Intrageneric Variability Between the Chloroplast Genomes of Trachelomonas grandis and Trachelomonas volvocina and Phylogenomic Analysis of Phototrophic Euglenoids

The latest studies of chloroplast genomes of phototrophic euglenoids yielded different results according to intrageneric variability such as cluster arrangement or diversity of introns. Although the genera Euglena and Monomorphina in those studies show high syntenic arrangements at the intrageneric level, the two investigated Eutreptiella species comprise low synteny. Furthermore Trachelomonas volvocina show low synteny to the chloroplast genomes of the sister genera Monomorphina aenigmatica, M. parapyrum, Cryptoglena skujae, Euglenaria anabaena, Strombomonas acuminata, all of which were highly syntenic. Consequently, this study aims at the analysis of the cpGenome of Trachelomonas grandis and a comparative examination of T. volvocina to investigate whether the cpGenomes are of such resemblance as could be expected for a genus within the Euglenaceae. Although these analyses resulted in almost identical gene content to other Euglenaceae, the chloroplast genome showed significant novelties: In the rRNA operon, we detected group II introns, not yet found in any other cpGenome of Euglenaceae and a substantially heterogeneous cluster arrangement in the genus Trachelomonas. The phylogenomic analysis with 84 genes of 19 phototrophic euglenoids and 18 cpGenome sequences from Chlorophyta and Streptophyta resulted in a well‐supported cpGenome phylogeny, which is in accordance to former phylogenetic analyses.     

MORPHOLOGICAL SEPARATION OF THE EUGLENOID GENERA TRACHELOMONAS AND STROMBOMONAS (EUGLENOPHYTA) BASED ON LORICA DEVELOPMENT AND POSTERIOR STRIP REDUCTION1

Since the separation of the Trachelomonas Ehrenberg subgroup “Saccatae” into a new genus, Strombomonas Deflandre (1930) , there has been some question as to its validity. Deflandre's separation was based entirely on characteristics of the lorica, including the shape of the lorica, the lack of a distinctive collar, possession of a tailpiece, lack of ornamentation, and the ability of Strombomonas species to aggregate particles on the surface of the lorica. Recent molecular analyses indicated that the loricate taxa (Trachelomonas and Strombomonas) formed a single monophyletic clade; however, the phylogenetic relationship of Strombomonas to Trachelomonas remains unclear because only two Strombomonas taxa have been sequenced to date. In this study, we evaluated the monophyly of the loricate genera using two sets of morphological characters, lorica development and pellicle strip reduction. Lorica development in Strombomonas occurred from the anterior of the cell to the posterior, forming a shroud over the protoplast. In Trachelomonas, a layer of mucilage was excreted over the entire protoplast, followed by creation of the collar at the anterior end. Taxa from both genera underwent exponential strip reduction at the anterior and posterior poles. In Strombomonas only one reduction was visible in the anterior pole, whereas in most Trachelomonas species two reductions were visible. Likewise, Strombomonas species possessed two whorls of strip reduction in the posterior end compared with a single whorl of strip reduction in Trachelomonas species. These morphological characters support the separation of Trachelomonas and Strombomonas as distinct genera.     

12 Phylogeny of the euglenoid loricate genera trachelomonas and strombomonas based on morphological and molecular data

Since the separation of the Trachelomonas subgroup “Saccatae” into a new genus, Strombomonas Deflandre (1930), there has been some question as to its validity. Deflandre's separation was based on morphological characteristics such as the shape of the lorica, lack of a distinctive collar, possession of a tailpiece, lack of ornamentation, and ability to aggregate particles on the lorica. Recent molecular analyses indicated that the loricate taxa were monophyletic, but few species have been sampled. The LSU rDNA from eleven Strombomonas and thirty‐eight Trachelomonas species was sequenced to evaluate the monophyly of the two genera. Bayesian and maximum‐likelihood analyses found one monophyletic clade for each genus. The Trachelomonas clade was weakly supported, but had five strongly supported subclades. Morphological characters, such as lorica development and pellicle strip reduction, also supported separation of the genera. Lorica development in Strombomonas occurred from the anterior of the cell to the posterior, forming a shroud over the protoplast whereas in Trachelomonas, a layer of mucilage was excreted over the entire protoplast, followed by creation of the collar at the anterior end. Taxa from both genera underwent exponential strip reduction at the anterior and posterior poles. In Strombomonas, only one reduction was visible in the anterior pole, while in most Trachelomonas species, two reductions were visible. Likewise, Strombomonas species possessed two whorls of strip reduction in their posterior end compared to a single whorl of strip reduction in Trachelomonas species. The combined morphological and molecular data support the retention of Trachelomonas and Strombomonas as separate genera.     

