Photoadaptation Alters the Ingestion Rate of Paramecium bursaria, a Mixotrophic Ciliate

Abstract

Bacteriovorous protozoa harboring symbiotic algae are abundant in aquatic ecosystems, yet despite a recent interest in protozoan bacterivory, the influence of light on their ingestion rates has not been investigated. In this study, Paramecium bursaria containing endosymbiotic Chlorella was tested for the effect of light on its ingestion rate. P. bursaria was grown for 4 to 6 days under five different light fluxes ranging from 1 to 90 microeinsteins s -1 m -2 . Ingestion rates were determined by using 0.77-μm-diameter fluorescent microspheres. 4′,6-Diamidino-2-phenylindole dihydrochloride-labeled Enterobacter cloacae was used in one experiment to confirm differences in uptake rates of bacteria by P. bursaria. Unlike phagotrophic phytoflagellates, the ciliates demonstrated different ingestion rates in response to different light intensities. Although symbionts contribute carbon to their host via photosynthesis, the paramecia of the present study fed faster after exposure to higher light intensities, whereas their aposymbiotic counterparts (lacking endosymbionts) were unaffected. Light-induced changes in ingestion rates were not immediate, but corresponded to the period of time required for endosymbiont populations to change significantly. This strongly suggests that the symbionts, stimulated by higher light levels, may dictate the feeding rates of their hosts. Thus, light, apart from temperature, may influence the impact of certain protists on natural bacteria and may affect laboratory-based determinations of protistan feeding rates.

Fending for oneself or partnering up: Competition between mixo- and heterotrophic ciliates under dynamic resource supply

“…In general, ciliates have the potential to reach higher gross growth efficiencies through acquired phototrophy (Stoecker et al 2009, Leles et al 2018), in particular when combined with sufficient food supply. For example, an increased food uptake of the eSNCM P. bursaria during phases of high light intensity has been interpreted as a strategy to increase nutrient supply to the symbionts to meet their demands during phases of increased photosynthetic activity (Berk et al 1991). Similarly, we observed an increase in the relative abundance of C. mixo when prey pulses were associated with either constant light or high light phases, especially when heterotroph abundances were low, while being unaffected or even declining when prey pulses coincided with low-light conditions.…”

“…Endosymbiotic mixotrophs enable the comparison of symbiont-bearing and symbiont-free organisms of the same genus, or even the same species. The symbiont-bearing ciliate P. bursaria, for instance, exhibited lower ingestion rates than symbiont-free populations of the same species (Berk et al 1991, Miura et al 2017, which, however, depended on light intensity, approaching levels similar to those of the heterotrophic P. bursaria at high light (Berk et al 1991). Receiving metabolic benefits from their symbionts has been shown to increase the competitive ability of the eSNCM P. bursaria and to facilitate its coexistence with the heterotroph Colpidium sp.…”

“…Endosymbiotic mixotrophs enable the comparison of symbiont-bearing and symbiont-free organisms of the same genus, or even the same species. The symbiont-bearing ciliate P. bursaria, for instance, exhibited lower ingestion rates than symbiont-free populations of the same species (Berk et al 1991, Miura et al 2017, which, however, depended on light intensity, approaching levels (which was not certified by peer review) is the author/funder. All rights reserved.…”

“…The copyright holder for this preprint this version posted November 6, 2023. ; https://doi.org/10.1101/2023.11.06.564392 doi: bioRxiv preprint similar to those of the heterotrophic P. bursaria at high light (Berk et al 1991). Receiving metabolic benefits from their symbionts has been shown to increase the competitive ability of the eSNCM P. bursaria and to facilitate its coexistence with the heterotroph Colpidium sp.…”

Establishment of an unfed strain of Paramecium bursaria and analysis of associated bacterial communities controlling its proliferation

“…The green P. bursaria is most commonly cultivated in lettuce media containing exogenous microorganisms provided as food ( Barna and Weis, 1973 ; Weis, 1975 ). The type of food varies depending on laboratories and research groups, and a wide variety of microorganisms, such as Klebsiella pneumoniae ( Berk et al, 1991 ; Kosaka, 1991 ; Greczek-Stachura et al, 2021a ) and Chlorogonium elongatum ( Sonneborn, 1970 ; Steinbrück et al, 1981 ; Görtz, 1982 ; Omura et al, 2004 ), are used. However, the ingredients of lettuce leaves differ from region to region ( Barta and Tibbitts, 1991 ; Boroujerdnia and Ansari, 2007 ; Urbonavičiūtė et al, 2007 ; Chang et al, 2014 ), and cultivation conditions are not standardized.…”