Organic polymer degrading marine benthic microorganisms

Guaymas Basin in the Gulf of Mexico is a peculiar and magical place. It is permanently dark in the deep sea and the water is always cold. Yet, Guaymas Basin teems with life and is home to a diverse and biomass-rich community. The key to a functioning ecosystems in this hostile place lies in the ability of microorganisms to use subsurface derived energy – mostly methane and short-chain hydrocarbons – to fix inorganic carbon and make biomass. These chemolithoautotrophs are the base of the food web and all other organisms – such as heterotrophs like us that depend on organic carbon – live directly or indirectly of their metabolic activity. While the chemolithoautotrophic microorganisms in these sediments are relatively well understood, the diversity of heterotrophic organisms and their ecophysiologies remain largely unknown.

Giant tubeworms – Riftia pachyptila – that live in symbiosis with chemosynthetic microorganisms. The surrounding white layer are mats of sulfur-oxidizing bacteria. (Photo: WHOI)

To investigate these heterotrophic communities we joined an expedition to Guaymas Basin in December 2016 (AT37-06, chief scientist: Andreas Teske). With the help of the submersible Alvin we collected sediments on the seafloor and brought them back to the lab.

Robotic arm of Alvin taking a temperature measurement. On the right are cores to take sediment samples, water samplers are on the left (Photo: WHOI).

The projects is based on a large-scale cultivation experiment testing multiple combinations of carbon and energy sources using hydrothermal sediments of the Guaymas Basin. Each of the combinations should in theory enrich for a distinct community that is specialized on the provided conditions.

Fed-batch microcosms to enrich microorganisms using defined carbon sources and electron acceptors. Each condition selects for communities specialized on the provided “niche”. (Photo: E. Ruff)

We investigate these organisms – their ecology, physiology, and interactions – using stable isotope metaproteomics, metagenomics, and physicochemical measurements. We aim to understand the microbial populations, metabolic pathways and mechanisms of coexistence.

Scientific crew of RV Atlantis Expedition AT37-06 to Guaymas Basin. (Photo: A. Epp)

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