O. I. Baulina

Zavarzinella formosa gen. nov., sp. nov., a Novel Stalked, Gemmata-like Planctomycete from a Siberian Peat Bog

An aerobic, pink-pigmented, budding and rosette-forming bacterium was isolated from an acidic Sphagnum peat bog and designated strain A10(T). The 16S rRNA gene sequence analysis showed that strain A10(T) was a member of the order Planctomycetales and belonged to a phylogenetic lineage defined by the genus Gemmata, with 90 % sequence similarity to that of Gemmata obscuriglobus, the only taxonomically described organism of this group. Ellipsoid-shaped cells of strain A10(T) were uniformly covered with crateriform pits and possessed long (up to 10-15 mum) and unusually thick (0.5-0.7 mum) stalks of a unique ultrastructure. Thin sections revealed a complex intracellular membrane system compartmentalizing the cells. Strain A10(T) was a moderately acidophilic, mesophilic organism capable of growth at pH values between 3.8 and 7.2 (with an optimum at pH 5.5-6.0) and at temperatures between 10 and 30 degrees C (with an optimum at 20-25 degrees C). The major fatty acids were C(18 : 0), C(18 : 1)omega5c and C(16 : 1)omega5c and the major quinone was MK-6. Cells of strain A10(T) contained high amounts of bound saturated and monounsaturated C(26)-C(32) (omega-1) hydroxy fatty acids. The G+C content of the DNA was 62.5 mol%. The unique cell morphology, the capability of growth in acidic conditions and a number of chemotaxonomic and genotypic characteristics served to differentiate strain A10(T) from G. obscuriglobus. Based on these data, the novel isolate should be considered as representing a novel genus and species of planctomycetes, for which the name Zavarzinella formosa gen. nov., sp. nov. is proposed The type strain is A10(T) (=DSM 19928(T)=VKM B-2478(T)).

Oscillochloris trichoides neotype strain DG-6

The new strain of filamentous green bacterium strain DG-6 was isolated in pure culture from the spring of Caucuses. The study of this bacterium allows to suggest that it is a member of the familyChloroflexaceae and may be considered asOscillochloris trichoides neotype strain. The description of this green bacterium is given.

Artificial Cyanobacterium-Plant Symbioses

Studies conducted during the last decade have significantly improved our knowledge of the differrent stages in formation and function of artificial associations involving cyanobacteria and furnished new data on the involvement of satellite bacteria in this process. The strenuous efforts to create artificial associations between important agricultural plants and nitrogen-fixing microorganisms have yielded promising results particularly for introducing heterocyst-forming cyanobacteria into the plant rhizosphere. Important progress has also been made in the induction of root paranodule and colonization of such para-nodules by microsymbionts.

Associations between the White Sea Invertebrates and Oxygen-Evolving Phototrophic Microorganisms

Eleven species of White Sea invertebrates (sponges, actinians, hydroids, polychaetes, and nudibranch mollusks) were tested for the presence of associated oxygen-evolving phototrophic microorganisms (OPM) (microalgae and cyanobacteria). Two main approaches were applied: (a) light and electron microscopy of intact samples and fixed preparations of invertebrates, and (b) isolation of microorganisms from samples of invertebrates after mild surface sterilization. The obtained results lead to conclusions on the formation of multicomponent associations by White Sea invertebrates and OPM based on the following data: (1) isolation of 27 cultures of OPM from eight species of invertebrates (sponges, hydroids, polychaete trochophore larva), (2) specificity of association between epibiontic communities of microorganisms and macroorganisms within the same biotope, and (3) spatial integration of micro- and macropartners resulting in the formation of morphological structures within the interorganismic contact zones.

Similarity and diversity of the Desmodesmus spp. microalgae isolated from associations with White Sea invertebrates.

Similarity and diversity of the phenotype and nucleotide sequences of certain genome loci among the single-celled microalgae isolated from White Sea benthic invertebrates were studied to extend the knowledge of oxygenic photoautotrophs forming microbial communities associated with animals. We compared four Desmodesmus isolates (1Hp86E-2, 1Pm66B, 3Dp86E-1, 2Cl66E) from the sponge Halichondria panicea, trochophore larvae of the polychaete Phyllodoce maculata, and the hydroids Dynamena pumila and Coryne lovenii, respectively. The microalgae appeared to be very similar featuring the phenotypic and genetic traits characteristics of unicellular representatives of the genus Desmodesmus. At the same time, isolates from different animal species displayed certain differences in (i) the epistructure morphology; (ii) type and number of the inclusions such as interthylakoid starch grains and cytoplasmic oil bodies and (iii) fatty acid composition; in Desmodesmus sp. 1Hp86E-2, these differences were most pronounced. Phylogenetic analysis based on ITS1-5.8S rRNA-ITS2 and rbcL sequences showed that all isolates studied differ from known classified representatives of Desmodesmus combining a deletion in the conservative 5.8S rRNA gene and long AC-microsatellite repeats in the ITS1 whereas 1Hp86E-2 represented a distinct branch within this group.

