A cover of glass: first report of biomineralized silicon in a ciliate, Maryna umbrellata (Ciliophora: Colpodea)

Ciliated Peritrichous Protozoa in a Tezontle-Packed Sequencing Batch Reactor as Potential Indicators of Water Quality

The presence of colonial and solitary ciliated peritrichous protozoa was determined in a Sequencing Batch Reactor system filled with tezontle, a volcanic rock, economic, and abundant material that can be found in some parts of the world, like Mexico. The presence of these protozoa was related to the removal efficiencies of organic matter. Also, two novel staining techniques are proposed for staining both colonial and solitary peritrichous protozoa. The results show that tezontle promotes the growth of solitary and colonial ciliated peritrichous protozoa, which, once identified, could be used as indicators of the efficiency of the wastewater treatment process. Additionally, the staining techniques established in the current study allowed the precise observation of protozoan nuclei. They can represent a useful complementary methodology for identifying protozoan species present in water treatment processes, along with the already existing identification techniques. The number and variety of protozoa found in the system may be considered potential bioindicators of water quality during biological treatments.

A light and electron microscopical study on the resting cyst of the tintinnid Schmidingerella (Alveolata, Ciliophora) including a phylogeny-aware comparison

Resting cysts protect ciliates against adverse environmental conditions. The morphology and ultrastructure of resting cysts has been described in very few Oligotrichea, a group of mainly marine planktonic ciliates. The present study provides the first ultrastructural data for loricate choreotrichids, applying light and electron microscopy on the cysts of the tintinnid Schmidingerella meunieri (Kofoid and Campbell, 1929) Agatha and Strüder-Kypke, 2012. The morphology of live cysts and the wall ultrastructure of cryofixed cysts were morphometrically analysed. The resting cyst is roughly flask-shaped, broadening to a slightly concave, laterally protruding anterior plate. An emergence pore closed by a skull cap-shaped papula is directed to the bottom of the lorica on the opposite side of the cyst. The cyst wall consists of an ectocyst, mesocyst, and endocyst differing in thickness, structure, and nitrogen concentration as revealed by conventional transmission electron microscopy, electron energy loss spectroscopy, and electron spectroscopic imaging. The cysts of S. meunieri belong to the kinetosome-resorbing type, which also occurs in the majority of hypotrich ciliates. Two main features (flask-shape and presence of an emergence pore) are shared with the closely related aloricate choreotrichids and oligotrichids, distinguishing the Oligotrichea from the hypotrich and the more distantly related euplotid ciliates.

The Evolution of Silicon Transport in Eukaryotes

Biosilicification (the formation of biological structures from silica) occurs in diverse eukaryotic lineages, plays a major role in global biogeochemical cycles, and has significant biotechnological applications. Silicon (Si) uptake is crucial for biosilicification, yet the evolutionary history of the transporters involved remains poorly known. Recent evidence suggests that the SIT family of Si transporters, initially identified in diatoms, may be widely distributed, with an extended family of related transporters (SIT-Ls) present in some nonsilicified organisms. Here, we identify SITs and SIT-Ls in a range of eukaryotes, including major silicified lineages (radiolarians and chrysophytes) and also bacterial SIT-Ls. Our evidence suggests that the symmetrical 10-transmembrane-domain SIT structure has independently evolved multiple times via duplication and fusion of 5-transmembrane-domain SIT-Ls. We also identify a second gene family, similar to the active Si transporter Lsi2, that is broadly distributed amongst siliceous and nonsiliceous eukaryotes. Our analyses resolve a distinct group of Lsi2-like genes, including plant and diatom Si-responsive genes, and sequences unique to siliceous sponges and choanoflagellates. The SIT/SIT-L and Lsi2 transporter families likely contribute to biosilicification in diverse lineages, indicating an ancient role for Si transport in eukaryotes. We propose that these Si transporters may have arisen initially to prevent Si toxicity in the high Si Precambrian oceans, with subsequent biologically induced reductions in Si concentrations of Phanerozoic seas leading to widespread losses of SIT, SIT-L, and Lsi2-like genes in diverse lineages. Thus, the origin and diversification of two independent Si transporter families both drove and were driven by ancient ocean Si levels.

