Alternative oxidase gives Ciona colonists a head start in rotten egg water.
This article explains how invasive creatures such as the sea squirt Ciona intestinalis thrive in habitats rich in toxins such as hydrogen sulphide through an adapted enzyme called 'alternative oxidase', allowing them to produce the energy they require to survive in the presence of toxic hydrogen sulphide gas. The article studied how toxic the dissolved gas is for freshly fertilized sea squirt eggs for them to invade these kinds of habitats, that even with their specially adapted hydrogen-sulphide-proof alternative oxidise, the young were only able to survive reasonably well in hydrogen sulphide concentrations of up to 15 µmol l-1. With this, it was needed to confirm whether the embryos' alternative oxidase provided them with their resistance to the toxin, or whether they were resorting to another strategy to survive the poison. Without the key enzyme, their survival plummeted by 81% to 12%. However, when provided with an additional source of alternative oxidase, their survival rate returned to 27%. In addition, the study measured whether the embryos were activating the gene responsible for the essential enzyme - and therefore likely to be producing the alternative oxidase - while developing in 15 µmol l-1 hydrogen sulphide, and it was clear that they had increased expression of the gene to combat the toxin. Their alternative oxidase source of energy is the key to the youngs' survival when their water reeks of rotten eggs.