Metabolism of CO and H2 by pioneer bacteria in volcanic soils and the phyllosphere

Trace gas degradation is a widespread metabolic adaptation in microbial communities, driving chemosynthesis and providing auxiliary energy that enhances persistence during nutrient starvation. In particular, carbon monoxide and hydrogen degradation can be of crucial importance for pioneering microbial communities colonising new, oligotrophic environmental niches, such as fresh volcanic deposits or the aerial interface of the phyllosphere. After volcanic eruptions, trace gas metabolism helps pioneer colonisers to initiate soil formation in ash deposits and on recently solidified lava, a vital ecosystem service. Similarly, in the phyllosphere, bacteria colonising newly emerging leaves and shoots, and/or persisting on the oligotrophic surface of plants, also benefit from trace gas oxidation and, given the global size of this habitat, likely constitute a significant sink for these trace gases affecting atmospheric chemistry. Herein, we review the current state of knowledge surrounding microbial oxidation of carbon monoxide and hydrogen and discuss how this may contribute to niche colonisation in oligotrophic ecosystems.