Streamlined and Abundant Bacterioplankton Thrive in Functional Cohorts

Area of Science:

• Microbial Ecology
• Freshwater Microbial Communities
• Bacterioplankton Dynamics

Background:

• Fastidious microbes are abundant but difficult to culture due to dependencies.
• Microbial cooperation, including kin and community interactions, is crucial for their survival and dominance in natural environments.
• Understanding these metabolic partnerships is key to explaining microbial ubiquity and abundance.

Purpose of the Study:

• To investigate cooperation models explaining the abundance and ubiquity of dominant bacterioplankton genera in a freshwater lake.
• To identify the primary cohorts and metabolic partners for "Candidatus Planktophila" (acI-A), "Candidatus Nanopelagicus" (acI-B), and "Candidatus Fonsibacter" (LD12).
• To examine the role of specific cooperative mechanisms, such as the enzyme KatG, in microbial survival.

Main Methods:

• Employed culture-dependent methods (dilution mixed cultures).
• Utilized culture-independent methods, including small subunit (SSU) rRNA gene time series and environmental metagenomics.
• Independently identified key bacterial genera and their potential cooperative partners.

Main Results:

• Identified "Ca. Planktophila" (acI-A), "Ca. Nanopelagicus" (acI-B), and "Ca. Fonsibacter" (LD12) as dominant fastidious bacterioplankton.
• Found that "Ca. Planktophila" and "Ca. Fonsibacter" have potential for laboratory complementarity despite no natural correlation.
• Demonstrated that ecotype and community cooperation explain "Ca. Planktophila" abundance, while "Ca. Nanopelagicus" and "Ca. Fonsibacter" success is better explained as a community by-product.

Conclusions:

• Cooperation strategies, including by-product benefits and shared resources like KatG, are essential for the coexistence and abundance of dominant freshwater bacterioplankton.
• Different genera employ distinct cooperation strategies, highlighting the complexity of microbial community assembly.
• This study provides a framework for understanding microbial population functioning within complex communities and their impact on global nutrient cycling.