A new technique gives bio-fuel producing microbes the upper hand against unwanted invaders. The development could reduce the cost and environmental impact of producing liquid bio-fuels as alternatives to petroleum-based products, thanks to a new metabolic engineering technique. Liquid bio-fuels are increasingly used around the world that helps reduce carbon emissions. The fuels are often produced using microbes to convert sugars from corn, sugar cane or cellulosic plant mass into products such as ethanol by fermentation.