Assist.-Prof. Dr. Barbara Bayer






Assistant Professor at the Division of Microbial Ecology

☎ +43 1 4277 91251

Oceans and lakes are home to a plethora of different microorganisms which drive biogeochemical cycles on our planet. Barbara Bayer’s research focusses on the interactions between aquatic microorganisms and their environment and on understanding the environmental regulation of microbial processes that control carbon and nitrogen cycling in the water column.

Barbara and her team combine diverse isotope approaches, cultivation, and multi-omics techniques to quantify biogeochemical processes and identify novel microorganisms and metabolic pathways. Barbara has received an ERC Starting Grant to investigate microbial methane cycling in aquatic ecosystems and has also been granted an Austrian Science Fund (FWF) START Award.

Research Topics

The influence of nitrifiers on the oceanic carbon cycle

Understanding how carbon is cycled on the way to the ocean floor has important implications for the way we model the carbon cycle, and predict the ocean's role in mitigating climate change. In addition to microorganisms that consume organic carbon, the deep ocean is also home to an abundant community of microorganisms that can use chemical energy to convert inorganic carbon into biomass (chemoautotrophy). These organisms are able to oxidize, for example, reduced nitrogen compounds such as ammonia and nitrite to generate the energy they need for the fixation of inorganic carbon. This newly fixed carbon represents an important nutritional foundation for heterotrophic food webs in the deep ocean.


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To view Barbara Bayer's teaching activities at the University of Vienna, visit u:find.

Nitrifying microorganisms, including ammonia-oxidizing archaea (AOA), ammonia-oxidizing bacteria (AOB), and nitrite-oxidizing bacteria (NOB), are the most abundant chemoautotrophs in the ocean. The results of this study elucidate the diverse roles of nitrifying microorganisms in the oceanic carbon cycle, including the release of dissolved organic carbon into the environment (Bayer et al. 2019Bayer et al. 2023) and the use of alternative energy sources (Bayer et al. 2021). Furthermore, our findings provide values for biogeochemical models of the global carbon cycle, and help to further constrain the relationship between carbon and nitrogen fluxes in the nitrification process (Zakem et al. 2022).​

Microbial methane cycling in aquatic ecosystems

Aquatic ecosystems are a major source of the potent greenhouse gas methane, accounting for half of the global methane emissions. Biogenic methane is microbially produced in anoxic sediments and typically rapidly consumed by methanotrophic microorganisms, largely limiting emissions to the atmosphere (“microbial methane filter”). However, methane concentrations are often elevated in oxic surface waters of oceans and lakes (“methane paradox”). Due its proximity to the atmosphere, aerobic methane production in surface waters might constitute a particularly important source of methane, which might escape the aquatic “microbial methane filter”. Yet, we currently lack a comprehensive understanding of the involved processes and microorganisms. Moreover, enhanced eutrophication of coastal ocean and lake ecosystems due to human activities has been linked to increased methane emissions. However, we know remarkably little about how changes in environmental conditions affect the in situ activities of diverse methane-cycling microorganisms, which is of central importance to better predict future climate developments.

We will address these knowledge gaps by i) resolving and quantifying aerobic methane production in surface waters of aquatic ecosystems with different trophic states, and ii) unravelling how eutrophication affects methane-consuming microorganisms in water columns of coastal ocean and lake ecosystems.

  • European Research Council (ERC) Starting Grant METHANIAQ (2024-2029), PI: Barbara Bayer

Group Members


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