Differing Escape Responses of the Marine Bacterium Marinobacter adhaerens in the Presence of Planktonic vs. Surface-Associated Protist Grazers

Abstract

Protist grazing pressure plays a major role in controlling aquatic bacterial populations, affecting energy flow through the microbial loop and biogeochemical cycles. Predator-escape mechanisms might play a crucial role in energy flow through the microbial loop, but are yet understudied. For example, some bacteria can use planktonic as well as surface-associated habitats, providing a potential escape mechanism to habitat-specific grazers. We investigated the escape response of the marine bacterium Marinobacter adhaerens in the presence of either planktonic (nanoflagellate: Cafeteria roenbergensis) or surface-associated (amoeba: Vannella anglica) protist predators, following population dynamics over time. In the presence of V. anglica, M. adhaerens cell density increased in the water, but decreased on solid surfaces, indicating an escape response towards the planktonic habitat. In contrast, the planktonic predator C. roenbergensis induced bacterial escape to the surface habitat. While C. roenbergensis cell numbers dropped substantially after a sharp initial increase, V. anglica exhibited a slow, but constant growth throughout the entire experiment. In the presence of C. roenbergensis, M. adhaerens rapidly formed cell clumps in the water habitat, which likely prevented consumption of the planktonic M. adhaerens by the flagellate, resulting in a strong decline in the predator population. Our results indicate an active escape of M. adhaerens via phenotypic plasticity (i.e., behavioral and morphological changes) against predator ingestion. This study highlights the potentially important role of behavioral escape mechanisms for community composition and energy flow in pelagic environments, especially with globally rising particle loads in aquatic systems through human activities and extreme weather events.

Patterns of bacterial generalists and specialists in lakes and reservoirs along a latitudinal gradient

“…Although biogeographical patterns are crucial for understanding ecology, the distinction between generalists or specialists is often neglected (Villalba et al, 2022) when trying to predict and explain spatial distribution patterns of microbial biodiversity (Xu, Vandenkoornhuyse, et al, 2022). In our study, bacterial diversity and community similarity exhibited variations in generalists and specialists with increasing latitude (Figures 3a,b and S5).…”

Bacteria Release from Microplastics into New Aquatic Environments

“…Furthermore, we consider that free-living bacteria were not under grazing pressure, although we did not check if eukaryotic predators were released from the plastisphere. The particle-attached lifestyle offers many advantages, such as protection from predators, environmental pressures, and antibiotics and access to resources [26], but different top-down (e.g., predation) or bottomup (e.g., the leaching of organic matter and nutrients from surfaces) factors can trigger a habitat shift and bacterial movement into the water [27].…”

Overview of the Molecular Mechanism of Bacterial Environmental Adaptation by Comprehensive Analysis

“…This is because virulence factors are not always expressed in microorganisms but are expressed in adaptation to a certain environment or a certain cellular condition [5][6][7]. Microorganisms are also often used to produce useful compounds, but metabolic pathways do not always maintain the same activity; they change their activities in response to changing environments or cellular conditions [8][9][10]. In short, organisms are often studied for specific functions for specific purposes but understanding them not only from the analysis of specific factors related to those purposes but also in terms of their roles for the organism, their cooperative relationships with cells, and their regulatory network mechanisms, will provide essential understanding and applications.…”

“…The escape behavior might thereby be triggered by the recognition of protist predators via chemical cues. Villalba et al investigated the escape response of the marine bacterium Marinobacter adhaerens in the presence of either planktonic (nanoflagellate) or surface-associated (amoeba) protist predators, following population dynamics [10]. They demonstrated the presence of contrasting defensive mechanisms in the chemotaxis mutant M. adhaerens towards planktonic or surface-attached predators in the two main pelagic habitats: water and particle surfaces.…”