On the trail of mucus-eaters in the gut

March 5, 2013
This shows corresponding FISH (left) and NanoSIMS (right) analysis of gut microorganisms. Bacteroides or Akkermansia cells were stained with the aid of specific FISH probes. The amount of stable isotope 15N was analyzed in the same cells by NanoSIMS. The higher the 15N content of a cell, the more intestinal mucosa was taken up. White arrows point to cells that have taken up mucus. The Bacteroides cell marked with a green arrow has not fed on mucus. Copyright: Department of Microbial Ecology, University of Vienna.

The microbiology team of David Berry, Alexander Loy and Michael Wagner from the Faculty of Life Sciences, in collaboration with scientists at the Max F. Perutz Laboratories (University of Vienna and the Medical University of Vienna) and with the help of NanoSIMS technology, has for the first time succeeded in directly observing microorganisms feeding on the intestinal mucosa. The results of this research project appear in the current issue of the prestigious journal Proceedings of the National Academy of Sciences (PNAS).

To understand the research project by Michael Wagner and his team, one must be ready to follow the into the depths of mouse intestine. Michael Wagner, Professor for , provides this analogy: "Much like cows grazing in a meadow, can feed on mucus secreted by the mucosal tissue. There are a group of microorganisms that do not nourish themselves from mouse food, but rather are specialized in feeding on the secreted products of their host." The intestinal mucus layer is a vital barrier to block from entering the body and also plays a major role in . That is why scientists are very interested to know which bacteria inhabit the mucus layer in healthy organisms and thus may suppress the colonization and degradation of this barrier by pathogens.

The team led by Michael Wagner and Alexander Loy wanted to know as part of their activities supported by the Austrian Genome Research Program GEN-AU: Which organisms in healthy mice consider the mucosa and intestinal mucus layer a delicacy? "We've come up with an that allows us for the first time to look into the intestine and directly observe organisms grazing on the mucus and measure how much mucus they have taken up," said team leader Alexander Loy from the Department of Microbial Ecology, University of Vienna. To do this, the microbiologists in collaboration with the teams of Thomas Decker, Department of Microbiology, Immunobiology and Genetics at the Max F. Perutz Laboratories and Bärbel Stecher of the University of Munich, labeled an amino acid with stable isotopes that once in the bloodstream mostly ends up in the mucus. Wagner explains, "It became clear from the isotope ratio mass spectrometry measurements made by our collaborators Andreas Richter and Wolfgang Wanek from the Department of Terrestrial Ecosystems Research, University of Vienna, that after only a few hours the isotopes had arrived in the , where they were broken down by bacteria." A method was now established to identify bacteria feeding on the with single-cell resolution.

The key tool in the investigation was the high-resolution secondary ion mass spectrometry, or NanoSIMS for short. It is a device that cost more than 2 million euros and since its installation in February 2010 at the Faculty of Life Sciences at the University of Vienna has been in use by the team led by Michael Wagner for applications in microbiology and ecology. "This technology allows us to exactly quantify the amount of stable isotopes taken up by each microbial cell in a gut sample," says Arno Schintlmeister, who operates the unit at the Faculty.

"The investment costs for the NanoSIMS device were high, and it took some time before we were able to integrate this highly complex device completely in our research. Now however, our patience will be rewarded: The University of Vienna has the world's first study in which one does not have to indirectly infer the function of individual intestinal bacteria cells but can measure it directly", said microbiologist Michael Wagner This research approach has great potential and is a topic that will continue to be a research priority in the working groups led by David Berry and Alexander Loy in the coming years.

The bacterial cells measured by NanoSIMS facility were identified using fluorescence in situ hybridization - FISH for short - in the confocal laser-scanning microscope. "We have identified a number of mucus-eating microorganisms and clearly the most important players are Akkermansia muciniphilia and Bacteroides acidifaciens," explains Wagner, "The gut microbiota is a very hot research topic worldwide because the composition of our gut microbial communities appears to correlate with many diseases – from obesity and autism to inflammatory bowel disease."

Explore further: Bacteria enter via mucus-making gut cells

More information: Host-compound foraging intestinal microbiota revealed by single-cell stable isotope probing. From: David Berry, Bärbel Stecher, Arno Schintlmeister, Jochen Reichert, Sandrine Brugiroux, Birgit Wild, Wolfgang Wanek, Andreas Richter, Isabella Rauch, Thomas Decker, Alexander Loy und Michael Wagner. In: Proceedings of the National Academy of Sciences (PNAS), March 2013. DOI: www.pnas.org/cgi/doi/10.1073/pnas.1219247110

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