Pigments that can do more

(Press-News.org) Anaerobic bacteria – masters of survival without oxygen Anaerobic bacteria were among the first life forms on earth and existed at a time when there was no oxygen in the atmosphere. While many organisms depend on an oxygen-rich environment to survive, anaerobes thrive in places where others cannot – in completely oxygen-free habitats such as the human gut or the ocean floor. The enzymes of these bacteria are even sensitive to oxygen. Their remarkable adaptability is increasingly attracting the attention of researchers.

Anaerobic bacteria often produce unusual substances. This makes them particularly interesting for research and biotechnology, for example for the production of antibiotics or biofuels. They are also indispensable players in the natural nutrient cycle by breaking down organic material such as cellulose and releasing nutrients back into the ecosystem.

A signal substance with a key role Clostridium thermocellum is one of the best-known anaerobic microbes when it comes to the degradation of cellulose – the main component of plant cell walls. It converts cellulose into sugar, which can then be used to produce biofuels such as ethanol. A conspicuous yellow pigment produced by the bacterium (YAS – Yellow Affinity Substance) plays a key role in this process. YAS preferentially attaches itself to cellulose fibers. It is assumed that YAS helps to direct the degrading enzymes precisely to where cellulose is present.

Structural analysis of bacterial pigments Researchers at the Leibniz Institute for Natural Product Research and Infection Biology – Hans Knöll Institute (Leibniz-HKI) and the Max Planck Institute for Chemical Ecology in Jena have now succeeded for the first time in elucidating the molecular composition of YAS. The scientists discovered that YAS consists of several components, so-called celluxanthenes, and determined their molecular structures using spectroscopic analyses (NMR, MS) and isotope labeling experiments. In addition, they identified the biosynthetic gene cluster responsible through targeted genetic manipulation.

A pigment with medical potential? Surprisingly, the pigments show an effect against certain microorganisms. The celluxanthenes have mild antibiotic activity against Gram-positive bacteria – including clinically relevant, resistant pathogens. Understanding the genetic basis of biosynthesis also opens up the possibility of producing or modifying celluxanthenes in the future. First authors Keishi Ishida and Jana Krabbe see promising results: “Although the yellow pigments have been known for almost a century, their structure has remained a mystery until now. We can now begin to investigate possible ecological functions, including antibacterial activity to defend the food source (cellulose) against competitors.”

A step towards a sustainable future The discovery and characterization of celluxanthenes bridges the gap between our understanding of microbial metabolism and practical applications in the energy sector – and perhaps in future medical research. The findings could also help to optimize the use of plant biomass.

The research is part of the “AnoxyGen” project, for which Christian Hertweck was awarded one of the prestigious ERC Advanced Grants from the European Research Council. Hertweck is head of department at the Leibniz-HKI and professor at the Friedrich Schiller University Jena. “AnoxyGen aims to unlock the hidden potential of anaerobic bacteria to produce new bioactive natural products,” explains Hertweck. “Many of these microorganisms carry genes in their genome for the production of valuable compounds, but these usually remain inactive under standard laboratory conditions.” The team is developing new molecular biological methods to activate these hidden biosynthetic pathways – methods that previously existed mainly for aerobic (oxygen-dependent) microbes. The aim is to discover and harness previously unknown natural substances with medical or biotechnological value. AnoxyGen combines modern synthetic biology with the discovery of active substances and could open up new possibilities for pharmaceutical development.

The AnoxyGen project also contributes to the Cluster of Excellence “Balance of the Microverse”, which investigates the complex signaling and communication mechanisms within microbial communities that govern life on Earth.

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