Limnothrix redekei (Van Goor) Meffert (Cyanobacteria) Strains from Lake Kastoria, Greece Form a Separate Phylogenetic Group

Three strains of Limnothrix (Cyanobacteria) isolated from Lake Kastoria, Greece, were characterized based on their morphological features and 16S rRNA gene sequences. The Limnothrix isolates 007a, 165a, and 165c can morphologically be assigned to Limnothrix redekei (Van Goor) Meffert. The 16S rRNA gene of the Limnothrix strains showed a 99% similarity to the 16S rRNA gene of Planktothrix sp. FP1. Limnothrix redekei strains 165a, 165c, 007a and Planktothrix sp. FP1 formed a separate cluster in the cyanobacterial 16S rRNA gene tree. It was distinct from the Pseudanabaena cluster, which included the other Limnothrix strains isolated from northern temperate lakes. This is the first report on the phylogeny of L. redekei strains originating from a Mediterranean lake (southern Europe) and provides new data about the genus Limnothrix.     

Toxic Blue-green Algae Water Blooms Found in some Lakes in the German Democratic Republic

From 1977 to 1979 plankton samples were taken from 6 lakes in the German Democratic Republic (GDR) during water blooms and examined for their toxicity to homothermal animals. Microcystis aeruginosa, Aphanizomenon flos-aquae, Anabaena spiroides, and Oscillatoria redekei were dominant in the samples. With the exception of Oscillatoria redekei the algae tested had toxic effects on mice after intraperitoneal injection. The rate of survival of the test animals was particularly low when the algae were disintegrated by ultrasound or freeze-drying prior to injection, this indicating the endogenic character of the toxins. Water blooms of Microcystis aeruginosa taken from Lake Pehlitzsee (Eberswalde District) showed the highest toxicity with an LD₃₀ as high as 45 and 43.7 mg/kg, respectively. Injection of the lyophilized cells of Aphanizomenon flos-aquae brought about the same symptoms in the test animals as in the case of Microcystis, but the LD₃₀ was 200 mg/kg.     

Competition between the Cyanobacterium Limnothrix redekei and Some Spring Species of Diatoms under P-Limitation

The nutrient saturated growth and the competition between Limnothrix redekei and some spring diatoms for phosphate were studied in semi-continuous cultures at 10°C with a 6/18 h light/dark cycle and at 15 °C with a 12/12 light/dark cycle. Under these conditions in unialgal cultures, the maximum specific growth rate of Limnothrix redekei was two to three time lower than that of the diatoms. However, Limnothrix redekei was the superior competitor for phosphate under both conditions in mixed cultures. The diatoms in mixed cultures from each species with Limnothrix redekei were competitively displaced but at a different rate. This allowed the diatoms to be ranked in terms of their competitive ability for phosphate at 10°C as follows: Synedra acus > Asterionella formosa > Stephanodiscus minutulus > Nitzschia acicularis > Cyclotella meneghiniana > Stephanodiscus neoastrea > Stephanodiscus hantzschii. The competitive ability of Limnothrix redekei at 15 °C was increased and the rank order of diatoms slightly changed. The hypothesis that cyanobacteria are promoted by phosphate because they are inferior competitors for phosphate is incorrect for Limnothrix redekei.     

The influence of daylength,light intensity and temperature on the growth rates of planktonic blue-green algae

The in vitro growth rates under continuous light of the four dominant blue-green algae in Lough Neagh, Anabaena flos-aquae Bréb., Aphanizomenon flos-aquae Ralfs fa. gracile Lemm., Oscillatoria agardhii Gom. and Oscillatoria redekei van Goor were slower than in situ rates from Lough Neagh that had been corrected for hours of light received by the algae. However, by culturing on a 6: 18 light-dark cycle in vitro growth rates were obtained that were similar to the in situ rates. Under continuous light small species showed the fastest growth with Oscillatoria redekei the dominant species. However, this pattern was almost completely reversed under the light-dark cycle with Oscillatoria redekei only exhibiting the fastest growth rate under low light conditions. This observation showed agreement with Lough Neagh field data which showed that Oscillatoria redekei reached its maximum crop in April while the other three species were dominant during the summer months. Compared to the generally assumed high thermal tendency of blue-green algae the temperature maxima of the four species were low. No growth was observed at 35°C for any species while Anabaena flos-aquae was severely inhibited at 25°C.     

Morphology and taxonomy of Oscillatoria redekei (Cyanophyta)

The polymorphous trichome apices of Oscillatoria redekei are described with respect to their shape and size. Breakage of trichomes may occur either trans- or intercellularly. The development and localization of intercellular trichome breakage were observed. Transmission electron microscopy shows that the fine structure of cell walls resembles that of Pseudanabaena galeata. Longitudinal walls consist of three or four layers and lack a sheath, while the cross walls are composed of three layers with a dominating L₂-layer. In contrast to P. galeata, the centroplasm and most of the thylakoidal region of adjacent cells of O. redekei are connected by the cross walls forming obtuse angles at the site of the longitudinal walls. The main characteristics of O. redekei and of Pseudanabaena species are discussed.     

