The structure and the formation of egg shells in the parthenogenetic species Dactylobiotus dispar Murray, 1907 (Tardigrada: Eutardigrada)

The eggs of Dactylobiotus dispar, similar to other Tardigrada eggs, are covered with two shells: the vitelline envelope and the chorion. Ultrastructural studies have shown that the oocyte actively participates in the formation of both shells. The process of egg capsule formation begins at the midpoint of vitellogenesis. The chorion at first appears as isolated cones resulting from the exocytotic activity of the oocyte and the ovarian epithelium. Subsequently, connections between the cones are formed. Three layers can be distinguished in the completely developed chorion: (1) the inner layer of medium electron density; (2) the middle, labyrinthine layer; (3) the outer layer of medium electron density with cones (future conical processes). After chorion formation, a vitelline envelope is secreted by the oocyte. The Dactylobiotus dispar egg is covered with small, conical processes with hooked tips. The surface of the chorion is covered with a mesh-like network consisting of elongated interstices. The egg capsule has no micropylar opening

Structure and ultrastructure of the egg capsule of Thermobia domestica (Packard) (Insecta, Zygentoma)

Eggs of Thermobia domestica (Packard) were collected from a laboratory culture. They were prepared for analysis in light and electron microscopes (TEM, SEM). A few hours after oviposition the egg capsule starts to tarnish and changes its colour to brown. Polygonic shapes on its surface can be seen. The egg capsule consists of a thin vitelline envelope and the chorion. The chorion consists of a one-layered endochorion and a three-layered exochorion. There are minor and major mushroom-like structures placed on the surface of the chorion. Their function is proposed. One micropyle is observed on the anterior pole of the egg. The micropylar opening is formed on the process of a follicular cell

Analysis of Encystment, Excystment, and Cyst Structure in Freshwater Eutardigrade Thulinius ruffoi (Tardigrada, Isohypsibioidea: Doryphoribiidae)

Encystment in tardigrades is relatively poorly understood. It is seen as an adaptive strategy evolved to withstand unfavorable environmental conditions. This process is an example of the epigenetic, phenotypic plasticity which is closely linked to the molting process. Thulinius ruffoi is a freshwater eutardigrade and a representative of one of the biggest eutardigrade orders. This species is able to form cysts. The ovoid-shaped cysts of this species are known from nature, but cysts may also be obtained under laboratory conditions. During encystment, the animals undergo profound morphological changes that result in cyst formation. The animals surround their bodies with cuticles that isolate them from the environment. These cuticles form a cuticular capsule (cyst wall) which is composed of three cuticles. Each cuticle is morphologically distinct. The cuticles that form the cuticular capsule are increasingly simplified. During encystment, only one, unmodified and possibly functional buccal-pharyngeal apparatus was found to be formed. Apart from the feeding apparatus, the encysted specimens also possess a set of claws, and their body is covered with its own cuticle. As a consequence, the encysted animals are fully adapted to the active life after leaving the cyst capsule

The role of autophagy in the midgut epithelium of Parachela (Tardigrada)

The process of cell death has been detected in the midgut epithelium of four tardigrade species which belong to Parachela: Macrobiotus diversus, Macrobiotus polonicus, Hypsibius dujardini and Xerobiotus pseudohufelandi. They originated from different environments so they have been affected by different stressors: M. polonicus was extracted from a moss sample collected from a railway embankment; M. diversus was extracted from a moss sample collected from a petrol station; X. pseudohufelandi originated from sandy and dry soil samples collected from a pine forest; H. dujardini was obtained commercially but it lives in a freshwater or even in wet terrestrial environment. Autophagy is caused in the digestive cells of the midgut epithelium by different factors. However, a distinct crosstalk between autophagy and necrosis in tardigrades’ digestive system has been described at the ultrastructural level. Apoptosis has not been detected in the midgut epithelium of analyzed species. We also determined that necrosis is the major process that is responsible for the degeneration of the midgut epithelium of tardigrades, and “apoptosis–necrosis continuum” which is the relationship between these two processes, is disrupted

A comparative ultrastructure study of storage cells in the eutardigrade Richtersius coronifer in the hydrated state and after desiccation and heating stress

Tardigrades represent an invertebrate phylum with no circulatory or respiratory system. Their body cavity is filled with free storage cells of the coelomocyte-type, which are responsible for important physiological functions. We report a study comparing the ultrastructure of storage cells in anhydrobiotic and hydrated specimens of the eutardigrade Richtersius coronifer. We also analysed the effect of temperature stress on storage cell structure. Firstly, we verified two types of ultrastructurally different storage cells, which differ in cellular organelle complexity, amount and content of reserve material and connection to oogenetic stage. Type I cells were found to differ ultrastructurally depending on the oogenetic stage of the animal. The main function of these cells is energy storage. Storage cells of Type I were also observed in the single male that was found among the analysed specimens. The second cell type, Type II, found only in females, represents young undifferentiated cells, possibly stem cells. The two types of cells also differ with respect to the presence of nucleolar vacuoles, which are related to oogenetic stages and to changes in nucleolic activity during oogenesis. Secondly, this study revealed that storage cells are not ultrastructurally affected by six months of desiccation or by heating following this desiccation period. However, heating of the desiccated animals (tuns) tended to reduce animal survival, indicating that long-term desiccation makes these animals more vulnerable to heat stress. We confirmed the degradative pathways during the rehydration process after desiccation and heat stress. Our study is the first to document two ultrastructurally different types of storage cells in tardigrades and reveals new perspectives for further studies of tardigrade storage cells

The fine structure of the midgut epithelium in Xerobiotus pseudohufelandi (Iharos, 1966) (Tardigrada, Eutardigrada, Macrobiotidae)

