CHEMOARCH

Identity and biogeochemical role of chemoautotrophic prokaryotes in aquatic ecosystems

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 Obiettivo del progetto (Objective)

'We aim to identify relevant aquatic chemoautotrophic prokaryotes, which can play a key biogeochemical role with the capacity to fix CO2 independently of light. Although severely underestimated, chemoautotrophy can be widespread in natural systems and it can importantly participate in carbon cycling. Chemoautotrophs are highly diverse at the phylogenetical and metabolical levels, but our knowledge about both aspects is still very limited and will be assessed in this project. Firstly, we will identify active chemoautotrophs through Stable Isotope Probing with 13CO2. By this approach, we will label and isolate the nucleic acids of aquatic chemoautotrophs with 13C, and identify them through appropriate molecular tools. Large inserts of the isolated genomes will be analysed in fosmid clone libraries, in order to find genes that can shed light to the metabolic fashion of these organisms. This is particularly relevant in order to establish links between chemoautotrophy and other biogeochemical processes. We will focus on a specific group, Crenarchaoeta, which grows chemoautotrophically and could play a key role in nitrogen cycle in marine waters, but has not yet been studied in freshwater/brackish systems such as the ones we will sample. Finally, a survey of distribution and activity of chemoautotrophs will be done by the combination of in situ hybridization with specific probes and microautoradiography with 14CO2. This will allow us to quantify the amount of active cells of different groups in CO2 uptake along environmental gradients (transcending the freshwater-coastal waters boundary), and evaluate their biogeochemical relevance in aquatic ecosystems.'

Introduzione (Teaser)

Marine microorganisms studied in the polar regions have provided valuable information about the role of the greenhouse gas carbon dioxide (CO2) in aquatic ecosystems.

Descrizione progetto (Article)

Carbon fixation enables CO2 gas from the earth's atmosphere to be converted into a solid compound by organisms known as autotrophs, which are able to produce their own food. The process is driven by photosynthesis, whereby CO2 is turned into sugars.

However, chemoautotrophic microorganisms can fix CO2 without the use of light. Although this process is widespread in natural systems and plays an important role in the carbon cycle, the fixation of CO2 in the dark has not been widely studied.

The EU-funded project 'Identity and biogeochemical role of chemoautotrophic prokaryotes in aquatic ecosystems' (Chemoarch) has investigated the process of dark CO2 fixation in aquatic systems by identifying chemoautotrophic microorganisms and studying their abundance and metabolic activity. Researchers have also examined the main factors that determine the distribution of the microorganisms in the environment.

The Antarctica and Arctic have been visited by Chemoarch scientists studying microorganisms known as Crenarchaeota, which belong to a group called Archaea. Although Crenarchaeota are abundant in the polar regions their diversity and ecology is mainly unknown.

Researchers have discovered that although most of the Crenarchaeota in Antarctic and Arctic waters are chemoautotrophs they fix less CO2 than expected. Scientists have found a wide range of Archaeans in different Antarctic water masses, indicating that environmental conditions influence their diversity.

Project partners have also identified Arctic marine bacteria that are active in dark CO2 assimilation. Results have indicated that this could be an important process for the metabolism and survival of polar bacteria.

The success of the Chemoarch project will help improve understanding of the biogeochemical role of Archaea in polar systems. Due to the great sensitivity of these environments to global climatic change, understanding mechanisms underlying the regions' biochemistry is a priority for scientists and policy-makers alike.