sciencedaily | The human gut is home to thousands of bacterial species, most of
which have never been described in science. This ecosystem is a complex
living community: The microorganisms live side-by-side, compete for
nutrients, overthrow one another or even benefit off each other.
It is the aim of Almut Heinken, research associate in Ines Thiele's
workgroup, to understand these interactions more completely: "For my
thesis, I worked with data from literature and modelled on the computer
how certain bacterial species respond to one another when the living
conditions in their environment change," the scientist says. "Such
models are a common method for making better predictions about the
interactions of bacteria. We developed the method further and applied it
for the first time to gut bacteria. With eleven species, we were able
to calculate how they behave pairwise in the presence of human small
intestinal cells."
Almut Heinken discovered some surprising types of behaviour in these
studies: "Bacteria that are otherwise very dominant and overthrow other
species suddenly enter a symbiosis with those same species if, for
example, the oxygen content in the environment drops. They emit
substances that make it easier for otherwise outcompeted species to
survive. And they, too, receive substances they wouldn't get enough of
under the unfavourable living conditions." Heinken has calculated such
symbiotic behaviour for the bacterial species Lactobacillus plantarum,
for example.
This turnaround in metabolism is vital for the bacterial community to
continue functioning within the different sections of the gut: For
example, the oxygen content varies in different places along the small
intestine. There is more oxygen on the walls than in the centre, and
more at the start of the small intestine than at its end. "By the
bacteria mutually supporting one another when they find themselves in a
low-oxygen environment, the bacterial community remains functional as a
whole -- and so the digestion as well," Almut Heinken explains. The
nutrient supply and the presence of sloughed intestinal cells also
undergo great spatial variance, and have an influence on the symbiotic
behaviour of the bacteria.
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