Fatty acids with antibacterial activity from the cyanobacterium Oscillatoria redekei HUB 051

Bioassay-guided fractionation of the n-hexane extract prepared from the biomass of the cyanobacterium Oscillatoria redekei syn. Limnothrix redekei HUB 051 by silica gel and RP-18 column chromatography followed by HPLC resulted in the isolation of a mixture of two unsaturated hydroxy fatty acids. Their further separation using normal phase HPLC resulted in the identification of -dimorphecolic acid, a 9-hydroxy-10E, 12Z-octadecadienoic acid (9-HODE) and of coriolic acid, a 13-hydroxy-9Z, 11E-octadecadienoic acid (13-HODE). In agar plate diffusion test these fatty acids inhibited the growth of the Gram-positive bacteria Bacillus subtilis SBUG 14, Micrococcus flavus SBUG 16 and Staphylococcus aureus SBUG 11 and ATCC 25923, but no activity was observed against multiresistant Staphylococcus aureus strains. This is the first report about antibacterial activity of these hydroxylated unsaturated fatty acids and about the occurrence of coriolic acid in cyanobacteria.     

Density gradient centrifugation (DGC) in Percoll for isolation and characterization of Oscillatoria spp. from Tjeukemeer

SUMMARY.

• 1 A high degree of separation was achieved in isolating Oscillatoria redekei and O. agardhii separately from Tjeukemeer seston by density gradient centrifugation (DGC) in Percoll. When diatoms were abundant, however, a pre-incubation in settling cyhnders was applied to obtain an optimal separation of O. redekei from diatoms.
• 2 One major band dominated by O. redekei was formed in the gradients. O. agardhii showed a varying distribution over three different bands and its banding pattern seemed to be related to the centrifugation resistance of its gas vacuoles and the turgor pressure.
• 3 Pigment ratios of O. agardhii were not affected by DGC in Percoll.

     

POLYPHASIC STUDY OF ANTARCTIC CYANOBACTERIAL STRAINS1

We isolated 59 strains of cyanobacteria from the benthic microbial mats of 23 Antarctic lakes, from five locations in two regions, in order to characterize their morphological and genotypic diversity. On the basis of their morphology, the cyanobacteria were assigned to 12 species that included four Antarctic endemic taxa. Sequences of the ribosomal RNA gene were determined for 56 strains. In general, the strains closely related at the 16S rRNA gene level belonged to the same morphospecies. Nevertheless, divergences were observed concerning the diversity in terms of species richness, novelty, and geographical distribution. For the 56 strains, 21 operational taxonomic units (OTUs, defined as groups of partial 16S rRNA gene sequences with more than 97.5% similarity) were found, including nine novel and three exclusively Antarctic OTUs. Sequences of Petalonema cf. involvens and Chondrocystis sp. were determined for the first time. The internally transcribed spacer (ITS) between the 16S and the 23S rRNA genes was sequenced for 33 strains, and similar groupings were observed with the 16S rRNA gene and the ITS, even when the strains were derived from different lakes and regions. In addition, 48 strains were screened for antimicrobial and cytotoxic activities, and 17 strains were bioactive against the gram‐positive Staphylococcus aureus, or the fungi Aspergillus fumigatus and Cryptococcus neoformans. The bioactivities were not in coincidence with the phylogenetic relationships, but rather were specific to certain strains.     

IN SITU ALLELOPATHIC POTENTIAL OF MYRIOPHYLLUM VERTICILLATUM (HALORAGACEAE) AGAINST SELECTED PHYTOPLANKTON SPECIES1

The potential allelopathic impact of Myriophyllum verticillatum L. under in situ conditions was determined in a series of field and laboratory experiments. Coexistence experiments were performed in a lake dominated by M. verticillatum (Van Goor) Meffert where we exposed three unialgal phytoplankton cultures in dialysis tubes to macrophyte exudates regularly during the vegetated period. Plant content and exudation of polyphenolic compounds were determined, and the inhibitory activity of polyphenol‐containing extracts was tested in bioassays with cyanobacteria. To account for possible resource interference, we monitored growth and photosynthesis of phosphorus‐limited and unlimited cyanobacterium Limnothrix redekei in dialysis tubes exposed to M. verticillatum in aquaria. A high allelopathic potential of M. verticillatum was concluded from high tissue concentrations of total phenolic compounds of 6%–12% of dry matter, the demonstrated release of bioactive polyphenols into the surrounding medium, and the inhibition of cyanobacteria by extracts. We could not unambiguously demonstrate the exudation of polyphenols by M. verticillatum in situ due to interference with allochthonous humic compounds. In laboratory experiments, L. redekei exhibited significantly reduced maximum relative electron transport rates when co‐cultivated in dialysis tubes with M. verticillatum. The field dialysis tube experiment confirmed this result, accompanied by a decline of chl a and PSII activity for L. redekei and the diatom Stephanodiscus minutulus (Kütz.) Greve et Möller, but not for the green alga Scenedesmus armatus Chodat in August. At other times, either no effects or stimulatory effects were observed with all species. Nutrient limitation of the target species may have masked allelopathic effects, and M. verticillatum may have enhanced phytoplankton growth due to phosphorus leakage.     

