Archaea in microbial ecosystems associated to minerals in Andean Wetlands: a source of biodiversity and alternative geochemical cycles

Abstract

Atacama´s lakes are extreme environments where microbial diversity develops associated to minerals, (biofilms, microbial mats, microbialites and endoevaporites). All of them are highly productive systems developing under extreme conditions. Diversity is dominated by Archaea and bacteria which rubisco fijation of C would be precluded. The arising question is how do they obtain energy? How do they fix C? The answer could be in alternative pthways to fix C different than Calvin cycle and in the relationship among As and bacteria. In that way, As(III) has been proposed as an ancient source of energy used by the last universal common ancestor (LUCA) based on As(III) oxidase phylogenetic analysis. In the multi-extreme Lake at Volcano Galan (4650 m), a red biofilm was found. It was composed mainly by Haloarchaea (93%). Metagenomic analysis indicated a high abundance of As(III) oxidases (Aio) and respiratory As(V) reductases (ArrA) coded by Haloarchaea. Phylogenetic analysis supported a pre-LUCA hypothesis. A pure culture of an Halorubrum strain obtained from this biofilm, showed the presence of aio and arrA genes and grew better in the presence of As (III) transforming it to As(V) indicating its functionality. Our results demonstrate, for the first time, that Haloarchaea, respire As through As(III) oxidation and give a strong support to the use of As(III) as a primary source of energy in early forms of life.