The present invention provides for a method to identify a second or mutant phosphomevalonate decarboxylase (PMD) with a higher PMD activity compared to a first PMD, comprising (a) culturing a medium comprising a first host cell expressing the first PMD and a second host cell expressing the second or mutant PMD wherein the first and second host cells have their respective PMD enzymatic activities coupled to the growth rates of the host cells, and (b) identifying the second host cell that has a higher growth rate than the first host cell, thereby identifying the second or mutant PMD having a higher PMD activity.