Marine Bacteria Display Different Escape Mechanisms When Facing Their Protozoan Predators

Area of Science:

• Microbiology
• Ecology
• Protistology

Background:

• Free-living amoebae (FLA) are ubiquitous microbial predators in diverse ecosystems, including marine biofilms.
• The interactions between protozoa and marine bacteria are not well understood, particularly bacterial survival strategies against amoebic predation.
• Amoebae like Acanthamoeba castellanii are known bacterial predators, but mechanisms for bacterial evasion remain largely uncharacterized.

Purpose of the Study:

• To investigate the interaction between the ubiquitous amoeba Acanthamoeba castellanii and four marine bacteria.
• To determine if marine bacteria are preyed upon by A. castellanii or if they possess survival mechanisms.
• To elucidate bacterial strategies for surviving predation at both cellular and population (biofilm) levels.

Main Methods:

• Co-culture experiments with axenized Acanthamoeba castellanii and four marine bacterial strains at varying bacteria-to-amoeba ratios.
• Microscopic analysis to track intracellular bacterial fate and localization within amoebae.
• Biofilm formation assays in the presence of A. castellanii or its supernatant to assess population-level responses.

Main Results:

• At low ratios, bacteria were phagocytized but followed distinct intracellular pathways, delaying or preventing digestion.
• Specific bacterial strains exhibited unique intracellular fates, including localization in the amoeba's nucleolus or expulsion in vesicles.
• At higher ratios, biofilms (mono- and multi-species) subjected to A. castellanii showed detachment from surfaces.

Conclusions:

• Marine bacteria display varied and sophisticated escape mechanisms against predation by Acanthamoeba castellanii.
• Bacterial survival strategies operate at both the individual cell level (intracellular evasion) and the community level (biofilm detachment).
• This study provides novel insights into the complex predator-prey dynamics and bacterial resilience within marine microbial communities.