A Very Special Large Prokaryote
Meet the beggiatoa. Since he's a chemolithotroph, he loves sulfur (or brimstone, if you prefer!) and while he's a pain to confront if you're managing a sewage treatment, industrial waste plant, or a decaying seaweed bed, he can detoxify all the hydrogen sulphide in your soil. Just don't think it'll be pretty--the oxidation produces a pale, stringy deposit known as sulfur sludge. Beggiatoa are famous for causing "bulking," in which a sludge mass thickens in volume but not in weight. Fully activated "bulking sludge" creates a real problem for purification plants, but despite all this, beggiatoa still managed to land a "Microbe of the Week" slot back in '99.