Problems with oil platforms and tankers keep causing large amounts of oil to accidentally end up in the world's oceans. A study now shows which tricks oil-eating bacteria use to metabolize crude oil as quickly and effectively as possible. Accordingly, they form biofilms around individual oil droplets and ensure that the enclosed droplet forms finger-like protuberances. The increased surface allows more bacteria to attack at the same time. The findings help to better understand the role of bacteria in cleaning up oil slicks.
An explosion on the Deepwater Horizon oil platform in the Gulf of Mexico in 2010 resulted in one of the worst oil spills in history, spilling about 800 million liters of crude oil into the sea. But leaks on oil platforms and tankers also repeatedly lead to serious environmental pollution, most recently in July 2023 again in the Gulf of Mexico. To combat the oil spill, most of the oil floating on the surface of the water is pumped out or burned as much as possible. If this is not possible, so-called dispersing agents are used, which work in a similar way to soap and break up the oil slick into smaller droplets, making it more exposed to weathering and natural degradation. In this context, bacteria that can metabolize crude oil also play an important role.
Biofilm deforms oil droplets
One of these bacteria, called Alcanivorax borkumensis, has now been examined more closely by a team led by Manoj Prasad from the University of Tsukuba in Japan. "We have developed a microfluidic device that allows us to capture numerous oil droplets covered with bacteria and image them in real time," reports the team. "This platform allows us to capture the full dynamics of biofilm development, from single bacteria to complete consumption of the oil droplets." were exposed. While bacterial cultures that had only been in contact with the oil for a day needed around 72 hours to break down at least 90 percent of a new drop of oil, it took cultures that had previously had five days to get used to the oil to just about 72 hours 20 hours.
In search of the causes, the research team examined the shape of the biofilm more closely. The result: "When sampling after one day, A. borkumensis formed a spherical biofilm that grew outwards over the oil, and the oil drop remained largely spherical while it was consumed," reports the team. "In contrast, bacteria from a five-day-old culture develop a thin biofilm that deforms the oil droplet so that it forms protuberances and thus offers a larger surface for the growing number of bacteria to attack." So the metabolism rate of each individual bacterium remains the same, yes the deformation allows more bacteria to consume the oil at the same time.
As the oil breaks down, this so-called dendritic biofilm becomes more deformed, eventually breaking up into tiny fragments surrounded by bacteria. In the case of spherical biofilm, on the other hand, the droplets only become smaller and smaller, so that fewer and fewer bacteria are able to attack them and degradation slows down over time.
Complex interactions still unclear
In the open sea, oil slicks are often difficult for bacteria such as A. borkumensis to attack because they form a closed cover. The natural waves only partially ensure that individual droplets form, which can be better broken down. Added dispersing agents should take over this task. To test the effect of such agents, Prasad and his team mixed some of the bacteria-oil mixtures with a substance that is very similar to commercial dispersants.
But instead of helping to break it down, the agent had the opposite effect, at least in cell culture: within four hours, it washed the oil off the biofilms, and the previously deformed oil droplets assumed a spherical shape again. However, it is still unclear what this means for real use. "Although we have found that the addition of oil dispersants compositionally similar to commercial blends results in rapid detachment of the biofilm from the oil droplets, numerous factors such as dispersant concentration, oil composition, temperature and pressure are likely to influence as well nutrient concentrations affect biodegradation,” the team writes.
It should also be noted that A. borkumensis is not the only bacterium involved in oil degradation. “Alcanivorax borkumensis alone cannot break down the thousands of hydrocarbons in crude oil. This requires a diverse community of microbes that interact and sometimes compete with each other," write Terry McGenity and Pierre Laissue of the University of Essex in a commentary on the study, also published in the journal Science. In order to better understand the spread and biological degradation of crude oil in the oceans, further studies are necessary that take the complex interactions into account.
Source: Manoj Prasad (University of Tsukuba, Japan) et al., Science, doi: 10.1126/science.adf3345