 This tendency of microbiology to pervade and transform other fields is a hallmark of the science’s development. Molecular microbiology, a product of the mid-twentieth century, amply illustrates this trend. Following the successes of germ-theoretic accounts of microbes and disease, microbial biochemistry flourished as microbiologists focused on the precise causal pathways by which microbes achieved their effects (whether in hosts or other environments). The laboratory tractability of microbes and versatility of their metabolic accomplishments gave rise to a vast experimental literature on bacterial biochemistry (e.g., Kluyver 1936; Stephenson 1939). In the 1940s, this background lent itself to the emerging field of what became molecular biology, in which all the initial major discoveries were made in microbial systems. The bacterium Escherichia coli (E. coli) in particular had epistemic