Sweet discovery in leafy greens holds key to gut health

A critical discovery about how bacteria feed on an unusual sugar molecule found in leafy green vegetables could hold the key to explaining how ‘good’ bacteria protect our gut and promote health.

The finding suggests that leafy greens are essential for feeding good gut bacteria, limiting the ability of bad bacteria to colonise the gut by shutting them out of prime gut ‘real estate’.

Researchers from Melbourne and the UK identified a previously unknown enzyme used by bacteria, fungi and other organisms to feed on the unusual but abundant sugar sulfoquinovose – SQ for short – found in green vegetables.

Each year, leafy green vegetables – such as spinach – produce the sugar on an enormous scale globally, comparable to the world’s total annual iron ore production.

The research, published today in the journal Nature Chemical Biology, was led by Professor Spencer Williams from the University of Melbourne's Bio21 Institute, Dr Ethan Goddard-Borger from the Walter and Eliza Hall Institute and Professor Gideon Davies from the University of York, UK.

Professor Williams said we now know how bacteria extract the sugar from plants in order to fuel their growth.

“We discovered the enzyme YihQ, which is used by bacteria to absorb and metabolise these sulfur-containing sugars as food,” he said.

“Sulfur is critical for building proteins, the essential components of all living organisms.

"SQ is the only sugar molecule which contains sulfur, and ‘digestion’ of the molecule by bacteria releases sulfur into the environment, where it re-enters the global ‘sulfur cycle’ to be reused by other organisms.”

Professor Williams said that the pathway was unusual, but abundant in biological organisms.

Dr Goddard-Borger said the discovery could be exploited to cultivate the growth of ‘good’ gut bacteria.

“Every time we eat leafy green vegetables we consume significant amounts of SQ sugars, which are used as an energy source by good gut bacteria,” he said.

“This work answers a 50-year mystery that has surrounded how sulfur – an element that is essential for life on Earth – was used and recycled by living organisms."

The discovery also provides crucial insights that may one day be exploited to develop an entirely new class of antibiotics, Dr Goddard-Borger said.