Environmental drivers of plankton protist communities along latitudinal and vertical gradients in the oldest and deepest freshwater lake

Abstract

Summary Identifying which abiotic and biotic factors determine microbial community assembly is crucial to understand ecological processes and predict how communities will respond to environmental change. While global surveys aim at addressing this question in the world's oceans, equivalent studies in large freshwater systems are virtually lacking. Being the oldest, deepest and most voluminous freshwater lake on Earth, Lake Baikal offers a unique opportunity to test the effect of horizontal versus vertical gradients in community structure. Here, we characterized the structure of planktonic microbial eukaryotic communities (0.2–30 μm cell size) along a North–South latitudinal gradient (~600 km) from samples collected in coastal and pelagic waters and from surface to the deepest zones (5–1400 m) using an 18S rRNA gene metabarcoding approach. Our results show complex and diverse protist communities dominated by alveolates (ciliates and dinoflagellates), ochrophytes and holomycotan lineages, with cryptophytes, haptophytes, katablepharids and telonemids in moderate abundance and many low‐frequency lineages, including several typical marine members, such as diplonemids, syndinians and radiolarians. Depth had a strong significant effect on protist community stratification. By contrast, the effect of the latitudinal gradient was marginal and no significant difference was observed between coastal and surface open water communities. Co‐occurrence network analyses showed that epipelagic communities were significantly more interconnected than communities from the dark water column and suggest specific biotic interactions between autotrophic, heterotrophic and parasitic lineages that influence protist community structure. Since climate change is rapidly affecting Siberia and Lake Baikal, our comprehensive protist survey constitutes a useful reference to monitor ongoing community shifts.

Molecular and morphological characterization of four new ancyromonad genera and proposal for an updated taxonomy of the Ancyromonadida

“…We searched for ancyromonad sequences in the PR2, Silva, and GenBank “nr” nucleotide databases, and retrieved 178 environmental 18S rDNA sequences (Table S2). In addition, we retrieved 146 ancyromonad sequences from five recent protist metabarcoding studies: three from freshwater (David, López‐García, et al, 2021, David, Moreira, et al, 2021; Iniesto et al, 2021) and two from marine environments (Logares et al, 2020; Massana et al, 2015). Finally, we obtained nine additional environmental sequences from previously sampled marine and freshwater environments (Torruella et al, 2017) by PCR amplification of 18S rRNA genes using ancyromonad‐specific primer pairs (Table S3), cloning, and sequencing.…”

“…We identified 207 sequences: 29 from previously characterized ancyromonads and 178 from environmental sources (Table S2). Similarly, ancyromonad sequences were mined from five metabarcoding studies based on the v4 region of the 18S rRNA gene, including three studies from freshwater (David, López‐García, et al, 2021; David, Moreira, et al, 2021; Iniesto et al, 2021), and two from marine environments (Logares et al, 2020; Massana et al, 2015), yielding 146 OTUs (Table S2).…”

Local-Scale Damming Impact on the Planktonic Bacterial and Eukaryotic Communities in the Upper Yangtze River

“…Cyanobium_PCC-6307 (belonging to Cyanobacteria) attained a higher relative abundance in the XLD and XJB Dams, while this organism was not dominant in the TGD, which may be related to the operating conditions of the reservoir. Among the eukaryotic communities, Mediophyceae (belonging to Stramenopiles) and Arthropoda (belonging to Bilateria) were dominant, both of which are also common eukaryotes in freshwater ecosystems [29,50,51].…”

Molecular and morphological characterisation of four new ancyromonad genera and proposal for an updated taxonomy of the Ancyromonadida

“…We identified 207 sequences: 29 from previously characterised ancyromonads and 178 from environmental sources (Table S2). Similarly, ancyromonad sequences were mined from five metabarcoding studies based on the v4 region of the 18S rRNA gene, including three studies from freshwater (David et al, 2021a(David et al, , 2021bIniesto et al, 2021), and two from marine environments (Logares et al, 2020;Massana et al, 2015), resulting in 146 OTUs (Table S2).…”