Unveiling plasmid diversity and functionality in pristine groundwater

Area of Science:

• Microbiology
• Genomics
• Environmental Science

Background:

• Plasmids are crucial for genetic diversity but their role in continental subsurface microbial reservoirs is unknown.
• Groundwater represents a significant, yet understudied, microbial reservoir.

Purpose of the Study:

• To analyze the genetic and functional diversity of plasmids in a hillslope aquifer system.
• To evaluate the role of plasmids in horizontal gene transfer (HGT) within this environment.

Main Methods:

• Metagenomic analysis of 32 samples from six groundwater wells.
• Identification and classification of mobile genetic elements (MGEs), focusing on plasmids.
• Functional analysis of plasmid-borne genes and correlation with microbial communities.

Main Results:

• Identified 664 plasmids, showing well-specific populations with limited sharing across sites.
• Plasmids were associated with diverse microbial phyla, including Candidate Phyla Radiation (CPR) bacteria.
• Conjugative plasmids contained genes for metabolism (e.g., cobalamin biosynthesis, hydrocarbon degradation).
• No high-confidence emerging antibiotic resistance genes were detected, unlike in polluted environments.

Conclusions:

• Groundwater plasmids exhibit significant diversity and play a role in microbial community eco-evolution.
• The absence of antibiotic resistance genes underscores the importance of conserving pristine groundwater ecosystems.