Unveiling microbial oxidizers in Chihuahuan Desert rock varnish (Mexico): a pioneer study

Abstract

Arid and semi-arid desert areas characterized by extreme conditions, including northern Mexico, have rocks with micrometric coatings. These coatings are known as desert varnish, an often dark-red microlayer deposited over millennia and developed on different rock types. These microlaminations, rich in clay minerals and Fe- /Mn-oxides, can serve as habitats for various microorganisms, mainly fungi and bacteria. However, the role of microorganisms in these varnish formations is still under debate. In the Chihuahuan desert (Mexico), particularly in the Samalayuca ridge, extensive areas are covered by rocks with desert varnish. Here we present a research effort focused on isolating Fe- and Mn-oxidising microorganisms in different culture media, along with directed sequencing. Using a benzidine spot test to detect oxidant species revealed the presence of bacteria and fungi inhabiting these layers. Likewise, we contribute to a better understanding of the formation of desert varnish, representing the first report of specific microorganisms isolated from rock vanish of the Chihuahuan desert.