Rarity in aquatic microbes: placing protists on the map

Area of Science:

• Microbial Ecology
• Genomics
• Biogeography

Background:

• Most microbial communities are dominated by rare taxa, collectively termed the "rare biosphere".
• High-throughput sequencing (HTS) enables the study of these rare microbial populations.
• Understanding the rare biosphere is crucial for microbial ecology and evolution.

Purpose of the Study:

• To review existing literature on the rare biosphere, with a focus on unicellular eukaryotes (protists).
• To synthesize current knowledge on the ecological roles and characteristics of rare microbial taxa.
• To highlight knowledge gaps and suggest future research directions.

Main Methods:

• Literature review of studies utilizing high-throughput sequencing (HTS).
• Analysis of data pertaining to microbial community structure, biogeography, and phylogenetic diversity.
• Synthesis of evidence regarding the activity and ecological roles of rare taxa.

Main Results:

• The rare biosphere contains both dormant and active microbes with potential key ecosystem roles.
• Rare microbes exhibit biogeographic patterns, sometimes mirroring those of abundant taxa.
• The rare biosphere may harbor phylogenetically deep-branching diversity and act as a functional redundancy reservoir.

Conclusions:

• The rare biosphere is a critical component of microbial communities, influencing ecosystem stability and function.
• Rare taxa may serve as a reservoir for novel functions and deep evolutionary lineages.
• Further research on the rare biosphere is essential for advancing microbial ecology and understanding ecosystem dynamics.