Protistan predation interferes with bacterial long-term adaptation to substrate restriction by selecting for defence...

Area of Science:

• Microbial Ecology
• Evolutionary Biology
• Aquatic Microbiology

Background:

• Aquatic bacteria face a trade-off between growth in low-nutrient environments and defense against protistan grazing.
• Bacterial survival strategies include enhanced growth or forming aggregates for protection, but these traits can be mutually exclusive.

Purpose of the Study:

• To investigate the evolutionary response of freshwater bacteria (Sphingobium sp. strain Z007) to distinct selective pressures: low substrate availability and protistan predation.
• To determine if nutrient limitation or predation pressure drives the evolution of bacterial growth performance versus defense mechanisms.

Main Methods:

• An evolutionary experiment was conducted over 26 weeks using Sphingobium sp. strain Z007.
• Cultures were maintained under two conditions: with flagellate predators (P+) and without predators (P-).
• Evolved bacterial phenotypes were analyzed for aggregate formation, growth yield, and metabolic versatility.

Main Results:

• Bacteria evolved distinct phenotypes under predation (P+) versus nutrient limitation (P-).
• P- strains showed increased growth yield and metabolic versatility but reduced aggregation.
• P+ strains exhibited higher aggregation (defense) but lower growth yield and metabolic versatility, losing phenotypic plasticity.

Conclusions:

• Transient exposure to oligotrophic conditions can favor facultative oligotrophic lifestyles in bacteria, aiding aquatic survival.
• Investment in anti-predation defense can limit bacterial adaptation to abiotic environmental changes.
• Evolutionary pressures in aquatic habitats shape bacterial strategies, balancing growth and survival needs.