Microbial Interactions and Grazing Dynamics in Aquatic Ecosystems

Aquatic microbial communities form the foundation of biogeochemical cycling and food-web dynamics in lakes, rivers and oceans. Photosynthetic microbes such as phytoplankton fix inorganic carbon and release oxygen, while heterotrophic bacteria decompose organic matter and regenerate nutrients. Protists—including ciliates and nanoflagellates—exert top-down control through selective grazing, shaping bacterial diversity, functional traits and nutrient fluxes. Interactions range from mutualistic exchanges of vitamins and metabolites to antagonistic dynamics in which grazing pressure selects for defence strategies. These microbial interactions govern carbon flow via the microbial loop, influence stoichiometric balances and mediate ecosystem resilience to perturbations such as eutrophication or climate-driven shifts in temperature and stratification. Recent advances have elucidated chemotactic responses to resource gradients, inducible defence mechanisms, diel shifts in grazing selectivity and mechanistic underpinnings of prey capture, providing a more integrated picture of how microscale processes scale up to influence global biogeochemical cycles and water-quality management.

Research from Nature Portfolio

Recent studies have shown that nutrient availability and predation pressure jointly drive the selection of protozoa-resisting bacteria in freshwater microcosms. Under high predation pressure, genera such as Mycobacterium increase in abundance, reflecting evolved resistance strategies. Conversely, disturbances favour opportunistic taxa like Pseudomonas, highlighting how perturbations reshape food-web interactions. This work combines joint species distribution models with microbial community profiling to reveal how bottom-up and top-down forces interact to structure bacterial assemblages and influence ecosystem function.

Microbial Interactions and Grazing Dynamics in Aquatic Ecosystems publication trend

The graph below shows the total number of articles in microbial interactions and grazing dynamics in aquatic ecosystems across all publications each year (not limited to Nature Index journals).

Technical terms

Microbial loop: The recycling pathway in which dissolved organic matter is taken up by bacteria, transferred to protists and re-incorporated into the classical food web.

Heterotrophic nanoflagellate: A small, flagellated protist that consumes bacteria and picophytoplankton, playing a key role in microbial predation.

Grazing resistance: Strategies adopted by bacteria—such as aggregation or inducible defences—that reduce susceptibility to protist predation.

Functional response: The relationship between prey density and the rate at which a predator ingests prey, shaped by feeding currents and handling time.

Stoichiometry: The elemental ratio (e.g., carbon:nitrogen:phosphorus) in organisms that influences growth, nutritional quality and predator-prey interactions.

References

1. Predators and nutrient availability favor protozoa-resisting bacteria in aquatic systems. Scientific Reports (2018).
2. Protistal Grazers Increase Grazing on Unicellular Cyanobacteria Diazotroph at Night. Frontiers in Marine Science (2020).
3. Mechanisms and fluid dynamics of foraging in heterotrophic nanoflagellates. Limnology and Oceanography (2022).
4. Grazing resistance developed in Escherichia coli K-12 during coexistence with a bacterivorous protist. PLOS ONE (2024).