Meal Plans

Bacterial populations’ differing strategies for responding to their environment can set genetic routes to speciation.

Aug 1, 2014
Rina Shaikh-Lesko

SPLIT DECISION: Recently speciated marine bacteria use different strategies—biofilm growth (red) or mobility (blue)—to obtain nutrients.ILLUSTRATION BY YUTAKA YAWATA, GLYNN GORICK, AND ROMAN STOCKER


The paper
Y. Yawata et al., “Competition–dispersal tradeoff ecologically differentiates recently speciated marine bacterioplankton populations,” PNAS, 111:5622-27, 2014.

The background
Marine bacteria obtain nutrients from clustered particles that float in the resource-poor broth that is ocean water. Yutaka Yawata, a postdoctoral fellow in Roman Stocker’s lab at MIT, and colleagues wondered if differing strategies used by bacteria to secure these scarce nutrients could influence how populations adapt to their microenvironments and, ultimately, drive speciation, or whether speciation happens by more passive routes.

Diverging strains
Yawata and his team studied two recently diverged populations of Vibrio cyclitrophicus—labeled S and L—isolated from different depths in the same ocean region. They found the L population to be skilled at attaching to nutrient particles and developing into biofilms, whereas the S population could swiftly move to unexploited nutrient patches.  

The technique
The researchers used a microfluidic device to create chemical gradients that could be quickly altered to observe how the bacteria respond. They found that S bacteria responded much more quickly to changes in nutrient gradients, while L populations stayed attached to surfaces, where they created biofilms. “They are starting to become two different species on a genetic basis—and on a behavioral basis,” says Yawata.  

The implications
The finding demonstrates that bacteria can actively respond to their environment to secure resources and that they make strategic tradeoffs to do so, characteristics previously shown only in plants and animals. “Behaviors can actually play a role and be barriers to gene flow,” causing populations to diverge even at the microscopic scale, says marine microbiologist Linda Amaral-Zettler of the Marine Biological Laboratory in Woods Hole, Massachusetts.