Trace Elements of methanogens in an astrobiological context

Trace elements represent just a small part in the volume of a standard growth medium. These micronutrients are necessary for supporting the growth and metabolism of all life forms. The present study focuses on hydrogenotrophic methanogens. For these anaerobic microorganisms, trace elements are of particular importance due to their usage of the archaeal version of the Wood-Ljungdahl pathway. This pathway might be used by the last universal common ancestor in a hydrothermal vent setting. However, studies on the physiology of pure cultures of methanogens growing on H2/CO2 showed that the required optimal concentration of trace elements for microbial microorganisms is much higher than in the natural environments . The level of some trace elements in natural anoxic waters was even found to be below the concentration required for growth of methanogens in pure cultures. In this study, we investigate the effects of varying trace element concentrations on the growth of the two hydrogenotrophic methanogenic strains Methanothermobacter marburgensis and Methanothermococcus okinawensis. When varying the amount of trace elements the productivity and physiology of the two tested methanogens could be altered.