Extended divergence estimates and species descriptions of new craspedid choanoflagellates from the Atacama Desert, Northern Chile

Protist communities of microbial mats from the extreme environments of five saline Andean lagoons at high altitudes in the Atacama Desert

Introduction

Heterotrophic protists colonizing microbial mats have received little attention over the last few years, despite their importance in microbial food webs. A significant challenge originates from the fact that many protists remain uncultivable and their functions remain poorly understood.

Methods

Metabarcoding studies of protists in microbial mats across high-altitude lagoons of different salinities (4.3-34 practical salinity units) were carried out to provide insights into their vertical stratification at the millimeter scale. DNA and cDNA were analyzed for selected stations.

Results

Sequence variants classified as the amoeboid rhizarian Rhogostoma and the ciliate Euplotes were found to be common members of the heterotrophic protist communities. They were accompanied by diatoms and kinetoplastids. Correlation analyses point to the salinity of the water column as a main driver influencing the structure of the protist communities at the five studied microbial mats. The active part of the protist communities was detected to be higher at lower salinities (<20 practical salinity units).

Discussion

We found a restricted overlap of the protist community between the different microbial mats indicating the uniqueness of these different aquatic habitats. On the other hand, the dominating genotypes present in metabarcoding were similar and could be isolated and sequenced in comparative studies (Rhogostoma, Euplotes, Neobodo). Our results provide a snapshot of the unculturable protist diversity thriving the benthic zone of five athalossohaline lagoons across the Andean plateau.

Novel cercozoan and heterolobosean protists from the rhizosphere and phyllosphere of two endemic cacti from the Atacama Desert

Cercozoans and heterolobose amoebae are found across terrestrial habitats where they feed on other unicellular microbes, including bacteria, fungi and microalgae. They constitute a significant fraction of soil ecosystems and are integral members of plant microbiota. Here, we present the results on the isolation of protozoans from the rhizosphere and phyllosphere of Browningia candelaris (Meyen) in the Andean Altiplano and Eulychnia taltalensis (F. Ritter) from the Coastal Cordillera of the Atacama Desert, both endemic to this ancient desert. We identified a new heterolobose amoeba species of the genus Allovahlkampfia isolated from cactus soil, three new species of the different glissomonad genera Allapsa, Neoheteromita, Neocercomonas and one new thecofilosean amoeba of the genus Rhogostoma isolated from the phyllosphere of one studied cactus. In addition, one bacterivorous flagellate was isolated from cactus spines and identified as a member of the non-scaled imbricatean family Spongomonadidae (Spongomonas). The isolation of protists from cactus spines extends the knowledge on the habitat ranges of taxa typically found on plant leaves or soils. The molecular data presented here is a prerequisite for further investigations on the ecology and diversity of protists including next-generation sequencing of microhabitats in plants and the rhizosphere, allowing for deeper taxonomic classification.

High diversity and isolated distribution of aquatic heterotrophic protists in salars of the Atacama Desert at different salinities

The species richness of eukaryotes in the hypersaline environment is generally thought to be low. However, recent studies showed a high degree of phylogenetic novelty at these extreme conditions with variable chemical parameters. These findings call for a more thorough look into the species richness of hypersaline environments. In this study, various hypersaline lakes (salars, 1-348 PSU) as well as further aquatic ecosystems of northern Chile were investigated regarding diversity of heterotrophic protists by metabarcoding studies of surface water samples. Investigations of genotypes of 18S rRNA genes showed a unique community composition in nearly each salar and even among different microhabitats within one salar. The genotype distribution showed no clear connection to the composition of main ions at the sampling sites, but protist communities from similar salinity ranges (either hypersaline, hyposaline or mesosaline) clustered together regarding their OTU composition. Salars appeared to be fairly isolated systems with only little exchange of protist communities where evolutionary lineages could separately evolve.

Re-evaluating Loricate Choanoflagellate Phylogenetics: Molecular Evidence Points to the Paraphyly of Tectiform Species

Lorica-bearing choanoflagellates belong to the order Acanthoecida, a taxon which has been consistently recovered as monophyletic in molecular phylogenies. Based upon differences in lorica development and morphology, as well as the presence or absence of a motile dispersal stage, species are labelled as either nudiform or tectiform. Whilst Acanthoecida is robustly resolved in molecular phylogenies, the placement of the root of the clade is less certain with two different positions identified in past studies. One recovered root has been placed between the nudiform family Acanthoecidae and the tectiform family Stephanoecidae. An alternative root placement falls within the tectiform species, recovering the monophyletic Acanthoecidae nested within a paraphyletic Stephanoecidae. Presented here is a 14-gene phylogeny, based upon nucleotide and amino acid sequences, which strongly supports tectiform paraphyly. The horizontal transfer of a ribosomal protein gene, from a possible SAR donor, into a subset of acanthoecid species provides further, independent, support for this root placement. Differing patterns of codon usage bias across the choanoflagellates are proposed as the cause of artefactual phylogenetic signals that lead to the recovery of tectiform monophyly.