Investigation of prey ingestion and digestion in the ciliate predator
      Tetrahymena pyriformis and the impact on growth
Creators: name: Wong, Oliver
Publisher: name: Lancaster University
Year: 2017

description: This study evaluated the effect of four prey states on ingestion,
      digestive vacuole (DV) formation, digestion and growth in the ciliate
      Tetrahymena pyriformis. The prey included several strains of live
      RFP-expressing heterotrophic bacteria (Live), heat-killed-DTAF-stained
      heterotrophic bacteria (Dead), live autotrophic Synechococcus species
      (Pico) together with fluorescently-labelled microspheres (FLMs). Prey
      biovolume did not affect ingestion rates over the 5 minute period tested,
      therefore the effect of the different prey states could be directly
      compared. Live heterotrophic bacteria were able to quickly upregulate DV
      formation rate; something not demonstrated by any other prey. All prey,
      except FLMs, showed controlled vacuole filling over a 20 minute period
      whereby new DVs contained an equivalent number of prey to those in older
      vacuoles. Live heterotrophic and autotrophic prey yielded a significantly
      lower maximum number of prey/vacuole compared to Dead cells, and whereas
      significant differences in prey/vacuole between bacterial species were
      discerned for Dead species, no such differences were evident for Live
      species. It was hypothesised that ingestion of prey is receptor-mediated
      and that the predominant pathway into the ciliate for Live prey is the
      lectin-receptor-based route, and that for inert prey is the
      non-specific-receptor-mediated route, with a yet unidentified route for
      Dead prey.
      
      Using pulse-chase experiments, the digestion of Live and Dead
      heterotrophic bacteria were found to be equivalent, i.e. ca. 50% of
      ingested cells within a DV were digested. There was however a very strong
      relationship (for both prey states) between biovolume of prey in the
      vacuole and the total biovolume of prey digested in that vacuole implying
      that larger prey cells might lead to higher ciliate specific growth rates.
      This was not found to be the case. No relationship between ciliate
      specific growth rate was discerned with prey biovolume, or even digestion
      rates, as % prey/vacuole/min over the digestion period (where there is a
      linear decline in prey due to digestion). The digestion period (DP) was
      considerably shorted with Dead cells and it was hypothesised that, due to
      an incomplete suite of ligands, DVs did not go through the complete
      sequence of fusion events with lysosomes.
      
      Digestion of prey had little effect on ciliate growth rates. However there
      was no obvious relationship between growth rate and any parameter tested.
      This suggests that digestion and growth are too far removed with regards
      to cellular processes.
      
      In conclusion, the findings suggest that there are two prey recognition
      systems in T. pyriformis, one which recognised prey particles and leads to
      ingestion, and a second, present in the DV, which recognises the type of
      prey enclosed within it and leads to digestion behavioural changes.