Electron microscopy of the cell envelope of Ferrobacillus ferrooxidans prepared by freeze-etching and chemical fixation techniques

Remsen, C. C. (Swiss Federation Institute of Technology, Zurich, Switzerland), and D. G. Lundgren. Electron microscopy of the cell envelope of Ferrobacillus ferrooxidans prepared by freeze-etching and chemical fixation techniques. J. Bacteriol. 92:1765-1771. 1966.-A comparison was made of the fine structure of the cell envelope of the gram-negative bacterium Ferrobacillus ferrooxidans when cells were prepared for microscopy by freeze-etching and chemical fixation techniques. Cell envelopes of chemically fixed cells appeared as five separate layers distinguishable by their location and electron density. Frozen-etched cells showed a three-layered complex with each layer measuring approximately 100 A in thickness. The latter technique is considered to be "artifact-free" and, as a technique, yields purely morphological information on the natural state. The three layers revealed by freeze-etching are: the outer layer, a lipoprotein-lipopolysaccharide layer; the middle layer, a layer composed of globular protein attached to fibrillar mucopeptide; and the innermost layer, the cytoplasmic membrane. The latter was covered with 100 to 120 A particles. The relationship of the aforementioned layers to those seen in chemically fixed cells is discussed.     

On the morphology and ultrastructure of the cell wall of Spirulina platensis

The cell wall of the blue-green alga Spirulina platensis was studied with the electron microscope using ultra-thin sectioning, shadowing, carbon-replication or freeze-etching techniques for specimen preparation. The cell wall could be resolved into four layers, L-I through L-IV. The L-I and L-III layers contain fibrillar material. The septum is a three-layered wall: an L-II layer sandwiched between L-I layers. The shape in vitro of isolated septa might be an artifact due to the preparation technique used. Certain structural properties of the septum seem to allow tangential stretching; they might be reflected in the flexible gliding mobility of Spirulina species. The outer, L-IV layer contains material longitudinally arranged along the trichome axis.     

Structure of the extraembryonic matrices around the benthic embryos of Patiriella exigua (Asteroidea) and their roles in benthic development: Comparison with the planktonic embryos of Patiriella regularis

The extracellular matrices (ECMs) surrounding the benthic embryos and larvae of the seastar Patiriella exigua and the planktonic embryos of Patiriella regularis were examined by transmission and scanning electron microscopy. Three ECMs surround unhatched embryos: An outer jelly coat, a fertilization envelope, and an inner hyaline layer. The ECMs of P. exigua are modified for supporting benthic development. The dense jelly coat attaches the embryo to the substratum, and the fertilization envelope forms a though protective case. In comparison, P. regularis has a less dense jelly coat and a thinner fertilization envelope. The hyaline layer of both species is comprised of three main regions: An intervillous layer overlying the epithelium, a supporting layer, and a coarse meshwork layer. Unhatched P. exigua have an additional outer amorphous layer that adheres to the fertilization envelope. As a result, the hyaline layer forms a continuous ECM that unites the embryonic surface with the fertilization envelope. Embryos of P. exigua removed from their fertilization envelopes lack the outer amorphous region, have a poorly developed hyaline layer, and do not develop beyond gastrulation. It appears that the substantial hyaline layer of P. exigua and its attachment to the fertilization envelope are essential for early development and that this ECM may function as a gelatinous cushioning layer around the benthic embryos. At hatching, the amorphous layer is discarded with the envelope. In contrast, an amorphous layer is absent from the hyaline layer of P. regularis. The demembranated embryos of this species have an ECM similar to that of controls and develop normally to the larval stage. © 1995 Wiley-Liss, Inc.     

