As it turned out, this hypothesis was plausible, but incorrect. Friedrich Widdel brought water with oil residue from the tanks to the laboratory and placed it in air-tight containers. Then he waited. Sure enough, slowly but surely, hydrogen sulfide formed in the test tube. The only possible source was the degradation of the crude oil using the sulfur compound sulfate. To this day, scientists have only partly understood what happens in the metabolism of bacteria. Widdel is thus also trying to find the proteins that are involved in degradation.
It looks as if the anaerobes first extend the chains and then pick them apart, piece by piece, in order to finally respire them. Instead of oxygen, the anaerobes use, for example, sulfate, which is present in much higher concentrations in seawater than oxygen. Even if the oxygen in the oil separator tank has been used up, the anaerobes can still find quite a lot of sulfate. The end product of the reaction of the sulfate with the alkanes, through a complex sequence of metabolic processes in the bacteria, is hydrogen sulfide. To reduce these and other undesirable bacteria in oil production, antibacterial substances are added to the water, which is pumped into the reservoir.
At first, many thought that this theory of anaerobic degradation of alkanes and oil was too far-fetched. Widdel had to substantiate his findings – it was, after all, plausible that the oxygen had been able to slowly penetrate the rubber plugs of the tightly sealed bacterial containers. There is no such thing as a 100-percent-tight rubber or plastic part. “So we put our oil samples in small glass phials, which we sealed,” Widdel says, smiling. More air-proof than that isn’t possible. In this way, he managed to get the final proof: the alkane chains are degraded anaerobically to carbon dioxide, and the sulfate is converted to hydrogen sulfide!