ARC Centre of Excellence in Synthetic Biology

Synthetic Biology


21, Feb 2024

Sweetener for the sugar industry

Nothing says northern Australia like fields of lush, waving sugar cane. Yet only a third of the tropical harvest becomes valuable sugar products. The rest is considered waste.

That 30 percent accounts for 95 percent of the A$2 billion a year revenue. The 70 percent of left-over wood and pulp – known as bagasse – currently has little economic value. But a team from the Centre’s Queensland University of Technology node aims to change that.

Francisco Peralta is part of a team hoping to produce higher-value commercial products using bagasse and a yeast called Yarrowia lipolytica.

‘Bagasse is a renewable source of energy and carbon for biodegradable plastic,’ he explains. ‘It is burned for energy – which is not very sustainable – or even to make bricks. However, none of these options offers significant added value.’

By using bagasse as a feedstock to grow microbes, pairing it with the yeast and putting it through a fermentation process, the economic return could be very different.

Microorganisms have the power to use simple sugars and bio-convert them into higher value products. Yarrowia lipolytica naturally produces about 20 percent of its total weight in lipids – fatty, waxy, or oily compounds that are soluble in organic solvents and insoluble in water.

With metabolic engineering, the team aims to boost that to 70 percent, and use the output to create products ranging from biodiesel to nutritional oils like Omega 3.

‘But to be able to do this we need to pre-treat the bagasse because it is made of sugar in a polymeric state that is hard to metabolise – like eating plastic instead of sugar,’ says Francisco.

‘Lignin materials – better known as wood! – are made from polysaccharides, mostly of chains of xylose and glucose. To break these chains we undertake a three-step treatment.’

‘This ends up giving three products: one that is mostly glucose, another xylose and the other glycerol. We want to be able to use all three to make the production sustainable.’

Once broken down, the three products are bioconverted by the yeast to bio oils.

‘We can enhance the yield of total lipids by precision fermentation by selecting the right conditions for lipid production for this host,’ says Francisco.

The team has proven that its engineered Yarrowia can use the pre-treated waste. The next step is to conduct more metabolic engineering to improve the yeast’s capacity to produce more lipids.

‘We are looking forward to producing specific products, instead of fatty acids in general. By means of – you guessed it – more synthetic biology and precision fermentation using our sugar-cane bagasse residues,’ says Francisco.

‘Adding value to an exciting renewable carbon source such as lignocellulosic bagasse is one more step towards a more sustainable and green future.’

Photo: Shutterstock