Effects of Bacillus cereus Endospores on Free-Living Protist Growth
We studied the predator–prey interactions between heterotrophic protists and endospores of Bacillus cereus group bacteria, in order to gain insight on survival and dispersal of B. cereus endospores in the environment. It has been hypothesised that the spore stage protects against digestion by predating protists. Therefore, experiments were carried out to investigate the impact of B. cereus endospores and vegetative cells, as the only food source, on individual amoeboid, flagellated and ciliated protists. The presence of fluorescent-labelled intracellular bacteria confirmed that B. cereus endospores as well as vegetative cells were ingested by protists and appeared intact in the food vacuoles when observed by epifluorescence microscopy. Furthermore, protist growth and bacterial predation were followed by qPCR. Protists were able to grow on vegetative cells as well as endospores of B. cereus, despite the lower cell division rates observed for some protists when feeding on bacterial endospores. Survival and proliferation of ingested bacteria inside protists cells was also observed. Finally, B. cereus spore germination and growth was observed within all protists with higher abundance in the amoeboid protist after antibiotic treatment of the protist surface. These observations support that protists can act as a potential breeding ground for B. cereus endospores.
KeywordsBacterivorous protist Food quality Growth rates Ingestion rates Predator–prey interaction Soil food web
This research is part of the European project Trainbiodiverse and was funded by Marie Curie Actions. Authors would like to thank Inês Nunes for all the help and support during the RNA work and Tina Thane, Tanja Begovic and Pia Petersen for laboratory support.
Compliance with Ethical Standards
This work was supported by the European Union’s Seventh Framework Programme for research, technological development and demonstration under grant agreement no. (289949) and the eDNA center supported by the Danish Centre for Environment and Energy at Aarhus University. HHJ received support from the VELUX foundation to procure microscopes and tools from epi-fluorescence microscopy grant no. (VKR022608).
Conflict of Interest
- 9.Amaro F, Wang W, Gilbert JA, et al. (2015) Diverse protist grazers select for virulence-related traits in Legionella. ISME J 1–12Google Scholar
- 17.Page FC (1988) A new key to freshwater and soil gymnamoebae with instruction for culture. Freshw. Biol. AssocGoogle Scholar
- 29.Motulsky HJ, Christopoulos A (2003) Fitting models to biological data using linear and nonlinear regression. GraphPad Software, Inc, San Diego 351 ppGoogle Scholar
- 33.Fowler J, Cohen L, Jarvis P (1998) Practical statistics for field biology. Wiley, ChichesterGoogle Scholar
- 39.Weber AAT, Pawlowski J (2013) Can abundance of protists be inferred from sequence data: a aase study of foraminifera. PLoS One 8:1–8Google Scholar