Rather than applying mass amounts of antibiotics to vats of biofuel-producing microorganisms to keep control these cultures, researchers have developed a new technique using modified strains that outcompete other possible contaminating microbes. The modified strains consume xenobiotic nutrients, which are not naturally produced or degraded by most microorganisms, so only the biofuel-producing microbes can use them to grow. The use of biofuels is poised as a more sustainable energy source compared to traditional, oil- or gas-based ones, yet mass production of biofuels remains challenging. For example, mass production of fuels from microorganisms would require cultivation in large reservoirs; if other microbes start growing in these carefully controlled reactors, it will negatively affect yield and productivity. In search for a solution, Arthur Shaw et al. sought to create strains of microbes that could outcompete other contaminant strains while still supporting biofuel production. They call this new technique: robust operation by utilization of substrate technology (ROBUST). First, the team engineered an Escherichia coli strain to use melamine as a nutrient, a substance not normally used by other bacteria. The modified strain quickly outcompeted a wild-type strain in melamine-rich cultures. The process also worked in two yeast species. The researchers modified strain of Saccharomyces cerevisiae to utilize cyanide and phosphite for nutrients. As well, a strain of Yarrowia lipolytica was modified to use phosphite. Both modified strains outcompeted their control counterparts in a cyanide and/or phosphite medium that was applied to cultures of sugarcane juice and wheat straw lignocellulosic hydrolysate, two broadly available industrial feedstocks. The authors note that several other types of potential biofuel products that could benefit from ROBUST, although further research is needed. A Perspective by Rebecca Lennen discusses this development in greater detail.