Extracellular coats on the surface of Strongylocentrotus purpuratus eggs: stereo electron microscopy of quick-frozen and deep-etched specimens

Summary Sea urchin (Strongylocentrotus purpuratus) eggs were fixed, quick-frozen, deep-etched, and rotary-replicated, and the three-dimensional structure of the external surface of the egg visualized using stereo electron microscopy. The cell surface is coated with three layers of filaments: the sheetlike vitelline layer adhering closely to the plasma membrane, a second layer of oblique fibrils extending from microvillar tips to the vitelline layer below, and a third, outermost layer of horizontal filaments coursing in bundles over the microvillar tips. After fertilization, the newly elevated vitelline envelope is transformed into a three-layered structure, the central layer being a tightly knit network of fine filaments decorated on each side with a loose network of thicker fibrils. Subsequently, the envelope becomes coated with paracrystalline protein released from the cortical granules, and microvillar casts are reshaped into angular, jagged peaks having two to five sides. The final structure of the fertilization envelope consists of a thick central layer of compact fibrillar material that is coated on each side with thin plates of paracrystalline protein.     

Comparative buccal anatomy in Helisoma (mollusca,pulmonata, basommatophora)

Dissections were performed to document buccal anatomy in three species of the pulmonate genus Helisoma Swainson, 1840. The 28 muscles which are responsible for radular feeding in these animals are organized in three concentric and integrated envelopes. The deepest of these includes muscles which manipulate the radula about the odontophoral cartilage. Elements of the middle envelope direct movements of the cartilage within the buccal cavity, and muscles of the outer envelope control movements of the buccal mass within the cephalic haemocoel. Motion analysis by videomicrography showed that muscles of the middle and outer envelopes contribute to the action of radular feeding by acting as antagonists to other muscles and to hydrostatic elements of the buccal apparatus. Observations of radular dentition showed that although each of the three species examined has a unique radula, especially with regard to the specific details of tooth shape, all resemble a radula characteristic of the Planorbidae with regard to other, more general, aspects of ribbon architecture.     

PHYLOGENY OF THE EUGLENOID LORICATE GENERA TRACHELOMONAS AND STROMBOMONAS (EUGLENOPHYTA) INFERRED FROM NUCLEAR SSU AND LSU rDNA1

Previous studies using the nuclear SSU rDNA and partial LSU rDNA have demonstrated that the euglenoid loricate taxa form a monophyletic clade within the photosynthetic euglenoid lineage. It was unclear, however, whether the loricate genera Trachelomonas and Strombomonas were monophyletic. In order to determine the relationships among the loricate taxa, SSU and LSU nuclear rDNA sequences were obtained for eight Strombomonas and 25 Trachelomonas strains and combined in a multigene phylogenetic analysis. Conserved regions of the aligned data set were used to generate maximum‐likelihood (ML) and Bayesian phylogenies. Both methods recovered a strongly supported monophyletic loricate clade with Strombomonas and Trachelomonas species separated into two sister clades. Taxa in the genus Strombomonas sorted into three subclades. Within the genus Trachelomonas, five strongly supported subclades were recovered in all analyses. Key morphological features could be attributed to each of the subclades, with the major separation being that all of the spine‐bearing taxa were located in two sister subclades, while the more rounded, spineless taxa formed the remaining three subclades. The separation of genera and subclades was supported by 42 distinct molecular signatures (33 in Trachelomonas and nine in Strombomonas). The morphological and molecular data supported the retention of Trachelomonas and Strombomonas as separate loricate genera.     

