New research sheds light on microbes’ evolution

Their find­ings were pub­lished Thursday in the journal Sci­ence. The paper—titled “Bio­geo­graphic pat­terns in ocean microbes emerge in a neu­tral agent-​​based model”—was co-​​authored by Ferdi Hell­weger, a micro­bial ecology expert and an asso­ciate pro­fessor of civil and envi­ron­mental engi­neering; his doc­toral stu­dent Neil Fredrick, PhD’15; and oceanog­ra­pher Erik van Sebille of Australia’s Uni­ver­sity of New South Wales.

Over the past sev­eral decades, ecol­o­gists have come to under­stand that both nat­ural selec­tion and neu­tral evolution—that vari­a­tion within and between species is caused by genetic drift and random mutations—play a role in the bio­geo­graphic pat­terns of ocean microbes.

In this study, Hell­weger et al. quan­ti­fied the role of neu­tral processes by sim­u­lating divi­sion, muta­tion, and death of some 100,000 indi­vidual marine bac­teria cells with full genomes in a global sur­face ocean cir­cu­la­tion model. They ran the model for up to 100,000 years and then ana­lyzed the output using advanced DNA align­ment algorithms.

Their results flew in the face of the long held notion that microbes are infi­nitely mobile—that the same cells could be found any­where in the world’s oceans, unhin­dered by geo­graphic bound­aries. On the con­trary, the researchers found that microbes evolve faster than the ocean cir­cu­la­tion can dis­perse them, leading to substantial—and dynamic— bio­geo­graphic pat­terns in their sur­face ocean pop­u­la­tion.

“Microbes differ between provinces because of neu­tral evo­lu­tion and dis­persal lim­i­ta­tion,” said Hell­weger, whose ongoing research on this topic is sup­ported by grants from the National Sci­ence Foun­da­tion and the National Oceanic and Atmos­pheric Admin­is­tra­tion. “Because provinces are not well-​​mixed, the dif­fer­ences can con­tinue to grow.”

What’s more, the find­ings shed light on how ocean microbes may respond to global cli­mate change. “You may not see microbes adapt to cli­mate change as rapidly if ocean microbes were com­pletely mixed and they were every­where,” Hell­weger posited. “Cer­tain species of microbes may not thrive under new tem­per­a­tures in cer­tain provinces.”

Up next: Hell­weger, Fredrick, and van Sebille will use a sim­ilar mod­eling approach to explore deep ocean microbes in addi­tion to envi­ron­mental selection.