The evolution of silicon transporters in diatoms

Diatoms are highly productive single-celled algae that form an intricately patterned silica cell wall after every cell division. They take up and utilize silicic acid from seawater via silicon transporter (SIT) proteins. This study examined the evolution of the SIT gene family to identify potential genetic adaptations that enable diatoms to thrive in the modern ocean. By searching for sequence homologs in available databases, the diversity of organisms found to encode SITs increased substantially and included all major diatom lineages and other algal protists. A bacterial-encoded gene with homology to SIT sequences was also identified, suggesting that a lateral gene transfer event occurred between bacterial and protist lineages. In diatoms, the SIT genes diverged and diversified to produce five distinct clades. The most basal SIT clades were widely distributed across diatom lineages, while the more derived clades were lineage-specific, which together produced a distinct repertoire of SIT types among major diatom lineages. Differences in the predicted protein functional domains encoded among SIT clades suggest that the divergence of clades resulted in functional diversification among SITs. Both laboratory cultures and natural communities changed transcription of each SIT clade in response to experimental or environmental growth conditions, with distinct transcriptional patterns observed among clades. Together, these data suggest that the diversification of SITs within diatoms led to specialized adaptations among diatoms lineages, and perhaps their dominant ability to take up silicic acid from seawater in diverse environmental conditions.

Peptide-catalyzed, bioinspired silicification for single-cell encapsulation in the imidazole-buffered system

Cytoprotective silica encapsulation of individual yeast cells is achieved by a peptide-catalyzed silicification under mild conditions, inspired by glass sponges.

Artificial spores: cytocompatible encapsulation of individual living cells within thin, tough artificial shells

Cells are encapsulated individually within thin and tough shells in a cytocompatible way, by mimicking the structure of bacterial endospores that survive under hostile conditions. The 3D 'cell-in-shell' structures-coined as 'artificial spores'-enable modulation and control over cellular metabolism, such as control of cell division, resistance to external stresses, and surface-functionalizability, providing a useful platform for applications, including cell-based sensors, cell therapy, regenerative medicine, as well as for fundamental studies on cellular metabolism at the single-cell level and cell-to-cell communications. This Concept focuses on chemical approaches to single-cell encapsulation with artificial shells for creating artificial spores, including cross-linked layer-by-layer assembly, bioinspired mineralization, and mussel-inspired polymerization. The current status and future prospects of this emerging field are also discussed.

A silicon cell cycle in a bacterial model of calcium phosphate mineralogenesis

The prokaryote Corynebacterium matruchotii produces calcium phosphate (bone salt) and may serve as a convenient model for examining individual factors relevant to vertebrate calcification. A factor of current clinical uncertainty is silicon. To investigate its possible role in biomineralisation advanced optical (digital deconvolution and 3D fluorescent image rendering) and electron microscopy (EDX microanalysis and elemental mapping) were applied to calcifying microbial colonies grown in graded Si concentrations (0-60mM). Cell viability was confirmed throughout by TO-PRO-3-iodide and SYTO-9 nucleic acid staining. It was observed that calcium accumulated in dense intracellular microspherical objects (types i-iii) as nanoparticles (5 nm, type i), nanospheres (30-50 nm, type ii) and filamentous clusters (0.1-0.5 μm, type iii), with a regular transitory Si content evident. With bacterial colony development (7-28 days) the P content increased from 5 to 60%, while Si was displaced from 60 to 5%, distinguishing the phenomenon from random contamination, and with a significant relationship (p<0.001) found between calcified object number and Si supplementation (optimum 0.01mM). The Si-containing, intracellular calcified objects (also positive for Mg and negative with Lysensor blue DND-167 for acidocalcisomes) were extruded naturally in bubble-like chains to complete the cycle by coating the cell surface with discrete mineral particles. These could be harvested by lysis, French press and density fractionation when Si was confirmed in a proportion. It was concluded that the unexplained orthopaedic activity of Si may derive from its special property to facilitate calcium phosphorylation in biological systems, thereby recapitulating an ancient and conserved bacterial cycle of calcification via silicification.