Egg-shells in mites

Summary This communication presents results of studies on the formation and structure of the vitelline envelopes in three species of mites: Euryparasitus emarginatus (Gamasida), Erythraeus phalangoides (Actinedida), and Hafenrefferia gilvipes (Oribatida). In E. emarginatus and E. phalangoides, in which the oocytes are not covered with follicular cells, the material of the vitelline envelope appears first in vesicles under the surface of the oocytes prior to secretion by exocytosis. The formed vitelline envelope is built of a homogeneous material which is perforated by numerous channels containing oocyte microvilli. Later, as the microvilli are retracted, the channels disappear. In both of these species the formed vitelline envelope is incomplete and the micropylar orifice occurs as a transitional structure.In H. gilvipes follicular cells encircling the oocyte contain granules filled with material that is subsequently secreted into the perivitelline space forming the vitelline envelope on the oocyte surface. The inner layer of the vitelline envelope is granular, whereas the outer part is more homogeneous. Both lack channels containing microvilli and micropyle.     

Previtellogenic and vitellogenic oocytes in ovarian follicles of cultured siberian sturgeon Acipenser baerii (Chondrostei,Acipenseriformes)

Previtellogenic and vitellogenic oocytes in ovarian follicles from cultured Siberian sturgeon Acipenser baerii were examined. In previtellogenic oocytes, granular and homogeneous zones in the cytoplasm (the ooplasm) are distinguished. Material of nuclear origin, rough endoplasmic reticulum, Golgi complexes, complexes of mitochondria with cement and round bodies are numerous in the granular ooplasm. In vitellogenic oocytes, the ooplasm comprises three zones: perinuclear area, endoplasm and periplasm. The endoplasm contains yolk platelets, lipid droplets, and aggregations of mitochondria and granules immersed in amorphous material. In the nucleoplasm, lampbrush chromosomes, nucleoli, and two types of nuclear bodies are present. The first type of nuclear bodies is initially composed of fibrillar threads only. Their ultrastructure subsequently changes and they contain threads and medium electron dense material. The second type of nuclear bodies is only composed of electron dense particles. All nuclear bodies impregnate with silver, stain with propidium iodide, and are DAPI‐negative. Their possible role is discussed. All oocytes are surrounded by follicular cells and a basal lamina which is covered by thecal cells. Egg envelopes are not present in previtellogenic oocytes. In vitellogenic oocytes, the plasma membrane (the oolemma) is covered by three envelopes: vitelline envelope, chorion, and extrachorion. Vitelline envelope comprises four sublayers: filamentous layer, trabecular layer 2 (t2), homogeneous layer, and trabecular layer 1 (t1). In the chorion, porous layer 1 and porous layer 2 are distinguished in most voluminous examined oocytes. Three micropylar cells that are necessary for the formation of micropyles are present between follicular cells at the animal hemisphere. J. Morphol. 278:50–61, 2017. ©© 2016 Wiley Periodicals,Inc.     

A taxonomic and ultrastructural study of Trachelomonas Ehr. (Euglenophyta) from subtropical Argentina

Fifty-four loricated euglenophyta taxa sampled in the province of Chaco, Argentina, belonging to the genus Trachelomonas Ehr., have been examined by means of scanning electron microscopy. On the basis of these observations three new varieties are proposed: T. oviformis van duplex, T. robusta var. sparsiornata and T. Sydneyensis var. acuminata. Several details of the lorica ultrastructure are illustrated.     

