Functional tradeoffs underpin salinity-driven divergence in microbial community composition

Area of Science:

• Microbial Ecology
• Environmental Microbiology
• Genomics

Background:

• Bacterial communities in the ocean change subtly across gradients.
• Significant phylogenetic differences exist between freshwater and marine bacteria, but mechanisms are unclear.

Purpose of the Study:

• To investigate if bacterial functional potential explains the divergence between freshwater and marine microbiomes.
• To identify how salinity gradients impact microbial community composition and function.

Main Methods:

• Metagenomic sequencing of microbial communities.
• Analysis along an 1,800 km Baltic Sea salinity gradient (limnic to marine).
• Multivariate statistical analyses to determine key environmental drivers.

Main Results:

• Salinity is the primary driver of changes in microbial community composition and core metabolic functions.
• Distinct metabolic pathways for respiration, biosynthesis, glycolysis, and osmolyte transport were found at high and low salinities.
• Some bacteria, like SAR11, demonstrated adaptability across the entire salinity range.

Conclusions:

• Differences in central metabolism at varying salinities dictate the divide between freshwater and marine microbiomes.
• The ability to inhabit different salinity regimes likely evolved early in bacterial phylogeny.
• Salinity must be considered in climate change models predicting altered precipitation and reduced salinity.