The nitrogen and carbon cycles have been studied for decades and were assumed to be complete. Some reactions, although thermo­dynamically possible, were believed not to exist in nature. Most notably, microorganisms were not supposed to oxidize methane or ammonium without oxygen. This notion changed when the microorganisms for sulfate dependent anaerobic methane oxidation (AMO) and nitrite dependent anaerobic ammonium oxidation (anammox) were identified some 10 years ago.  Both anammox and AMO turned out to play an important role in the global nutrient cycling. At the moment, it is estimated that anammox is responsible for up to 50% of marine nitrogen loss, and that AMO even accounts for up to 90% of marine methane oxidation. The presence and activity of anammox bacteria and AMO consortia has been determined using nutrient profiles, fluorescently labelled RNA probes, ¹⁵N and ¹³C tracer experiments, and the distribution of specific anammox and archaeal membrane lipids in many different ecosystems. Both anammox bacteria and AMO organisms grow very slowly and are thus difficult to cultivate. Anammox bacteria have been enriched since the late 1990s, and nitrate/nitrite dependent AMO organisms are in culture only since last year, but none of the organisms are available in pure culture, yet. Recently, the environmental genomes of the anammox bacterium Kuenenia stuttgartiensis and the ANME-2 group were elucidated. From these genomes it has become clear that K. stuttgartiensis is a very versatile bacterium. It is able to use manganese and iron as alternative electron acceptors in addition to nitrate and nitrite. Also, K. stuttgartiensis and other anammox bacteria can use organic acids (formate, acetate and propionate) as additional energy source. With these properties the anammox bacteria may link the biological nitrogen cycle to the carbon and metal cycles in new ways. Further, anammox bacteria have an intriguing cellular architecture, currently under investigation using electron tomography, possessing a prokaryotic organelle bounded by a bilayer membrane containing unique ladderane lipids. These recent discoveries together with the notion that aerobic ammonium oxidation may be mediated by crenarcheota have shown that microbial conversions in the element cycles still are largely unexplored and will be a very exciting topic for future research.