Most anaerobes work slowly

So far, there has been no real explanation for why bacteria have not devoured the oil reservoirs over the millennia. It is possible that some oil reservoirs were very hot and therefore remain almost free of bacteria to this day. In other cases, it is clear that bacteria have been at work. The tiny things are gourmets. From the hundreds of different alkanes present in crude oil, they look for the ones that are easier to digest, such as hexadecane, a molecule comprising 16 carbon atoms.

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Many bacteria break down dead plancton into water and carbon dioxide using oxygen. On the anoxic seafloor, anaerobes... [more]

Many bacteria break down dead plancton into water and carbon dioxide using oxygen. On the anoxic seafloor, anaerobes decompose a further part of the organic material using sulfate; creating hydrogen sulfide and carbon dioxide. What is left is converted into oil and gas in the seabed. Around natural oil sources, anaerobes also feed on oil constituents. [less]

Many bacteria break down dead plancton into water and carbon dioxide using oxygen. On the anoxic seafloor, anaerobes decompose a further part of the organic material using sulfate; creating hydrogen sulfide and carbon dioxide. What is left is converted into oil and gas in the seabed. Around natural oil sources, anaerobes also feed on oil constituents.

© MPI for marine Microbiology

© MPI for marine Microbiology

If such an oil sample is analyzed using a gas chromatograph, a device that can trace specific substances, it becomes clear that certain alkanes are missing. The varying properties and qualities of crude oil from different reservoirs may, in part, be due to the “feeding habits” of the anaerobes.

People who work with anaerobes need a lot of patience. Many anaerobes belong to the “sloths” of the microorganisms. They grow and reproduce in slow motion. Nobody is quite sure why this is. In contrast, the famous labo ratory bacteria Escherichia coli, the biotechnologists’ workhorse, is a true sprinter. It stays alive and functions using oxygen. When in good shape, it splits once every 20 minutes. In 10 hours, one such bacterium creates billions of successors.

In that period, Widdel’s bacteria have not even started growing. They may take days or weeks to split. “They live and die slowly,” says the scientist. This makes growing such microbes a tedious task. Microbiologists aim to create pure bacteriological cultures of bacteria to understand their function. However, a sample of water or sediment contains a whole host of different bacterial strains. In order to find the exact bacterial strain that degrades the oil in this microscopic soup, the sample is diluted over and over until, finally, statistically speaking, only one bacterium is left floating in the laboratory receptacle.

During this process, the bacteria must keep reproducing so that the scientists can establish whether there are still any oil-degrading bacteria left in the diluted sample. This takes time. So much time that, Widdel says, in the first years, he was rarely able to get even a doctoral student to work on his oildegrading anaerobes. Thus, for a long time, the dilution series was more of a side job for him and his colleagues.

The team in Bremen has now managed to isolate a range of pure strains, but so far they have not found a real winner among the anaerobes. These bacteria are simply not good enough to clean up a major oil spill, according to the scientists. They are much too slow. In cases of oil tanker damage or accidents like the one in the Gulf of Mexico, thousands of tons of crude oil are spilled in a matter of days. Against such volumes, even the quick aerobes, the oxygen-devouring cousins, are powerless. The tide brings the oil and tar masses onto the shore, where often lumps of oily mud and sand form. Widdel’s bacteria are active wherever the oxygen becomes scarce, for example underneath the black oil layers on the beach, or in places where oil seeps naturally from the seafloor, or in the oil reservoirs.