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From toxic waste to beneficial nutrient, a new look at acetate

Du déchet toxique à un nutriment bénéfique, nouveau regard sur l’acétate

Microorganisms such as bacteria use preferentially sugars to grow. In this process, they produce waste products such as acetate that inhibits their growth. Acetate has long been considered toxic to bacteria until teams from the Toulouse biotechnology institute laboratory (TBI - INRAE / INSA Toulouse / CNRS) demonstrated that, far too be toxic, acetate is in fact a beneficial nutrient under conditions frequently met by E. coli in its natural and industrial environments.

Published on July 13, 2023 on INRAE website

Acetate, first and foremost a "toxic waste" ...

Glycolysis is a set of biochemical reactions that take place inside the cells to convert sugars into energy and building blocks for cellular growth. Glycolysis is found in all living organisms, whether they are multicellular (like us humans) or unicellular, like bacteria.

When bacteria have large amounts of sugars at their disposal, they use them rapidly to ensure the fastest possible growth. In such conditions, glycolysis leads to the secretion of fermentation products like acetate (which gives its characteristic smell to vinegar for example). Acetate production is notably observed in the bacterium Escherichia coli (naturally present in our digestive tracts) and annoyingly produced in the many biotechnology processes exploiting this bacteria for the industrial production a broad range of molecules of interest (drugs, bioplastics, etc.).

Indeed, scientists have observed that acetate was toxic to bacteria, in particular inhibiting their growth. Despite decades of research on this topic, the causes of acetate production remain poorly understood, especially why the bacterium produces a molecule that is eventually harmful to itself.

... Which turns out to be a beneficial nutrient for bacteria

Despite its known negative impact on Escherichia coli growth, a new study published in The EMBO Journal has shown that acetate is much more than just a waste product. Indeed, acetate can also be a beneficial nutrient for bacterial growth in some conditions.

This is particularly true when the utilization of sugars by glycolysis is less efficient, for example because sugars are less accessible in the environment. Escherichia coli then compensates for this reduction in sugars utilization by simultaneously using acetate to produce energy and boost its growth. So, far from being toxic, acetate is actually beneficial to Escherichia coli growth. The two teams have also shown that the same genes are involved in acetate production and consumption and are thus responsible for its dual role as a toxic waste product or beneficial nutrient.

A sustainable resource for environmentally friendly biotechnology

This work sheds new light on the mysteries of producing molecules previously considered as "toxic wastes" for the cells. It also paves the way for better exploitation of acetate as a sustainable resource for biotechnology. Acetate is present in various plant-derived nutrients and can be obtained from CO2. A better use of acetate by E. coli could therefore improve the sustainable bioproduction of many molecules of interest, such as biodegradable plastics, while reducing the environmental footprint of biotechnology.

References :

Millard P. et al. (2023). Acetate is a beneficial nutrient for E. coli at low glycolytic flux. The EMBO Journal. e113079.

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