Green microalgae isolated from associations with white sea invertebrates

Endophotosymbionts (cyanobacteria, microalgae, or their functionally active chloroplasts) were found in mollusks, sponges, corals, anemones, freshwater hydra, worms, and ascidians [1–2]. Associations of colonial hydroids with epibiotic microalgae and cyanobacteria were previously described [3 ⎯5]. It is known that isolation of animal microsymbionts is sel� dom successful. The information on the isolation of phototrophic microrganisms associated with inverte� brates of the high latitude seas, especially the White Sea, is limited and mainly refers to cyanobacteria [4]. The goal of the present work was to study the microalgae isolated from associations with the White Sea invertebrates and to characterize their morphol� ogy, ultrastructure, and the composition of pigments and fatty acids. Microalgae analyzed in the study were isolated from the benthic animals collected in the region of the Moscow State University White Sea Biological Station ( 66°34′N, 33°08′E) in the Kandalaksha Bay of the White Sea. Microalgae were isolated from the inverte� brates with green zones containing red autolumines� cent bodies within their tissues or covers. Isolation and microscopy were carried out as described [4, 5]. Fatty acid and pigment analysis was carried out according to the method in [6]; molecular genetic analysis was car� ried out as described in [7].

Ultrastructure of cyanobacterium Nostoc sp. f. Blasia cell forms in persisting populations

Cell clusters formed in persistent populations of Nostoc sp. f. Blasia, a cyanobacterium capable of cell differentiation, under prolonged storage in the dark at low temperatures were studied for the first time. Cell reorganization was observed, including changes in the ultrastructure of thylakoids, the cell wall peptidoglycan layer, and carboxysomes. Subcellular structures involved in intercellular communication within the clusters were revealed (structures similar to microplasmodesms and contact pores, secretory vesicles, etc.) Persistence of cyanobacterial populations was concluded to result from formation not only of specialized dormant cells (akinetes), but also L-forms, as well as from the modification changes of the clustered vegetative cells. A cluster containing the vegetative cells and L-like forms within a common intercellular matrix is considered a structural unit at the supracellular level, which is responsible for survival of cyanobacterial populations when mass akinete formation does not occur.

Atypical Cell Forms Overproducing Extracellular Substances in Populations of Cycad Cyanobionts

The ultrastructure of the cyanobionts of the greenhouse-grown cycads Cycas circinalis, Ceratozamia mexicana, and Encephalartos villosus was studied. The cyanobiont microcolonies grown in the intercellular space of the cyanobacterial zone of cortical parenchyma in the cycad coralloid roots contained two specific forms of vegetative cells with a reduced cell wall, namely, protoplasts and spheroplasts. The protoplasts and spheroplasts exhibited ultrastructural properties indicating the overproduction of two extracellular substances, one of which resembled the mucilage polysaccharides and the other was protein-like. The substances were likely to be synthesized intracellularly and then be excreted with the aid of surface vesicles or by ruptures in the cytoplasmic membrane to form, respectively, a mucilagious extracellular matrix and an additional electron-opaque envelope around the cell. At the late developmental stages, the excretion of these substances was accompanied by degradative changes in the cells, leading eventually to cell death. The physiological role of these specific cell forms and the factors that induce their development and death in the cell populations of cyanobionts are discussed.

Versatility of the green microalga cell vacuole function as revealed by analytical transmission electron microscopy

Vacuole is a multifunctional compartment central to a large number of functions (storage, catabolism, maintenance of the cell homeostasis) in oxygenic phototrophs including microalgae. Still, microalgal cell vacuole is much less studied than that of higher plants although knowledge of the vacuolar structure and function is essential for understanding physiology of nutrition and stress tolerance of microalgae. Here, we combined the advanced analytical and conventional transmission electron microscopy methods to obtain semi-quantitative, spatially resolved at the subcellular level information on elemental composition of the cell vacuoles in several free-living and symbiotic chlorophytes. We obtained a detailed record of the changes in cell and vacuolar ultrastructure in response to environmental stimuli under diverse conditions. We suggested that the vacuolar inclusions could be divided into responsible for storage of phosphorus (mainly in form of polyphosphate) and those accommodating non-protein nitrogen (presumably polyamine) reserves, respectively.The ultrastructural findings, together with the data on elemental composition of different cell compartments, allowed us to speculate on the role of the vacuolar membrane in the biosynthesis and sequestration of polyphosphate. We also describe the ultrastructural evidence of possible involvement of the tonoplast in the membrane lipid turnover and exchange of energy and metabolites between chloroplasts and mitochondria. These processes might play a significant role in acclimation in different stresses including nitrogen starvation and extremely high level of CO2 and might also be of importance for microalgal biotechnology. Advantages and limitations of application of analytical electron microscopy to biosamples such as microalgal cells are discussed.

Physiological plasticity of symbiotic Desmodesmus (Chlorophyceae) isolated from taxonomically distant white sea invertibrates

The physiological heterogeneity of closely related symbiotic microalgae from taxonomically distant animal hosts was studied for the first time. Three strains of unicellular algae from the genus Desmodesmus (Chlorophyceae) isolated from White Sea benthic invertebrates were used as the object in this study. The effects of nitrogen starvation and high light intensity on the growth, changes in chlorophyll and total carotenoid contents and fatty acid content and composition of the microalgal cell lipids were followed. Nitrogen starvation declined the biomass accumulation rate as well as chlorophyll and carotenoid contents on the background of the enhanced fatty acid accumulation in all strains studied. The ultrastructural study revealed the reduction of photosynthetic apparatus and an increase in the proportion of cell volume occupied by oil bodies and starch grains as well as an increase in the cell wall thickness. A decline in the effective per cell irradiance in the cultures of higher cell density, as a rule, slowed down the changes in pigment and fatty acids composition characteristic of nitrogen starvation. The rates of biomass accumulation and cell biochemical composition under the nitrogen-starvation conditions were strain-specific. In most cases, the decline in chlorophylls proceeded at a higher rate in comparison with that of carotenoid decline. In two of the three strains studied, both these process occurred synchronously with the decline in the unsaturation of the cell lipid fatty acids. The possibilities of biotechnological application of the symbiotic microalgae are discussed with the peculiarities of their stress physiology in mind.