Biogeography of American Northwest Hot Spring A/B'-Lineage Synechococcus Populations

Area of Science:

• Microbiology
• Ecology
• Genetics

Background:

• Previous studies on hot spring cyanobacteria diversity were limited by low-resolution molecular markers.
• Unicellular cyanobacteria, specifically A/B'-lineage Synechococcus, inhabit island-like hot springs globally.

Purpose of the Study:

• To investigate the structuring of Synechococcus diversity using high-throughput sequencing.
• To determine the relative roles of geographic separation and geochemical differences in shaping cyanobacterial populations.
• To identify endemic lineages and predict ecotypes within hot spring ecosystems.

Main Methods:

• High-throughput sequencing of the psaA gene segment from Synechococcus samples.
• Phylogenetic analyses to identify endemic lineages.
• Ecotype Simulation 2 to predict ecotypes and their membership.
• Canonical correspondence analysis to assess geographic and geochemical influences on ecotype distribution.

Main Results:

• Sequence identity decreased with increasing geographic distance between hot springs.
• Phylogenetic analyses revealed endemic lineages linked to geographic isolation and geochemistry.
• Geographic separation (longitude, latitude) was the primary driver of ecotype distribution across Oregon and Yellowstone.
• Geochemical factors (magnesium, sulfate, sulfide, boron, silicon dioxide, chloride, pH) significantly influenced ecotype distribution, particularly within the Greater Yellowstone Ecosystem.
• Allopatry may play a role in ecotype distribution even at local scales, as indicated by variations in similar chemical environments.

Conclusions:

• Synechococcus populations in hot springs exhibit divergence driven by both physical isolation and environmental geochemistry.
• Geographic distance and local geochemical conditions are key factors structuring cyanobacterial diversity.
• Independent evolution of Synechococcus populations occurs on surprisingly local scales, leading to distinct ecotypes.