Confusing selective feeding with differential digestion in bacterivorous nanoflagellates

Area of Science:

• Protistology
• Microbiology
• Aquatic Ecology

Background:

• Heterotrophic nanoflagellates are crucial consumers of bacteria in aquatic ecosystems.
• Understanding their food selection mechanisms is vital for aquatic food web dynamics.
• Previous studies using inert particles as bacterial surrogates showed inconsistencies.

Purpose of the Study:

• To analyze food selectivity and selection mechanisms in three species of heterotrophic nanoflagellates: Spumella, Ochromonas, and Cafeteria.
• To investigate the fate of individual prey particles (live bacteria and inert beads) during flagellate interactions.
• To elucidate the role of selective digestion in particle processing.

Main Methods:

• Video microscopy was employed to observe particle-flagellate interactions.
• Experiments involved offering live bacteria and inert beads simultaneously to flagellates.
• Key stages recorded included capture, ingestion, digestion, and egestion.
• Vacuole passage time was measured for different flagellate states (starved vs. exponential phase).

Main Results:

• Flagellates ingested beads and bacteria unselectively when offered together.
• Spumella and Ochromonas egested inert beads rapidly (2-3 min vacuole passage time).
• Starved flagellates showed longer vacuole passage times than exponential-phase ones.
• Cafeteria stored all ingested particles for over 30 minutes, indicating different processing.

Conclusions:

• Selective digestion is a primary mechanism for differential prey particle processing in nanoflagellates.
• Species-specific differences in food selection and digestion were observed.
• This selective digestion mechanism explains discrepancies in studies using inert particles as bacterial surrogates.