Protist最新文献

Species richness is a key ecological characteristic that influences numerous ecosystem functions. Here we analyse the patterns and possible causes of phytoplankton taxon richness in seasonal datasets from twenty contrasting lakes in the English Lake District over six years and near-weekly datasets over 33 years from Windermere. Taxon richness was lowest in winter and highest in summer or autumn in all of the lakes. Observed richness was very similar to richness estimated from coverage and sampling effort, implying that it closely reflected true seasonal patterns. Summer populations were dominated by Chlorophyta and functional groups X1, F, N and P (sensu Reynolds). In Windermere, weekly taxon richness was strongly positively correlated with surface water temperature, as was the number of functional groups and the number of taxa per functional group. Turnover in richness of taxa and functional groups were positively correlated and both were related to surface temperature. This suggests that high taxon richness in summer is linked to higher water temperature, promoting a turnover in richness of taxa and functional groups in these lakes. However, since the number of taxa per unit concentration of chlorophyll a decreased with increasing concentration of chlorophyll a, competition might occur when abundance is high.

With his scientific curiosity and deep understanding of unicellular organisms, Bland J. Finlay could demonstrate that water bodies as small and innocuous as “Priest Pot“ in the English Lake District represent a very broad range of protists and their interactions. From this, not only the field of protistan ecology benefitted greatly, but also my personal career. Enclosed are some scientific and personal memories to say ”thank you” to Bland.

To explore the potential of urban settings as habitats for testate amoebae, five historical parks in Potsdam (Germany) were sampled at different sites. A total of 32 sampling sites was chosen in proximity to deciduous (Acer, Castanea, Fagus, Tilia, Platanus, Quercus) and coniferous (Fraxinus, Picea, Pinus, Tsuga) trees. Meadows and creeks were also sampled. The overall taxonomic record comprises 76 species and sub-species. High species numbers of >20 per sample were found in meadows and below Fagus, Tilia, and Quercus trees. The species richness per park ranges from 33 to 46 taxa. Most species belong to the eurybiontic ecological group, although litter-inhabiting and hygrophilic and hydrophilic species were also present. Common species found in more than 50% of all samples (superdominants) belong to the genera Centropyxis, Cyclopyxis, Euglypha, and Trinema. Interestingly, the rare Frenopyxis stierlitzi which inhabits tree hollows was found as a recently described species in a new genus Frenopyxis Bobrov & Mazei 2020 in the Babelsberg Park. The studied testate amoebae are characterized by a high degree of morphological and morphometric plasticity. Therefore, the study of testate amoebae in urban settings will reveal new insights into their ecology and enhance the definition of morphometric variability for single species.

Cryopreservation, the use of very low temperatures to preserve structurally intact living cells and tissues, is a key underpinning technology for life science research and medicine. It is employed to ensure the stability of critical biological resources including viruses, bacteria, protists, animal cell cultures, plants, reproductive materials and embryos. Fundamental to ensuring this stability is assuring stability of cryogenic storage temperatures. Here we report the occurrence of a failure in refrigeration in a cryostat holding > 600 strains of cyanobacteria and eukaryotic microalgae. A strategic approach was adopted to assess viability across a cross-section of the biodiversity held, both immediately after the potentially damaging temperature shift and 10 years later, on subsequent cryostorage in liquid-phase nitrogen (∼−196 °C). Furthermore, the event was replicated experimentally and the effects on the viability of cryo-tolerant and cryo-sensitive strains monitored. Our results have significant implications to all users of this storage method and parallels have been drawn with the ongoing development in other fields and in particular, human cell therapy. Based on our practical experience we have made a series of generic recommendations for emergency, remedial and ongoing preventative actions.

The deposition of silicified costal strips and lorica assembly in choanoflagellates is precisely linked to the cell cycle. A minority of species undergo nudiform division whereby a loricate cell divides to produce a naked daughter cell that deposits a set of costal strips and then assembles a lorica. Most species undergo tectiform division whereby a parent loricate cell produces a set of costal strips, divides and passes on the stored strips to a daughter cell that immediately assembles a lorica. Many phylogenetic analyses recover nudiform and tectiform species as sister-clades giving the impression that they are distinct evolutionary lineages. However, the tectiform species Stephanoeca diplocostata is capable of undergoing nudiform division and depositing costal strips and assembling a lorica with certain modifications in a nudiform manner. The recent discovery of a new genus, Enibas, comprising species with Stephanoeca-like loricae that undergo nudiform cell division and on phylogenetic analysis occur as a sister group to other nudiform species has drawn attention to whether there are also unique features in lorica construction. A range of Enibas loricae is illustrated and it appears that there are unique features which might be interpreted as being derived from a Stephanoeca-like ancestor.

In a field experiment we investigated the influence of the environmental filters soil type (i.e. three contrasting soils) and plant species (i.e. lettuce and potato) identity on rhizosphere community assembly of Cercozoa, a dominant group of mostly bacterivorous soil protists. Plant species (14%) and rhizosphere origin (vs bulk soil) with 13%, together explained four times more variation in cercozoan beta diversity than the three soil types (7% explained variation). Our results clearly confirm the existence of plant species-specific protist communities. Network analyses of bacteria-Cercozoa rhizosphere communities identified scale-free small world topologies, indicating mechanisms of self-organization. While the assembly of rhizosphere bacterial communities is bottom-up controlled through the resource supply from root (secondary) metabolites, our results support the hypothesis that the net effect may depend on the strength of top-down control by protist grazers. Since grazing of protists has a strong impact on the composition and functioning of bacteria communities, protists expand the repertoire of plant genes by functional traits, and should be considered as ‘protist microbiomes’ in analogy to ‘bacterial microbiomes’.

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.

An angled twin–layer porous substrate photobioreactor (TL-PSBR) using LED light was designed to cultivate Nannochloropsis oculata. Flocculation and sedimentation by modification of pH to 11 were determined as the optimal method for harvesting the N. oculata inoculum. The following optimised parameters were found: tilt angle 15°, Kraft 220 g m⁻² paper as substrate material, initial inoculum density of 12.5 g m⁻², 140 µmol photons m⁻² s⁻¹ light intensity, and a light/dark cycle of 6:6 (h). Test cultivation for 14 days was performed under optimised conditions. The total dried biomass standing crop was 75.5 g m⁻² growth area with an average productivity of 6.3 g m⁻² d⁻¹, the productivity per volume of used culture medium was 126.2 mg/L d⁻¹, total lipid content 21.9% (w/w), and the highest productivity of total lipids was 1.33 g m⁻² d⁻¹. The dry algal biomass contained 3% eicosapentaenoic acid (w/w), 3.7% palmitoleic acid (w/w), and 513 mg kg⁻¹ vitamin E. The optimisation of N. oculata cultivation on an angled TL-PSBR system yielded promising results, and applications for commercial products need to be further explored.