How food quality characteristics of bacterial prey modulate growth and community dynamics of bacterivorous flagellates?
Communities of heterotrophic nanoflagellates (HNF, cell sizes from 2-8 µm) represent a considerable part of plankton associations and are the most numerous predators of bacteria. However, different bacterioplankton species represent different food quality resources for HNF communities, potentially affecting flagellate growth, community dynamics and carbon flow to higher trophic levels. However, our knowledge of such dynamics is still very limited.
Karel Šimek and his colleagues from the Biology Centre CAS conducted 11 experiments with natural HNF communities from distinct seasonal phases in two freshwater habitats. The flagellate communities were firstly released from predation pressure of large zooplankton and then incubated with 16 distinct ecologically relevant and abundant prey bacterial strains from different lakes. These bacterial strains belong to important Betaproteobacteria genera (Limnohabitans, Polynucleobacter and Methylopumilus) and one Actinobacteria strain from the Luna 2 cluster.
We observed remarkable prey- and season-specific variability in flagellate community growth parameters, i.e., doubling time, gross growth efficiency, and length of lag phase. All strains, except for the actinobacterium, supported rapid flagellate predator population growth with an average doubling time of 10 hours. Our analysis revealed that large variability in flagellate growth efficiency data was explained by the length of lag phase after prey amendments. This indicates a considerable “adaptation time,” during which the predator communities undergo compositional shifts toward flagellated bacterivore species best adapted to grow on the offered prey. Importantly, the rapid HNF growth detected on various bacteria tightly corresponds to doubling times reported for fast growing bacterioplankton groups. We propose a conceptual model explaining the tight linkages between rapid bacterial community shifts and succeeding flagellate community shifts, which optimize prey utilization rates and carbon flow from various bacteria to the microbial food chain.
Figure: Heterotrophic flagellates – examples of uptake of bacteria from different bacterial phyla. Different bacterial groups were detected directly in food vacuoles of bacterivorous flagellates by means of specific in situ hybridization (FISH) phylogenetic probes.
Šimek K., Grujčić V., Hahn M., Horňák K., Jezberová J., Kasalický V., Nedoma J., Salcher M., Shabarova T. (2018) Bacterial prey food characteristics modulate community growth response of freshwater bacterivorous flagellates Limnology and Oceanography 63: 484–502.