ORGANIZATION AND ACTIVITY IN THE PRE- AND POSTOVULATORY FOLLICLE OF NECTURUS MACULOSUS

The established follicle envelope of Necturus maculosus consists of a layer of follicle cells (granulosa) surrounding the developing oocyte, a layer of theca comprised of connective tissue cells, fibers, and matrix, and a layer of serosal cells. The changes in shape and fine structure of these layers during differentiation accompanying oogenesis are described. The cells and capillaries of the follicle envelope are engaged in an extensive pinocytotic activity, the details of which are described. We used cytochemical techniques to analyze the activity of the follicle envelope with respect to lipid accumulation and alkaline phosphatase activity. Radioautographic results indicate that cells of the follicle envelope are capable of incorporating tritium-labeled uridine and amino acids at certain times during oocyte growth. A comparative analysis was made of the soluble proteins in follicle envelopes isolated from immature oocytes and of those in follicle envelopes isolated from nearly mature oocytes and in postovulatory follicles. After the oocyte is ovulated, the cells of the follicle envelope are converted into a postovulatory follicle. The cells of the postovulatory follicle undergo further differentiation resulting in their becoming actively engaged in the formation of a secretion, the details of which are described at the electron microscope level. Analysis of the postovulatory follicle by thin-layer chromatography and cytochemistry demonstrated the presence of a wide variety of lipid substances and the possible presence of steroid. That the postovulatory follicle may be engaged in steroid biosynthesis is also suggested by studies involving the demonstration of 3 β-hydroxysteroid dehydrogenase activity with cytochemical techniques applied to frozen sections and to soluble proteins separated by gel electrophoresis.     

Egg envelopes of Baetis rhodani and Cloeon dipterum (Ephemeroptera, Baetidae): a comparative analysis between an oviparous and an ovoviviparous species

A comparative ultrastructural investigation on the eggshell (vitelline and chorionic envelopes) has been carried out in the nymphs of two mayfly species encompassed into the Baetidae, namely Baetis rhodani and Cloeon dipterum. During oocyte differentiation in the meroistic telotrophic ovarioles, gametes are connected to discrete nurse cells by trophic cords. In B. rhodani, each ovariole contains several eggs arranged in sequence, whereas in C. dipterum each contains a single egg. Follicle cells are competent for vitelline and chorionic envelope synthesis. Baetis rhodani is an oviparous species and the chorion is fairly thick, formed by an alveolate endochorion and a fibrillar exochorion delimited by a honey‐comb roof. Cloeon dipterum stands out among Ephemeroptera for being ovoviviparous. In B. rhodani, ovulation starts in the older nymphs with dark wing‐pads, whereas in C. dipterum choriogenesis ends in the imaginal stage. Here the chorion is very thin and laid eggs hatch almost immediately, allowing the larvulae to move out. The maturation of a single egg per ovariole is synchronized with the achievement of the adult stage. The acquisition of ovoviviparity has led to remarkable changes in the ovariole organization along with a simplification of the eggshell structure.     

Nature of the salt dependence of the envelope of a Dead Sea archaebacterium,Haloferax volcanii

The external layer was released from Haloferax volcanii cells and envelopes when the divalent cation concentration was lowered in the presence of NaCl. NaCl alone could not stabilize the isolated envelopes and divalent cations were absolutely required at concentrations which depended on that of NaCl and on the temperature. NaCl and divalent cations had a cooperative or an antagonistic effect according to their relative concentrations. The envelopes were optimally stabilized by a combination of NaCl and divalent cations, which probably ensured an equilibrium between the hydrophobic bonds and the charge shielding effects involved in the structure of cell envelope (cytoplasmic membrane and external layer).Deceased 1990     

The fine structure of akinete formation and germination in Cylindrospermum

Summary Akinete formation and germination were studied in a species of Cylindrospermum using the electron microscope. The differentiation of a vegetative cell into an akinete is characterized by cell enlargement, sheath condensation, deposition of several spore envelope layers, including a dense fibrillar layer and deposition of large cyanophycin granules. The mature akinete in addition to the multilayered envelope retains internally a large number of cyanophycin granules, a photosynthetic thylakoid system, polyhedral bodies, lipid deposits and nucleoplasmic regions. Germination of the akinete can take place in several modes differing in detail. Most frequently the spore envelope remains intact and the germling which may or may not have divided emerges through a pore at one end of the envelope. The photosynthetic thylakoid system appears to increase by the fusion of small vesicles found in the cytoplasm. Alpha-granules are numerous and cyanophycin is nearly absent in the germling.     