Intraclass evolution and classification of the Colpodea (Ciliophora)

Using nine new taxa and statistical inferences based on morphological and molecular data, we analyze the evolution within the class Colpodea. The molecular and cladistic analyses show four well-supported clades: platyophryids, bursariomorphids, cyrtolophosidids, and colpodids. There is a widespread occurrence of homoplasies, affecting even conspicuous morphological characteristics, e.g. the inclusion of the micronucleus in the perinuclear space of the macronucleus. The most distinct changes in the morphological classification are the lack of a basal divergence into two subclasses and the split of the cyrtolophosidids into two main clades, differing mainly by the presence vs. absence of an oral cavity. The most complex clade is that of the colpodids. We partially reconcile the morphological and molecular data using evolutionary systematics, providing a scenario in which the colpodids evolved from a Bardeliella-like ancestor and the genus Colpoda performed an intense adaptive radiation, giving rise to three main clades: Colpodina n. subord., Grossglockneriina, and Bryophryina. Three new taxa are established: Colpodina n. subord., Tillinidae n. fam., and Ottowphryidae n. fam. Colpodean evolution and classification are far from being understood because sequences are lacking for most species and half of their diversity is possibly undescribed.

Experimental evolution of protozoan traits in response to interspecific competition

Decades of experiments have demonstrated the ecological effect of competition, but experimental evidence for competitive effects on trait evolution is rare. I measured the evolution of six protozoan traits in response to competitors from the inquiline community of pitcher plants. Replicate populations of Colpoda, a ciliated protozoan, were allowed to evolve in response to intra- and interspecific competition for 20 days (approximately 100 generations), before traits were measured in two common garden environments. Populations that evolved with interspecific competition had smaller cell sizes, produced fewer cysts and had higher population growth rates relative to populations grown in monoculture. The presence of interspecific competitors led to differential lineage sorting, most likely by increasing the strength of selection. These results are the first to demonstrate protozoan evolution in response to competition and may have implications for species coexistence in this system.

The Stunning, Glass-Covered Resting Cyst of Maryna umbrellata (Ciliophora, Colpodea)

Maryna umbrellata (Gelei, 1950) Foissner, 1993 is a colpodid ciliate common in ephemeral water bodies. Pure cultures were established and the resting cyst studied by light and electron microscopy, protease digestion of thin sections, and various cytochemical reactions shown by colour micrographs. The cyst of M. umbrellata belongs to the kinetosome-resorbing (KR) type and has a conspicuous glass cover described by Foissner et al. (2009). It is 100 μm across and the about 13 μm thick wall, which amounts for half of the total cyst volume, consists of four distinct layers: (i) the about 6 μm thick pericyst, which is composed of glass granules embedded in mucoproteins, and of a basal layer consisting of glycogen tubules about 20 nm across; (ii) the about 140 nm thick, electron-dense ectocyst, which is not digested by protease; (iii) the about 6 μm thick mesocyst, which is distinctly laminated and made of proteins; and (iv) the thin, about 500 nm thick endocyst, which is structureless and consists of glycoproteins. The meso- and endocyst are highly elastic, reducing their diameter by 50% when the encysted ciliate is removed. The cyst contents is dominated by up to 7 μm-sized "spongy globules" consisting of an electron-dense, proteinaceous matrix burrowed by electron-lucent strands of glycogen, providing the cyst with a curious, white-spotted appearance in the electron microscope. The small lipid droplets have a proteinaceous centre. The cyst plasm contains proteins and unstructured mucosubstances, which stain with alcian blue, and thus possibly originate from the decomposed mucocysts. This study suggests that ciliate resting cysts are much more diverse than indicated by literature data.