 The long @-@ term evolution experiments using E. coli , begun by Richard Lenski in 1988 , have allowed direct observation of major evolutionary shifts in the laboratory . In this experiment , one population of E. coli unexpectedly evolved the ability to aerobically metabolize citrate , which is extremely rare in E. coli . As the inability to grow aerobically is normally used as a diagnostic criterion with which to differentiate E. coli from other , closely related bacteria , such as Salmonella , this innovation may mark a speciation event observed in the laboratory . 
