The Functional Significance of Bacterial Predators

Area of Science:

• Microbial Ecology
• Ecosystem Dynamics
• Predator-Prey Interactions

Background:

• Predation shapes ecosystems, influencing food webs and nutrient cycling, effects well-documented for macroscopic predators.
• Predatory bacteria are common in microbial communities, but their growth rates and roles in energy flow are poorly understood due to quantification challenges.

Purpose of the Study:

• To quantify the growth rates and carbon assimilation of predatory bacteria compared to nonpredatory bacteria.
• To assess the impact of added carbon substrates on the growth of different bacterial predator types.
• To elucidate the functional significance of bacterial predators in microbial food webs.

Main Methods:

• Synthesized data from 82 experiments across 15 sites, analyzing over 100,000 taxon-specific measurements.
• Tracked element flow into newly synthesized bacterial DNA using isotopically labeled substrates.
• Compared growth and carbon uptake rates between obligate, facultative, and nonpredatory bacteria.

Main Results:

• Obligate predatory bacteria showed 36% higher growth and 211% higher carbon assimilation than nonpredatory bacteria.
• Facultative predators exhibited lower but still elevated rates (6% growth, 17% assimilation).
• Added carbon substrates disproportionately stimulated obligate predators (63-81% higher responses), indicating trophic control.

Conclusions:

• Predatory bacteria, particularly obligate ones, are highly active and play a significant role in microbial food webs.
• Their functional importance increases with energy flow, influencing element cycling.
• These findings support ecological theory on predator control of lower trophic levels in microbial ecosystems.