Bacterial communities and the nitrogen cycle in the gypsum soils of Cuatro Ciénegas Basin, coahuila: a Mars analogue

Abstract

The OMEGA/Mars Express hyperspectral imager identified gypsum at several sites on Mars in 2005. These minerals constitute a direct record of past aqueous activity and are important with regard to the search of extraterrestrial life. Gale Crater was chosen as Mars Science Laboratory Curiosity's landing site because it is rich in gypsum, as are some desert soils of the Cuatro Ciénegas Basin (CCB) (Chihuahuan Desert, Mexico). The gypsum of the CCB, which is overlain by minimal carbonate deposits, was the product of magmatic activity that occurred under the Tethys Sea. To examine this Mars analogue, we retrieved gypsum-rich soil samples from two contrasting sites with different humidity in the CCB. To characterize the site, we obtained nutrient data and analyzed the genes related to the N cycle (nifH, nirS, and nirK) and the bacterial community composition by using 16S rRNA clone libraries. As expected, the soil content for almost all measured forms of carbon, nitrogen, and phosphorus were higher at the more humid site than at the drier site. What was unexpected is the presence of a rich and divergent community at both sites, with higher taxonomic diversity at the humid site and almost no taxonomic overlap. Our results suggest that the gypsum-rich soils of the CCB host a unique microbial ecosystem that includes novel microbial assemblies.

FIG. 1.

Taxonomic distribution of the 16S rRNA gene sequences obtained from the clone libraries of two studied sites: dry and humid, within the Churince system in the CCB, Mexico. Previously published clone libraries from biological soil crusts (BSCs) and soil: Sonoran Desert BSC (Nagy et al., 2005), Colorado Plateau BSC (Gundlapally and Garcia-Pichel, 2006), McMurdo Dry Valleys soil (Pointing et al., 2009), and Atacama Desert soil (Connon et al., 2007). Relative abundances are shown as percentages of the total number of clones retrieved from each library. Color images available online at www.liebertonline.com/ast

FIG. 2.

Rarefaction curves showing 95% confidence interval for the 16S rRNA gene clone libraries of the two studied sites: dry (DL) and humid (R) within the Churince system in the CCB, Mexico. OTUs were determined at 97% sequence identity.

FIG. 3.

Neighbor-joining tree for the nifH gene OTUs from the two studied sites: dry and humid within the Churince system in the CCB, Mexico. Gray circles indicate nodes with bootstrap support >0.5. Relative abundances are shown as gray bars for the dry site and as black bars for the humid site.

FIG. 4.

Neighbor-joining tree for the nirK gene OTUs from the two studied sites: dry and humid, within the Churince system in the CCB, Mexico. Gray circles indicate nodes with bootstrap support >0.5. Relative abundances are shown as gray bars for the dry site and as black bars for the humid site.

FIG. 5.

Neighbor-joining tree for the nirS gene OTUs from the two studied sites: dry and humid, within the Churince system in the Cuatro Ciénegas Basin, Mexico. Gray circles indicate nodes with bootstrap support >0.5. Relative abundances are shown as gray bars for the dry site and as black bars for humid site.