Mixotrophic Activity and Diversity of Antarctic Marine Protists in Austral Summer

Abstract

Identifying putative mixotrophic protist species in the environment is important for understanding their behavior, with the recovery of these species in culture essential for determining the triggers of feeding, grazing rates, and overall impact on bacterial standing stocks. In this project, mixotroph abundances determined using tracer ingestion in water and sea ice samples collected in the Ross Sea, Antarctica during the summer of 2011 were compared with data from the spring (Ross Sea) and fall (Arctic) to examine the impacts of bacterivory/mixotrophy. Mixotrophic nanoplankton (MNAN) were usually less abundant than heterotrophs, but consumed more of the bacterial standing stock per day due to relatively higher ingestion rates (1-7 bacteria mixotroph −1 h −1 vs. 0.1-4 bacteria heterotroph −1 h −1 ). Yet, even with these high rates observed in the Antarctic summer, mixotrophs appeared to have a smaller contribution to bacterivory than in the Antarctic spring. Additionally, putative mixotroph taxa were identified through incubation experiments accomplished with bromodeoxyuridine-labeled bacteria as food, immunoprecipitation (IP) of labeled DNA, and amplification and high throughput sequencing of the eukaryotic ribosomal V9 region. Putative mixotroph OTUs were identified in the IP samples by taxonomic similarity to known phototroph taxa. OTUs that had increased abundance in IP samples compared to the non-IP samples from both surface and chlorophyll maximum (CM) depths were considered to represent active mixotrophy and include ones taxonomically similar to Dictyocha, Gymnodinium, Pentapharsodinium, and Symbiodinium. These OTUs represent target taxa for isolation and laboratory experiments on triggers for mixotrophy, to be combined with qPCR to estimate their abundance, seasonal distribution and potential impact.

On the Relationship between a Novel Prorocentrum sp. and Colonial Phaeocystis antarctica under Iron and Vitamin B12 Limitation: Ecological Implications for Antarctic Waters

“…Of the mixotrophic species, food vacuoles or prey ingestion have been observed in Prorocentrales, particularly in Prorocentrum minimum [72], and the host species of dinoflagellates within the mucilaginous colonies of P. antarctica have been previously reported [30,73]. In addition, a novel dinoflagellate, related to the ichthyotoxic genera Karenia and Karlodinium, discovered in the Ross Sea by [74] was closely related to the free-living, unicellular P. antarctica. Although it is not clear if kleptoplastic dinoflagellates prefer colonial or unicellular stages of P. antarctica as the plastid source [30,31], the important ecological role of mixotrophy in providing access to limiting nutrients has long been recognized [75][76][77], as it has significantly impacted prey populations in marine microbial food webs.…”

Importance of mixotrophic flagellates during the ice-free season in lakes located along an elevational gradient

“…Nevertheless, mixotrophic species differ in their dependence on light and some taxa are known to grow in the dark when enough food is available, as well as many taxa, can grow in light without feeding (Jones 2000 ). Obviously, information on taxonomic identity of mixotrophic taxa and physiological experiments with isolates (Gast et al 2018 ), as well as combination of different approaches (see for a review Beisner et al 2019 ) are needed to understand what environmental factors are relevant in the field.…”

Ocean acidification reduces growth and grazing impact of Antarctic heterotrophic nanoflagellates

“…There is an increased understanding of the prevalence of mixotrophy in the marine microbial community (Mitra et al, 2014;Stoecker et al, 2017;Gast et al, 2018). There-fore, it is possible that mixotrophic nanoflagellates were included in our nanophytoplankton counts due to the presence of chlorophyll in their cells.…”