Small freshwater ecosystems with dissimilar microbial communities exhibit similar temporal patterns

Area of Science:

• Environmental microbiology
• Freshwater ecology
• Microbial community dynamics

Background:

• Small freshwater ecosystems are vital biodiversity reservoirs and greenhouse gas contributors, yet their microbial communities are understudied.
• Microorganisms are crucial for biogeochemical cycling and water quality, with small ecosystems being sensitive to environmental changes.
• Understanding spatial and temporal variations in archaeal, bacterial, and microbial eukaryote communities is essential.

Purpose of the Study:

• To investigate the composition and temporal dynamics of microbial communities (archaea, bacteria, microbial eukaryotes) in small freshwater ecosystems.
• To determine how microbial community structure varies across different spatial scales and over seasonal and interannual timeframes.
• To identify the drivers of microbial community assembly, including environmental conditions and biotic interactions.

Main Methods:

• 16S rRNA gene amplicon sequencing was used to monitor archaeal and bacterial community composition over 24 months in four ponds and one brook.
• Microbial eukaryote data from previous investigations in the same systems were integrated.
• Community composition was analyzed in relation to spatial (ecosystem) and temporal (seasonal, interannual) variations.

Main Results:

• Microbial communities were largely unique to each ecosystem, with less than 1% of operational taxonomic units (OTUs) shared among the five sites, indicating strong local environmental influence.
• Candidate Phyla Radiation (CPR) bacteria were unexpectedly diverse and abundant in these oxic environments.
• Marked and consistent seasonal patterns were observed across archaea, bacteria, and microbial eukaryotes, despite significant turnover in rare OTUs.

Conclusions:

• Microbial community structure in small freshwater ecosystems is primarily shaped by environmental conditions and seasonal cycles.
• The high degree of spatial uniqueness suggests strong local selection pressures on microbial communities.
• Biotic associations appear to play a significant role in interannual microbial community assembly, even with stable environmental parameters.