NUTRIENT AND PIGMENT SIGNATURES OF MICROBIAL LIFE FROM ARID ENVIRONMENT OF WHITE SANDS NATIONAL MONUMENT, NEW MEXICO

Sulfates are a constitutive part of rocks and regolith exposed to the surface of Mars. The White Sands National Monument (WSNM) (New Mexico) with its gypsum desert is an excellent terrestrial analog to sulfate deposits on Mars and a unique natural laboratory for studying arid evaporitic ecosystems and their relations to microbial life, as well as the potential of such environments for preservation of organics through geologic time. We analyzed gypsum-rich sand, sediments, and crusts with contribution of halite, jarosite and clay collected from the dunes and paleodunes, crusts from the surface of extinct Lake Otero, and jarosite-rich crusts from the surface of dried Lake Lucero. At places 20 cm long selenite crystals formed. Most of the microbial mat was found at the dune field, associated with paleodunes. Available nitrate and ammonium nutrients from the analyzed samples show that nitrogen content from nitrates prevails over nitrogen content from ammonium (2.8:1), showing predominance of oxidizing environments. The reduced environments were found in well-developed cyanobacterial mats. The presence and quantity of available nitrogen depends on the stability and moisture content of the substrate. Chlorophyll-a, chlorophyll-b, bacteriochlorophyll, phycocyanin, bacteriorhodopsin, β-carotene, scytonemin, and carotenoids which overlap in the spectra with photo-protective chlorophyll were present. Based on the spectral characteristics of our samples cyanobacteria, halophilic bacteria and/or archaea, and possibly some other types of archaea and bacteria were found. For example, as most of carotenoid spectra exhibit shoulders at 430 wave numbers, they may belong to brown pigmented bacteria (e.g. Rhodopseudomonas). The identification of prominent scytonemin indicative peaks in most of the spectra point out that microbes have developed protective mechanisms against solar radiation. Additionally, the microbial mats found in the area developed approximately one centimeter under the surface, close to moist areas, which offers an additional UV shield. The desert environments at the WSNM appear to be inhabited by diverse microbial communities well adapted to arid conditions. Constrains on the ecology of microbial communities and their interaction with available minerals will be discussed.