The bacteria she and Valentine saw in the deep-water samples in May and June were related to types of psychrophilic, or cold-loving bacteria.
"Most bacteria grow more slowly at cooler temperatures -- that's why we keep our food in the refrigerator," said Redmond. "But psychrophilic bacteria actually grow faster at cold temperatures than they would at room temperature."
To provide additional evidence of the importance of temperature, the scientists added oil to water from the Gulf, and incubated it at 40 F and at room temperature (about 70 F). They looked at which bacteria grew at the different temperatures.
In the 40 F samples, Colwellia were most abundant, but were only found in low numbers in the room temperature samples, suggesting that the bacteria have an advantage in cold water.
"To figure out which bacteria were consuming methane, ethane, and propane, we used a technique called stable isotope probing, in which we incubated fresh seawater samples from the Gulf with isotopically labeled methane, ethane, or propane," Redmond said.
The bacteria that grew as they consumed the methane, ethane or propane converted the labeled gases into biomass, including their DNA. By sequencing the DNA, the scientists were able to identify the bacteria.
The bacteria that consumed the ethane and propane were the same Colwellia in the samples from May and June, when ethane and propane consumption rates were high. They were abundant when the researchers incubated oil at 40 F, but not at room temperature.
This suggests, say Valentine and Redmond, that the Colwellia grow well at low temperatures, and can consume ethane and propane.
"The ability of oil-eating bacteria to grow with natural gas as their 'foodstuff' is important," said V
|Contact: Cheryl Dybas|
National Science Foundation