Microbial Communities in Atacama Desert

Dessicated and UV Stressed Environments

• Atacama Desert, Chile: one of the driest deserts on Earth, with lithobiontic microbial communities that interact between cyanobacteria and green algae with heterotrophic bacteria, colonizing minerals like dolomite, granite, and gypsum.
• Chroococcidiopsis spp.: a cyanobacterium that is desiccation and radiation tolerant, with survival strategies including the ability to protect and repair DNA damaged by UV, and maintaining proteins and membrane integrity via EPS sheath.
• May help understand life on other planets like Mars.

Hot Environments

• Endolithic community: contains only procaryotes, with photosynthetic primary producers being cyanobacteria, accompanied by small colorless or orange-pigmented non-photosynthetic bacteria.
• Example: limestone rock from Negev desert, Israel.

Aphotice Environments Based on Chemolithoautotrophy

• Deep Sea Hydrothermal Vents: magma-derived hydrothermal convection causes hot water laced with minerals to flow up through cracks and fissures, resulting in anoxic, acidic conditions enriched in CO2, H2S, CH4, H2, Fe2+, Zn2+, and Cu2+.
• Microbial communities develop based on chemoautotrophy, e.g. methanotrophic microbes.
• Black smoker vent: chemolithotrophic sulfur-oxidizing bacteria associated with the trophosome tissue of tube worms.
• Entire food web in a hydrothermal vent community is based on chemoautotrophy, not photoautotrophy.

Extreme Environments

• "Extreme" based on temperature, moisture, pH, salinity, contaminants, etc.

Low Temperature Environments

• McMurdo Dry Valleys, Antarctica: driest and coldest ecosystem on Earth, with sulfide gradients in Lake Fryxell resulting in microbial sulfur cycling.
• Cold adapted microbes synthesize cold adapted enzymes, which have higher activity at low temperatures, used in biotechnology.

Endolithic Microorganisms

• Colonization is dependent on physical properties of the rock, such as color, opacity, and porosity or presence of fissures.
• Rock with low specific gravity does not support endolithic growth.
• Morphology of endolithic colonization in cold and hot deserts is remarkably similar, with an uppermost 1 to 3 mm of the rock being free from microorganisms.

Aphotice Environments Based on Chemolithoautotrophy

• Acid Mine Drainage: mining of pyrite (FeS2) deposits results in S2- oxidized to SO42+ + H+, lowering pH and mobilizing metals.
• Specialized microbial communities develop based on chemoautotrophy.
• Metagenomic analysis: sequences were reconstructed to give nearly complete genomes for two iron-oxidizing bacteria, Leptospirillum group II and Ferroplasma type II.
• Fluorescent in situ hybridization analysis: Leptospirillum group II is dominant (75%) with Ferroplasma type II representing approximately 10% of the community.

Aphotice Environments Based on Chemolithoautotrophy

• Desert Carbonate Cave: devoid of phototrophic primary production, receiving fixed organic carbon from drip water that forms speleotherms.
• Kartchner Caverns: unexpectedly high bacterial diversity, with ≃ 2000 operational taxonomic units, dominated by heterotrophic growth, and 10% of metagenome comprised of archael sequences.
• One gene category that was significantly overrepresented in the cave metagenomes was DNA repair enzyme genes belonging to the RAMP (Repair Associated Mysterious Proteins) superfamily.