Fine structure and formation of eggshells in marine Gastrotricha

Summary The fine structure of the gastrotrich eggshell in the hermaphroditic species Turbanella ocellata (Hummon 1974) and the parthenogenetic species Aspidiophorus sp. is described using transmission electron microscopy. The presented evidence strongly suggests that the shell is produced by the egg itself prior to oviposition in both species. The layed egg in Aspidiophorus sp. is provided with a special attachment stalk that is also preformed in the mother animal. Freshly layed eggs of T. ocellata are adhesive all around their surface and lack any specialized structures for attachment. Formation of the spiny eggshell of Aspidiophorus sp. appears to begin with a sudden release of special vesicles containing the preformed spines of the outer eggshell covering. Additional material appears to be secreted by the egg in a more gradual process after the initial vesicle release. The formation of the two fibrous layers in the eggshell of T. ocellata is less well understood and deposition of eggshell material could be seen either as a continuous process or as two separate steps, similar to the events observed for Aspidiophorus sp. For T. ocellata, Tetranchyroderma sp. and Aspidiophorus sp. it is demonstrated that formation of the cuticle occurs as an independent process from that of eggshell formation. This is significantly different from the basic mode of cuticle formation in the annelid line of evolution. The paper argues further that the data support earlier claims of a pronounced difference between the Gastrotricha-Macrodasyida and the Gastrotricha-Paucitubulatina and agree well with the postulated ties of the Gastrotricha and Nematoda. The phylogenetic importance of the eggshell fine-structure is discussed in the framework of present theories on aschelminth phylogeny.Abbreviations cus cuticular spines - cut cuticle - cov coated vesicles - cv cup-shaped vesicles - dp dense particles - ep epidermis - emb embryo - erl lacunae of smooth ER - fgb fibrous and granular bodies - fl fibrous layer - ga Golgi apparatus - gc gut cell - gv Golgi vesicles - im intercellular matrix - isp intercellular space - isl inner shell layer - ld lipid droplet - mdb medium-dense bodies - mvb multivesicular bodies - oc oocyte - od oviduct - osl outer shell layer - o egg - sv spiny vesicles - sh eggshell - st egg-stalk - sl spiny layer - sub substrate - trm trilaminate membrane - yb yolk bodies - yg yolk granule - yoc young oocyte This work was supported by NSF Grant # GB-42211 to R.M. Rieger     

PHYLOGENY OF THE EUGLENALES BASED UPON COMBINED SSU AND LSU RDNA SEQUENCE COMPARISONS AND DESCRIPTION OF DISCOPLASTIS GEN. NOV. (EUGLENOPHYTA)1

A Bayesian analysis, utilizing a combined data set developed from the small subunit (SSU) and large subunit (LSU) rDNA gene sequences, was used to resolve relationships and clarify generic boundaries among 84 strains of plastid‐containing euglenophytes representing 11 genera. The analysis produced a tree with three major clades: a Phacus and Lepocinlis clade, a Discoplastis clade, and a Euglena, Colacium, Trachelomonas, Strombomonas, Monomorphina, and Cryptoglena clade. The majority of the species in the genus Euglena formed a well‐supported clade, but two species formed a separate clade near the base of the tree. A new genus, Discoplastis, was erected to accommodate these taxa, thus making the genus Euglena monophyletic. The analysis also supported the monophyly of Colacium, Trachelomonas, Strombomonas, Monomorphina, and Cryptoglena, which formed two subclades sister to the Euglena clade. Colacium, Trachelomonas, and Strombomonas, all of which produce copious amounts of mucilage to form loricas or mucilaginous stalks, formed a well‐supported lineage. Our analysis supported retaining Strombomonas and Trachelomonas as separate genera. Monomorphina and Cryptoglena formed two well‐supported clades that were sister to the Colacium, Trachelomonas, and Strombomonas clade. Phacus and Lepocinclis, both of which have numerous small discoid chloroplasts without pyrenoids and lack peristaltic euglenoid movement (metaboly), formed a well‐supported monophyletic lineage that was sister to the larger Euglena through Cryptoglena containing clade. This study demonstrated that increased taxon sampling, multiple genes, and combined data sets provided increased support for internal nodes on the euglenoid phylogenetic tree and resolved relationships among the major genera in the photosynthetic euglenoid lineage.     

