Microbial Phototrophic, Heterotrophic, and Diazotrophic Activities Associated with Aggregates in the Permanent Ice Cover of Lake Bonney, Antarctica

Area of Science:

• Astrobiology
• Microbial Ecology
• Limnology

Background:

• McMurdo Dry Valley lakes are extreme ecosystems with liquid water.
• Lake Bonney's ice cover harbors microbial habitats formed by soil particles.
• Soil particles heat up, melt into ice, forming aggregates with liquid water.

Purpose of the Study:

• Investigate microbial communities in Antarctic lake ice aggregates.
• Determine the metabolic activities (photosynthesis, N2 fixation) within these aggregates.
• Understand nutrient cycling and microbial self-sustenance in extreme environments.

Main Methods:

• Microautoradiography and physiological studies.
• Analysis of microbial community structure and function.
• Measurement of CO2 and N2 fixation rates in ice and water phases.

Main Results:

• Microbial aggregates contain diverse cyanobacterial-bacterial communities.
• Photosynthesis (CO2 fixation) and N2 fixation occur in liquid water, not ice.
• CO2 fixation by cyanobacteria, N2 fixation by cyanobacteria and eubacteria.
• Nutrient enrichment (NO3-, PO43-, Fe) stimulates fixation rates.
• Microbes modify their environment, creating nutrient-rich oases.

Conclusions:

• Microbial communities in Lake Bonney aggregates are metabolically diverse and self-sustaining.
• These organisms drive biogeochemical cycles in an extreme, nutrient-limited environment.
• The study highlights microbial adaptation and survival strategies in Earth's harsh ecosystems.