The aims of our studies were to describe the ultrastructure of the midgut epithelial cells of the eutardigrade Xerobiotus pseudohufelandi and to determine if there are any differences in the ultrastructure of midgut epithelial cells between males and females. The analysis was performed with the use of the light and transmission electron microscopes. In X. pseudohufelandi the midgut epithelium is composed of digestive cells, but in the anterior portion of the midgut a group of cells with different ultrastructure has been observed. Histochemical staining showed the accumulation of reserve material in the cytoplasm of digestive cells. We suggest that some of them fulfil the role of regenerative cells (crescent-like cells, midgut stem cells), whereas others are differentiating cells which form new digestive cells. No differences in the ultrastructure of the midgut epithelium between males and females were distinguished except in the amount of multivesicular bodies

Kryptobioza i encystacja niesporczaków jako odpowiedź na czynniki stresu środowiskowego

tekst w j. pol. i ang.Analiza odpowiedzi niesporczaków na działanie wybranych stresorów środowiskowych

Ecophysiology and dynamics of nitrogen removal bacteria in a sequencing batch reactor during wastewater treatment start‑up

Nitrogen removal communities performing wastewater treatment consist of ammonia oxidisers, nitrite oxidisers, denitrifiers, and anammox bacteria, and the proportion and activity of particular microbial groups depend not only on the physiochemical parameters of the bioreactor, but also on the composition of the inoculum. Nitrifiers and denitrifiers usually dominate in conventional wastewater treatment systems due to the fact that nitrification and denitrification are the most commonly used nitrogen removal processes. However, from the economical point of view in case of wastewater with high ammonia concentrations, anammox-based technologies are desirable for their treatment. The disadvantage of such systems is slow anammox bacteria growth, which extends an effective technological start-up. Thus, in this study, a fast start-up of the anammox process supported with an anammox-rich inoculum was performed in a sequencing batch reactor (SBR). Using anammox inoculation of SBR laboratory system, the start-up can be fastened to 85 days with 84.5% of nitrogen removal efficacy. The spatial distribution of nitrogen removal bacteria analysed with fluorescent in situ hybridisation revealed that anammox and nitrifiers are located side by side in the flocs and the relative number of ammonia and nitrite oxidisers decreased after 85 days of the experiment

Differentiation of regenerative cells in the midgut epithelium of epilachna cf. nylanderi (Mulsant 1850) (insecta, coleoptera, coccinellidae)

Differentiation of regenerative cells in the midgut epithelium of Epilachna cf. nylanderi (Mulsant 1850) (Insecta, Coleoptera, Coccinellidae), a consumer of the Ni-hyperaccumulator Berkheya coddii (Asteracae) from South Africa, has been monitored and described. Adult specimens in various developmental phaseswere studiedwith the use of lightmicroscopy and transmission electron microscopy. All degenerated epithelial cells are replaced by newly differentiated cells. They originate from regenerative cells which act as stem cells in the midgut epithelium. Just after pupal-adult transformation, the midgut epithelium of E. nylanderi is composed of columnar epithelial cells and isolated regenerative cells distributed among them. The regenerative cells proliferate intensively and form regenerative cell groups. In each regenerative cell group the majority of cells differentiate into new epithelial cells, while some of them still act as stem cells and persist as a reservoir of cells capable for proliferation and differentiation. Because this species is an obligate monophage of plants which accumulate nickel, proliferation and differentiation

Selective neuronal staining in tardigrades and onychophorans provides insights into the evolution of segmental ganglia in panarthropods

Background: Although molecular analyses have contributed to a better resolution of the animal tree of life, the phylogenetic position of tardigrades (water bears) is still controversial, as they have been united alternatively with nematodes, arthropods, onychophorans (velvet worms), or onychophorans plus arthropods. Depending on the hypothesis favoured, segmental ganglia in tardigrades and arthropods might either have evolved independently, or they might well be homologous, suggesting that they were either lost in onychophorans or are a synapomorphy of tardigrades and arthropods. To evaluate these alternatives, we analysed the organisation of the nervous system in three tardigrade species using antisera directed against tyrosinated and acetylated tubulin, the amine transmitter serotonin, and the invertebrate neuropeptides FMRFamide, allatostatin and perisulfakinin. In addition, we performed retrograde staining of nerves in the onychophoran Euperipatoides rowelli in order to compare the serial locations of motor neurons within the nervous system relative to the appendages they serve in arthropods, tardigrades and onychophorans. Results: Contrary to a previous report from a Macrobiotus species, our immunocytochemical and electron microscopic data revealed contralateral fibres and bundles of neurites in each trunk ganglion of three tardigrade species, including Macrobiotus cf. harmsworthi, Paramacrobiotus richtersi and Hypsibius dujardini. Moreover, we identified additional, extra-ganglionic commissures in the interpedal regions bridging the paired longitudinal connectives. Within the ganglia we found serially repeated sets of serotonin- and RFamid-like immunoreactive neurons. Furthermore, our data show that the trunk ganglia of tardigrades, which include the somata of motor neurons, are shifted anteriorly with respect to each corresponding leg pair, whereas no such shift is evident in the arrangement of motor neurons in the onychophoran nerve cords. Conclusions: Taken together, these data reveal three major correspondences between the segmental ganglia of tardigrades and arthropods, including (i) contralateral projections and commissures in each ganglion, (ii) segmentally repeated sets of immunoreactive neurons, and (iii) an anteriorly shifted (parasegmental) position of ganglia. These correspondences support the homology of segmental ganglia in tardigrades and arthropods, suggesting that these structures were either lost in Onychophora or, alternatively, evolved in the tardigrade/arthropod lineage