Study of envelope proteins in E. coli cet and recA mutants by SDS acrylamide gel electrophoresis

Disc-electrophoresis of E. coli envelope proteins on SDS acrylamide gels reproducibly revealed up to 50 distinct polypeptide bands. Corresponding molecular weights ranged from 105,000 to 20,000 daltons or less. Major bands corresponded to molecular weights of 73,000, 48,000, 36,000 and 30,000 with the latter constituting up to 20% of the total envelope protein depending upon the method of isolation. Minimum levels of detection using stained gels equaled 0.25 μg protein or 1% of total sample analyzed; for a polypeptide of molecular weight 40,000 daltons this was calculated to be equivalent to 1,200 molecules per cell envelope. In envelopes from a cetB^? mutant strain (refractory to colicin E2), an additional band, constituting up to 5% of the total envelope protein was present. The molecular weight of this protein, which was maximally present in wild type envelopes in only trace amounts, is 44,000 daltons, indicating a cellular concentration of approximately 6 × 10³ molecules per envelope. This new band was not affected by heating envelope preparations to 100° prior to electrophoresis, but was largely eliminated by washing isolated envelopes in low ionic strength buffer, or by pre-incubating cells with trypsin prior to preparation of envelopes. Treatment of isolated envelopes with Triton X-100, which preferentially releases inner membrane proteins from the envelope (18), resulted in the extraction of a preponderance of the high molecular weight polypeptides, including the 44,000 dalton protein from envelopes of the mutant. The major polypeptides of the envelope and the low molecular weight components were not extracted by Triton X-100. The properties of the 44,000 dalton protein indicated that it is relatively loosely associated with the surface envelope and may be exposed on the external surface of the cytoplasmic membrane. Possible explanations for the appearance of this protein in mutant strains and its relationship to the inability of these to respond, specifically to surface bound colicin E2, will be discussed. Extensive analysis of envelopes from recA^? mutants was also carried out and revealed an unusual amount of variation in polypeptide profiles obtained from different preparations. However, no consistent quantitative or qualitative difference between recA and rec⁺ strains was obtained. In recA, cetB double mutants, the increased level of the 44,000 dalton polypeptide was identical to that found in the rec⁺, cetB mutant.     

Light and electron microscopic study of <Emphasis Type="Italic">Pelomyxa flava sp.n.</Emphasis> (archamoebae,pelobiontida)

The morphology of a new species of pelobionts Pelomyxa flava was studied by light and electron microscopy. The envelopes of P. flava are consist of a plasma membrane with a thick layer of weakly structured glycocalyx on its outer surface. Numerous flagella are often located at the apices of short conical pseudopodia. Kinetosomes of flagella reach length of 0.9 μm and are hollow with a pronounced central filament. The rootlet system is represented by three groups of microtubules: the radial, basal, and the microtubules of lateral root. The transitory zone is short and does not reach beyond the level of the cell surface; the axoneme is characterized by an unstable set of microtubules. Trophic stages of the P. flava life cycle are represented by binuclear cells; plasmotomy is performed at the tetranuclear stage. Nuclei have a granular structure. Fibrillar nuclear bodies are revealed in the karyoplasm. The nuclear envelope has a complex organization; on its surface, the outer membrane has a layer of electron-dense material that contacts with short microtubules located single-row at the surface of the nuclear envelope. Vesicles and cisterns of endoplasmic reticulum are located away from microtubules and are derivatives of the nuclear envelope. In the P. flava endoplasm, the presence of structural and digestive vacuoles and glycogen granules was found. Three types of prokaryotic cytobionts were revealed. Large multimembranous organelles reaching 5 μm in diameter were described for the first time. Peculiarities of the morphology and biology of P. flava compared to the previously studied Pelomyxa species are discussed.