Seasonal dynamics of culturable thraustochytrids (Labyrinthulomycetes, Stramenopiles) in estuarine and coastal waters

Abstract

Regular monitoring of estuarine and coastal areas at fixed points was carried out to investigate changes in biomass and species composition of thraustochytrids, which are colorless heterotrophs in the class Labyrinthulomycetes, Stramenopiles. Cell number counts using the most probable number (MPN) method with pine pollen baiting showed that 1 or 2 conspicuous peaks in abundance (termed 'thraustochytrid spikes') occurred between spring and late summer in most sampling years. Changes in thraustochytrid biomass had no correlation with phytoplankton abundance, although spikes seemed to occur after reductions in salinity and associated rapid rises of water temperature. The average cell density at the estuary site, excluding values during spike periods, was 4670 cells l −1 . Although thraustochytrid biomass was only 1.59% that of bacterial biomass, the fixed energy (as biomass) transferred directly from thraustochytrids to zooplankton was estimated to be 15.9% of that transferred from bacterioplankton via phagotrophic protists. This is because, per the theory of energy efficiency, energy transfer between trophic levels only creates 10% of the net production in the next trophic level relative to the first. The phylogenetic identification of established strains revealed an unexpectedly high diversity of thraustochytrids, including 10 unidentified lineages. A similar seasonal succession of phylogenetic groups was observed in each year of sampling. The differences in thraustochytrids isolated at each monitoring site and date suggest that habitat segregation may occur as a result of differences in environmental factors such as water temperature, salinity, and nutrient sources.

New Species of Saprobic Labyrinthulea (=Labyrinthulomycota) and the Erection of a gen. nov. to Resolve Molecular Polyphyly within the Aplanochytrids

“…Phylogenetically, our isolate groups among a number of undescribed thraustochytrids isolated in Japan (Ueda et al 2015), branching sister to isolates AR2-19 and M4-103. Based on molecular phylogeny, it is possible that Labyrinthulochytrium circumscribes these uncharacterized isolates; however, without life history information, we are unable to confidentially include these isolates within the Labyrinthulochytrium or concisely describe the evolutionary relationship of this genus to other genera.…”

“…Members of the Labyrinthulea are important decomposers of the detritus pool, whose abundance can exceed 10 3 cells per liter (Ueda et al. ). Members of the Labyrinthulea are morphologically distinct from other unicellular heterotrophic eukaryotes by the formation of an ectoplasmic net (Tsui et al.…”

“…THE Labyrinthulea (=Labyrinthulomycota) are cosmopolitan heterotrophs that behave as bacteriovores, saprotrophs, and symbionts in marine and freshwater ecosystems. Members of the Labyrinthulea are important decomposers of the detritus pool, whose abundance can exceed 10 3 cells per liter (Ueda et al 2015). Members of the Labyrinthulea are morphologically distinct from other unicellular heterotrophic eukaryotes by the formation of an ectoplasmic net (Tsui et al 2009) that is used to interface nutrient acquisition and motility (Bennett et al 2017).…”

Proposal of Monorhizochytrium globosum gen. nov., comb. nov. (Stramenopiles, Labyrinthulomycetes) for former Thraustochytrium globosum based on morphological features and phylogenetic relationships

“…The sterile seawater was transferred to 15‐mL tubes and centrifuged (670 × g for 5 min). The sediment was spread onto d‐GPY agar plates (Ueda et al ) supplemented with antibiotics (500 pmol μL −1 each of ampicillin and streptomycin). The remaining liquid, containing pine pollen, was incubated.…”

Reference Tree and Environmental Sequence Diversity of Labyrinthulomycetes

“…() and Ueda et al. () both attempted to uncover the hidden diversity of this group in marine samples, but they are also known to be abundant in freshwater and soil environments, especially in the Amphifilidae and Amphitremida. In addition, we currently lack an up‐to‐date reference database for the identification of Labyrinthulomycetes in ecological studies.…”