluxes before thermokarst lakes fully transition to a marine environment.

microbiology↗