Symbiosis means "living together", i.e. when two organisms live in close association to benefit each other. For instance, soil bacteria called rhizobia, like Bradyrhizobium diazoefficiens, can enter into symbiosis with leguminous plants, like soybean. In this relationship, the plants provide the bacteria with a food source and the bacteria provide the plant with the essential nutrient nitrogen. Our recent research suggests that hopanoids or cholesterol-like lipids produced by rhizobia are required for proper growth of bacteria in both free-living soil and symbiotic plant states. More research into how hopanoids help bacteria to survive may aid in engineering of more robust agricultural strains that are resistant to harsher climates.