Killing the killer: predation between protists and predatory bacteria

Abstract

Predation by microbes is one of the main drivers of bacterial mortality in the environment. In most ecosystems multiple micropredators compete at least partially for the same bacterial resource. Predatory interactions between these micropredators might lead to shifts within microbial communities. Integrating these interactions is therefore crucial for the understanding of ecosystem functioning. In this study, we investigated the predation between two groups of micropredators, i.e. phagotrophic protists and Bdellovibrio and like organisms (BALOs). BALOs are obligate predators of Gram-negative bacteria. We hypothesised that protists can prey upon BALOs despite the small size and high swimming speed of the latter, which makes them potentially hard to capture. Predation experiments including three protists, i.e. one filter feeder and two interception feeder, showed that BALOs are a relevant prey for these protists. The growth rate on BALOs differed for the respective protists. The filter feeding ciliate was growing equally well on the BALOs and on Escherichia coli, whereas the two flagellate species grew less well on the BALOs compared to E. coli. However, BALOs might not be a favourable food source in resource-rich environments as they are not enabling all protists to grow as much as on bacteria of bigger volume.

A Generalist Protist Predator Enables Coexistence in Multitrophic Predator-Prey Systems Containing a Phage and the Bacterial Predator Bdellovibrio

“…BALO and phage growth, however, significantly decreased in the presence of the protist (Figures 3d,e) and also in the case of BALO when both protist and phage were present (Figure 3b). This indicates that the protist either ingested free BALOs (Johnke et al, 2017), phages (Deng et al, 2014), or BALO-or phage-infected prey, or was the strongest resource competitor. Another possibility is an indirect effect of the overall prey density reduction by protist predation, which might have substantially lowered the resource availability for the BALO and phage and consequently reduced the growth of the latter.…”

“…We hypothesized that the potential trophic complementarity of predators would result in a reduction of all prey species. We further expected direct interactions between the predator species since protists are able to graze directly upon phages (Gonzalez and Suttle, 1993;Hennemuth et al, 2008) and BALOs (Johnke et al, 2017). Finally, the high grazing pressure exerted by specialist predators should induce the emergence of predationresistant bacteria.…”

“…Direct (straight) and indirect (dashed) interactions exist between all predators. Direct predatory interactions are known for protists and BALOs (Johnke et al, 2017); and protists and phages (Deng et al, 2014). Additionally, superinfection of a prey bacterium by a BALO and a phage was shown by 1992) prior to the experiments.…”

Multifaceted aspects of synchrony between freshwater prokaryotes and protists

“…Unexplained variability and variability solely related to temporal variables could be linked to parameters that were not considered, including within‐site environmental gradients, especially strong in B4 and A20, and biotic interactions. The microbial loop concept (Azam et al, ) describes how bacteria and protists interact in manifold ways such as predation (Johnke, Boenigk, Harms, & Chatzinotas, ), competition or mutualism (Seymour et al, ).…”

Prospects for Integrating Disturbances, Biodiversity and Ecosystem Functioning Using Microbial Systems

“…By contrast, specific disturbance responses of different community members may lead to non-random extinctions and are at least as realistic in nature (Srivastava and Vellend, 2005). One option to achieve this is to expose microbes to toxic compounds or resource scarcity for a certain period of time, for instance by cultivating them in miniature membrane bioreactors from which compounds can be washed out or in dialysis bags alternately placed in tanks with or without the compounds (Langenheder et al, 2012;Johnke et al, 2017;Karakoç et al, 2018). Additionally, temperature variation (Jurburg et al, 2017), UV light application (Gibbons et al, 2016) or sonication (Violle et al, 2010) can induce discrete impacts on microbial communities.…”