The microbial community structure in a meromictic volcanic lake (Lake Averno, Italy)

Volcanic lakes are characterized by physicochemical favorable conditions for the development of reservoirs of greenhouse gases that can be dispersed to air during occasional rollover events. By combining a microbiological and geochemical approach, we showed that the chemistry of the CO2- and CH4-rich gas reservoir hosted within the meromictic Lake Averno (Campi Flegrei, southern Italy) are related to the microbial niche differentiation along the vertical water column. The simultaneous occurrence of diverse functional groups of microbes operating under different conditions suggests that these habitats harbor complex microbial consortia that impact on the production and consumption of greenhouse gases. In the epilimnion, the activity of aerobic methanotrophic bacteria and photosynthetic biota, together with CO2 dissolution at relatively high pH, enhanced CO2- and CH4 consumption. At Lake Averno, the chemical, isotopic and microbiological data consistently indicate a strong inter-dependence between the chemical features of the dissolved gas reservoir and the microbial community structure along the vertical water column.