The mixotrophic protist Ochromonas danica is an indiscriminant predator whose fitness is influenced by prey type

Abstract

Microbial predator-prey interactions are one of the primary trophic interactions linking biogeochemical cycles to ecosystem dynamics. The mixotrophic flagellate Ochromonas danica was used as a model predator to investigate feeding trends when supplied with actively growing and non-growing bacteria representing a variety of phylogenetic groups. The rate at which bacteria were ingested and the subsequent growth rate (ecological fitness) of O. danica were determined for each type of prey in each growth state. O. danica preferred bacteria between 0.6 and 1.0 µm 3 . It was, in general, an indiscriminate predator in that it readily ingested growing and non-growing bacteria spanning a range of phylogenetic groups, with some notable exceptions. Bacilli/Actinobacteria were ingested at significantly lower rates than Alpha-and Gammaproteobacteria. There were no significant differences among rates at which Proteobacteria (Alpha-, Beta-, and Gamma-) were ingested. The ecological fitness of O. danica could not be predicted from ingestion rates. Predation on Bacilli/Actinobacteria resulted in growth rates significantly lower than when the flagellate preyed upon Gammaproteobacteria. Betaproteobacteria were readily ingested but always resulted in a significant decline in predator fitness. The data reveal that different types of bacteria have different nutritional value to a consumer. If other flagellates respond similarly, then it would seem that trophic transfer efficiency and nutrient regeneration depend on the diet-breadth of predators. KEY WORDS: Bacterivory · Trophic interactions · Predator-preyResale or republication not permitted without written consent of the publisher

Experimental evidence of the quantitative relationship between the prokaryote ingestion rate and the food vacuole content in mixotrophic phytoflagellates

“…). The highest rates were within the range of maximum values reported in the literature when temperature is > 10 °C; for instance, up to 24, 16 and 18 prey protist −1 h −1 in Ochromonas danica (Foster and Chrzanowski, ), Campylomonas marsonii (Izaguirre et al ., ) and Dinobryon sociale (Princiotta et al ., ) respectively. As a reference, if we consider the average C content of a bacterial cell estimated in previous studies (9.15 fg C cell −1 ) (Felip et al ., ), the carbon ingestion rate would be between 0.04 and 5 pg C protist −1 day −1 .…”

Interaction-Specific Changes in the Transcriptome of Polynucleobacter asymbioticus Caused by Varying Protistan Communities

“…lacustris and lowest for the species C. danica with the species P. malhamensis in between - corresponding to the decreasing cell size and the decreasing contribution of phototrophy in the nutrition from C. danica over P. malhamensis to Ps. lacustris (Boenigk et al, 2004, 2006; Schmidtke et al, 2006; Foster and Chrzanowski, 2012; Johnke et al, 2017).…”

“…From grazing experiments with single predator species, it is known that chrysophytes feed on small ultramicrobacteria but prefer larger bacteria (Boenigk et al, 2006; Foster and Chrzanowski, 2012). Predation on Polynucleobacter strains by chrysophytes was investigated in detail and edibility was demonstrated for all investigated strains (Boenigk et al, 2004).…”

Prey element stoichiometry controls ecological fitness of the flagellate Ochromonas danica

“…Bacteria were maintained at RT on R2A agar (Difco). The bacteria used as prey (see Table 1) were existing laboratory strains, obtained from the American Type Culture Collection (ATCC) (www.atcc.org/) or were isolated from freshwater (Foster & Chrzanowski 2012b). The identity of all strains was verified by 16S rRNA gene sequencing.…”

“…Samples were taken 1 h after predator and prey were combined and every 45 min thereafter for a total elapsed time of 3.25 h. Samples were preserved in ice-cold glutaraldehyde (2% final concentration) and stored (4°C) until processed by flow cytometry. A flow cytometer (BD LSRII, 488 nm argon laser) was used to quantify Ochromonas danica and bacteria according to the methods outlined in Foster & Chrzanowski (2012b).…”