Oil Dispersants Hinder Oil-Degrading Bacteria

Remember the Deepwater Horizon oil spill?  Researchers at the University of Georgia found that chemical dispersants meant to help oil-munching microbes break down oil may have the opposite effect.

The Deepwater Horizon spill spewed nearly 750 million liters of oil into the Gulf of Mexico, and nearly 7 million liters of chemical dispersants were used to clean it up.  Dispersants contain surfactants such as sodium lauryl sulfate that break up oil into small droplets.  Dispersants decrease the amount of oil that makes it to shorelines and may make oil more readily available to microbes for degradation.  
   
The group collected samples from the Gulf of Mexico and treated them with oil, dispersant, or a combination of the two.  They characterized the abundance of Colwellia and Marinobacter.  Species of Colwellia are capable of degrading both hydrocarbons (oil) and dispersants, while Marinobacter mainly degrade hydrocarbons.  Both thrive in cold, deep waters.

Dispersant and dispersant/oil-treated samples increased the abundance of Colwellia from 1% to 26-43%, while its abundance remained low in samples treated with oil alone. On the other hand, Marinobacter increased in abundance from 2% to 42% in oil-treated samples, but remained low in samples treated with dispersant or dispersant and oil.  These results suggest that dispersants applied during the Deepwater spill may have enriched for dispersant-degrading bacteria instead of stimulating the growth of oil-degrading species.

According to study author Samantha Joye, “the fact that dispersants drove distinct microbial community shifts that impacted oil degradation efficiently came as a big surprise … it is critical to quantify the factors that influence the efficiency of oil biodegradation in the environment, and that includes dispersants”.
 
Sources: PNAS, Science Daily, MicrobeWiki, Wikipedia