Identification of black varnish fungi of the Samalayuca desert, Chihuahua, Mexico

Abstract

Rock varnish is a thin mineral layer that forms on rock surfaces, it is commonly found in arid and desert environments. Rock varnish is mainly composed of clays, Fe and Mn oxides, and other elements such as Si, Al, Mg, Ca, Ba and Ce, among others (Dorn & Oberlander, 1981). Its formation depends on abiotic processes, such as variable mineral deposition cycles, and/or biological processes involving Fe and Mn mineralizing microorganisms. Black fungi are a polyphyletic group that are usually associated with rocks in arid areas. Several species have been found in desert varnishes, among which black fungi, also known as black desert fungi, belonging to the Ascomycota class (Gorbushina & Broughton, 2009). These fungi accumulate melanin in their wall, to protect themselves from UV radiation and other environmental stressors. Black fungi of the classes Alternaria, Cladosporium, Dothideomycetes and Eurotiomycetes classes have also been identified on desert varnishes (Sterflinger & Prillinger, 2001; Gorbushina & Broughton, 2009). In the northern desert of Mexico, the mountain range is mainly composed by sandstone that the potential to form and retain the varnish; and they also present associated black fungi (López-Ruiz et al., 2022). In this work, isolated five different fungi morphotypes from Samalayuca’s varnishes, Chihuahua were characterized microscopically and identified at the molecular level. The role of these species in the possible biological contribution to varnish formation will be discussed.