However, swimming is energy-intensive so motile bacteria swim only when it is worth the effort in terms of pay-back.
Some bacteria can also detect and respond to chemicals dissolved in the surrounding water, an ability known as chemotaxis.
The researchers compared the activity of motile and non-motile bacteria across environments that differed in levels of water movement and nutrient availability.
All water moves, but the extent of its turbulence varies widely in the ocean.
Wind and waves strongly churn the water near the surface, while the level of turbulence is much lower in the deep ocean, says Stocker.
The results show that the organic matter excreted by phytoplankton is patchy in the ocean, and is not as uniform as had been thought.
Organic matter enters water in bursts, after which a natural mixing and stirring action comes into play and the organic matter is dispersed.
The patterns of dispersal depend on the strength of turbulence and the extent of stirring and mixing.
"When you pour cream into coffee and stir it carefully, you get swirls of cream," says Taylor.
"Something similar happens when bursts of organic matter enter gently moving water. The swirls of organic matter are easily accessed by swimming bacteria which surround and absorb it.
"If you mix cream into your coffee vigorously, it quickly becomes evenly dispersed. When this happens in the ocean, the swimming bacteria have less to gain in seeking out the thinly-dispersed organic matter."
Bacteria get energy from organic matter--but they also expend energy in swimming.
"Our research suggests that the optimum environment is one of intermediate turbulence intensity--when bursts of organic matter are stirred into thin filaments that can be exploited by large numbers of bacteria," says Taylor.
"The best environ
|Contact: Cheryl Dybas|
National Science Foundation