How gut bacteria thrive in humans

Production of inositol lipids by intestinal bacteria is unexpectedly widespread

A research team led by scientists from the Max Planck Institute for Biology in Tübingen has made significant progress in understanding how bacteria thrive in the human gut. Researchers studied how bacteria produce inositol lipids. These chemicals are essential for many cellular processes in humans and other eukaryotes, but have rarely been observed in bacteria. The results suggest that inositol lipids have effects on the symbiosis between bacteria and their hosts.

Microorganisms such as bacteria and fungi inhabit the human gut and participate in metabolism, the immune system, and other bodily functions. In order to understand the impact of the microbiome on humans, researchers are not only trying to determine which microorganisms are present in the gut, but also to elucidate the molecular mechanisms of interaction between the microbiome and the host. A research team led by scientists from the Max Planck Institute for Biology in Tübingen has now investigated how gut bacteria produce a group of substances known as inositol lipids, making a decisive step forward in our understanding of this interaction.

Inositol lipids regulate communication between cells and inflammation

Inositol lipids play an important role in many cellular processes in humans and most other non-bacterial organisms: they regulate how cells signal to each other, influence inflammatory processes, and help proteins find their proper site of action within the larger cell. An imbalance in inositol levels is associated with diseases such as polycystic ovary syndrome, the most common hormonal imbalance in women of reproductive age.

Unlike humans and other eukaryotes, for which inositol lipids are vital, bacteria produce them relatively rarely. A research team led by Ruth Ley, director of the Max Planck Institute for Biology in Tübingen, was now able to inositol lipid synthesis Bacteroides thetaiotaomicron describe a bacterium that is widely distributed in the colon and a popular model organism in microbiome research. By creating a hitherto undescribed strain of the species Bacteroides thetaiotaomicron developed, in which the production of inositol lipids can be controlled, were able to prove that these substances influence the physiology of bacteria. “Although we do not fully understand the precise role of inositol lipids in bacteria, we have observed that they are essential for successful growth in the host gut,” says Stacey Heaver, first author of the scientific paper. The team found inositol in the bacterial capsule, a layer that protects the bacteria from being engulfed by the host’s immune cells. In addition, inositol lipids alter resistance Bacteroides thetaiotaomicron against antimicrobial peptides, chemicals used by the host to fight pathogens.

Possible interactions

The researchers also described the metabolic pathways of inositol lipid synthesis, that is, the chain of chemical reactions that leads to the production of inositol lipids. They also identified another putative pathway by which the bacteria could synthesize inositol lipids. “Finding metabolic pathways is interesting because it allows us to predict which other microbes might make inositol lipids in the same way as our model organism,” explains Heaver. “With this knowledge, we may even be able to trigger or influence the production of inositol lipids.”

Heaver is excited about future research on whether and how bacterial inositol lipids might benefit the host organism: “It’s possible that there are interactions between bacterial lipids and mammalian host lipids,” she says. “We have made great progress in understanding the magnitude of such interactions.”

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