Characterisation of the first actinobacterial group isolated from a Mexican extremophile environment.

The "Cave of Crystals" (aka 'Naica') in Chihuahua Mexico is a natural unique subterranean ecosystem which mainly consists of crystals made of calcium sulfate. The main system of caves are found at a depth of 300 meters (m) below sea level with crystals that range in size from a few centimeters to 15 m. The crystals date from nearly 400,000 years old and are thought to be formed when the cave was fully covered by water. At present time, this place shows a nearly constant temperature of 55 °C over the year and a humidity of 100 % which makes this place incomparable and unbearable to animal and/or human life. In the present study, two actinobacterial groups were isolated from within this system of caves and subjected to a systematic study to establish their phylogenetic relationship to microorganisms belonging to this vast group of Gram positive bacteria. Phenotypic properties, chemotaxonomic and 16S rRNA gene sequencing show that the microorganisms are members of the family Pseudonocardiaceae and are most closely related to the genus Prauserella. The present study is the first to report the isolation and presence of Actinobacteria or any other microbial form of life in this exceptional place. Moreover, this unexpected biodiversity can also provide an insight of the antibiotic resistome present in the isolates reported in this study.