# Diversity and varying predation capacities of culturable Amoebozoae against opportunistic vibrios in contrasting Mediterranean coastal environments

## TL;DR

This study explores how different types of free-living amoebae interact with bacteria in Mediterranean coastal waters, revealing their habitat preferences and varying abilities to control bacterial populations.

## Contribution

The study reveals distinct habitat preferences and predation capacities of Amoebozoa in marine environments, emphasizing the need for taxonomically detailed investigations.

## Key findings

- Vannellidae were enriched in water, while Paramoebidae were enriched in sediments.
- Vibrio tasmaniensis inhibited Vannellidae growth, while Vibrio crassostreae inhibited Paramoebidae growth.
- Amoebozoa diversity and predation capacities vary across different coastal environments.

## Abstract

Free-living amoebae (FLA) are ubiquitous and can be found in many environments including soil, freshwater, and marine environments. They feed on various microorganisms and can play an important role in the food web and its dynamics. We previously described that FLA belonging to the Vannella genus isolated from oyster farms in the Thau lagoon in France are able to establish stable interactions with Vibrionaceae, suggesting they can play a role in pathogen dynamics. To further investigate the ecological interactions between FLA and Vibrionaceae in Mediterranean coastal waters, we conducted monthly sampling for 1 year at three contrasting sites. FLA populations were isolated from water and sediment samples on different bacterial lawns, including Escherichia coli or Vibrio tasmaniensis, Vibrio crassostreae, and Vibrio harveyi. Diversity analysis by v4-18S barcoding revealed distinct communities between fractions and sites. The Vannellidae were found significantly enriched in the water, whereas Paramoebidae were found enriched in the sediments. Additionally, uneven distribution of Vexilliferidae, Vermistellae, and, to a lesser extent, Acanthamoebidae and Subulatomonas contrasted between sampling sites. Selection of grazers on different bacterial lawns revealed that V. tasmaniensis inhibits the growth of most Vannellidae, whereas V. crassostreae inhibits the growth of Paramoebidae. These differences were further confirmed functionally using isolates belonging to each Amoebozoa taxonomic group. Overall, our results highlight the need for more comprehensive studies of the diversity and population dynamics of Amoebozoa in marine environments and indicate that the role of these diversified grazers in shaping Vibrio communities is complex and still poorly characterized.

Although they can play an important role in shaping bacterial communities and as intracellular niches for potential pathogens, the diversity and ecology of free-living amoebae (FLA) in marine environments are still poorly characterized. Very few studies have used systematic approaches to unravel the population dynamics and ecological variations of FLA in different environments. Our study in marine coastal environments highlights that FLA taxonomic groups can harbor habitat preferences and have different predation capacities, suggesting that FLA-bacteria interactions need to be considered at different taxonomic levels to uncover generalist versus specialist adaptations.