Aqueous Geochemical Controls on the Sestonic Microbial Community in Lakes Michigan and Superior

Area of Science:

• Microbial Ecology
• Limnology
• Great Lakes Ecosystems

Background:

• The Laurentian Great Lakes, the world's largest freshwater system, have poorly understood sestonic microbial communities.
• Understanding microbial structure is crucial for assessing the health and functioning of these vital freshwater ecosystems.

Purpose of the Study:

• To investigate the microbial community structure in Lakes Superior and Michigan as a function of water depth.
• To identify key environmental drivers influencing microbial composition in the Great Lakes.

Main Methods:

• High-throughput sequencing of microbial communities.
• Analysis of physicochemical parameters (temperature, dissolved oxygen, pH, nutrients) across water depths.
• Statistical analysis to correlate microbial abundances with environmental variables.

Main Results:

• Significant differences in microbial phyla (Actinobacteria, Bacteroidetes, Cyanobacteria, Thaumarchaeota, Verrucomicrobia) were found between lakes.
• Phosphorus limitation was indicated by high N:P ratios (97:1).
• Dissolved oxygen, pH, temperature, and salinity were identified as major drivers of microbial community structure.

Conclusions:

• Microbial community composition in the Great Lakes is significantly influenced by water depth and associated physicochemical gradients.
• Ammonia-oxidating archaea, specifically *Candidatus Nitrosopumilus*, play a notable role in nitrogen cycling in Lake Superior.
• Environmental factors like dissolved oxygen, pH, temperature, and salinity are critical in shaping the microbial landscape of the Great Lakes.