Feeding currents facilitate a mixotrophic way of life

Abstract

Mixotrophy is common, if not dominant, among eukaryotic flagellates, and these organisms have to both acquire inorganic nutrients and capture particulate food. Diffusion limitation favors small cell size for nutrient acquisition, whereas large cell size facilitates prey interception because of viscosity, and hence intermediately sized mixotrophic dinoflagellates are simultaneously constrained by diffusion and viscosity. Advection may help relax both constraints. We use high-speed video microscopy to describe prey interception and capture, and micro particle image velocimetry (micro-PIV) to quantify the flow fields produced by free-swimming dinoflagellates. We provide the first complete flow fields of free-swimming interception feeders, and demonstrate the use of feeding currents. These are directed toward the prey capture area, the position varying between the seven dinoflagellate species studied, and we argue that this efficiently allows the grazer to approach small-sized prey despite viscosity. Measured flow fields predict the magnitude of observed clearance rates. The fluid deformation created by swimming dinoflagellates may be detected by evasive prey, but the magnitude of flow deformation in the feeding current varies widely between species and depends on the position of the transverse flagellum. We also use the near-cell flow fields to calculate nutrient transport to swimming cells and find that feeding currents may enhance nutrient uptake by E75% compared with that by diffusion alone. We argue that all phagotrophic microorganisms must have developed adaptations to counter viscosity in order to allow prey interception, and conclude that the flow fields created by the beating flagella in dinoflagellates are key to the success of these mixotrophic organisms.

Toxigenic Dinoflagellates and Associated Toxins in San Jorge Gulf, Argentina

“…The association of A. catenella with high inorganic nitrogen concentrations might be related to its trophic strategy, as unlike other mixotrophic species of the genus, this species is autotrophic (Blossom et al, 2012). The other two main species observed in this study (D. acuminata and P. reticulatum) have the capacity to feed on microalgae or bacteria (Reguera et al, 2012;Nielsen and Kiørboe, 2015), which might give them some advantage in low nitrate environments. Moreover, it was established that A. catenella is not a good competitor for nitrate at low concentrations (Collos et al, 2004), so other species might be favored under such circumstances.…”

Effect of TDA‐producing Phaeobacter inhibens on the fish pathogen Vibrio anguillarum in non‐axenic algae and copepod systems

“…The non‐axenic R. salina K‐1487 originates from Denmark and was provided by Prof. Thomas Kiørboe (National Institute of Aquatic Resources, Technical University of Denmark) (Nielsen and Kiørboe, 2015). A R. salina K‐1487 stock culture was maintained in f/2 medium (Guillard and Ryther, 1962; Guillard, 1975) without Na 2 SiO 3 but with 5 mM NH 4 Cl in 3% IO (Instant Ocean salts, Aquarium Systems Inc.) (f/2‐Si+NH 4 ) at 18°C and 24 μmol photons m −2  s −1 , photosynthetically active radiation (PAR).…”

Heterokont Predator Develorapax marinus gen. et sp. nov. – A Model of the Ochrophyte Ancestor

“…One of the difficulties with the latter evolutionary scenario is the apparent prevalence of bacterivory in close relatives of ochrophytes, which precludes the prerequisite for plastid acquisition – the ability to engulf eukaryotic prey. It was shown experimentally that there are optimum prey size spectra for various species of predatory protists ( Hansen, 1992 ; Jakobsen and Hansen, 1997 ; Montagnes et al, 2008 ; Nielsen and Kiørboe, 2015 ). Among recent heterotrophic and mixotrophic species there are those that are able to consume both bacterial and eukaryotic prey ( Strom, 1991 ; Burkholder et al, 2008 ; Piwosz and Pernthaler, 2010 ; Zhang et al, 2013 ; Lee et al, 2014 ; Mitra et al, 2016 ) while others are limited by the size of prey cells, with some eukaryotes lacking the ability to graze on bacteria ( Jonsson, 1986 ; Hansen and Calado, 1999 ; Montagnes et al, 2008 ).…”