Application of ribulose-1,5-bisphosphate carboxylase/oxygenase genes as molecular markers for assessment of the diversity of autotrophic microbial communities inhabiting the upper sediment horizons of the saline and soda lakes of the Kulunda Steppe

The genes encoding the key metabolic reactions are often used as functional markers for phylogenetic analysis and microbial ecology studies. The composition and structure of the genes encoding ribulose-1,5-bisphosphate carboxylase (RuBisCO) of various photoautotrophic bacteria, representatives of the order Chromatiales, including collection strains and the strains isolated from saline and soda lakes, were studied in detail. The green-like form I RuBisCO was detected in the majority of the studied strains. In some strains, the genes encoding both form I and form II RuBisCO were present, which has not been previously known for the representatives of this group of bacteria. Moreover, RuBisCO genes were used as functional markers to investigate the autotrophic microbial community inhabiting the upper horizons of bottom sediments of two saline soda lakes and two hypersaline neutral lakes of the Kulunda Steppe. In general, the diversity of autotrophic bacteria in the studied sediment horizons was low. In soda lakes, haloalkaliphilic cyanobacteria and sulfuroxidizing bacteria (SOB) of the genus Halorhodospira were predominant. In saline lakes, halophilic chemoautotrophic SOB Halothiobacillus and Thioalkalivibrio were found, as well as photoautotrophic bacteria of the genus Ectothiorhodosinus and cyanobacteria. Many phylotypes remained unidentified, which indicates the presence of groups of microorganisms with an unknown type of metabolism.     

Gammaproteobacterial Diversity and Carbon Utilization in Response to Salinity in the Lakes on the Qinghai–Tibetan Plateau

The Gammaproteobacteria are widely and abundantly distributed in various environments, and they play important roles in the geochemical cycles of biogenic elements (e.g., C, N and S) in the ecosystems. Previous studies showed that Gammaproteobacteria dominate in saline and hypersaline lakes. However, little is known on how salinity influences gammaproteobacterial community composition and their ecological functions (i.e., organic carbon degradation). In this study, we investigated the gammaproteobacterial diversity and carbon utilization and their response to salinity in six saline/hypersaline lakes and one freshwater lake on the Qinghai–Tibetan Plateau (QTP). The results indicated that the gammaproteobacterial community composition was mainly influenced by the salinity of the studied QTP lakes. Salinity was also a key environmental factor influencing the carbon utilization ability of Gammaproteobacteria: within one genus (e.g., Halomonas, Pseudoalteromonas, Vibrio) the strains retrieved from low-salinity environments had stronger carbon utilization ability than their counterparts from high-salinity environments; within one genus, the strains isolated from lakes with different salinity shared similar carbon utilization preference, indicating that species belonging to the same genus may execute similar ecological functions in the environments regardless of salinity.     

Characterization of morphospecies and strains of the genus Microcystis (Cyanobacteria) for a reconsideration of species classification

For characterization of Microcystis species and strains, cell size, growth temperature optimum, salinity tolerance, dark chemoheterotrophy, photoheterotrophy, guanine + cytosine content in DNA, total fatty acid composition and restriction fragment length polymorphism of a polymerase chain reaction product (PCR-RFLP) of the cpcBA intergenic spacer and flanking region were examined using 24 strains of Microcystis isolated from various lakes and ponds in Japan. From the results obtained it was observed that Microcystis spp. displayed low phenotypic diversity. Cell diameters of these strains were overlapping and there was no clear correlation with morphospecies. Slight differences in growth temperature optimum and salinity tolerance were observed among all strains. No strains showed either chemoheterotrophy or photoheterotrophy. The fatty acids present were the same in different strains although the amounts were different. All the strains had a similar G + C content ranging from 39 to 43 mol%. The phonogram constructed from the PCR-RFLP analysis showed that the species assignment for Microcystis species by morphology did not correspond with the genetic background.     

CILIATE‐SYMBIONT SPECIFICITY OF FRESHWATER ENDOSYMBIOTIC CHLORELLA (TREBOUXIOPHYCEAE,CHLOROPHYTA)1

The nature of Chlorella symbioses in invertebrates and protists has attracted much interest, but the uncertain taxonomy of the algal partner has constrained a deeper ecological understanding of this symbiosis. We sequenced parts of the nuclear 18S rDNA, the internal transcribed spacer (ITS)‐1 region, and the chloroplast 16S rDNA of several Chlorella isolated from pelagic ciliate species of different lakes, Paramecium bursaria symbionts, and free‐living Chlorella to elucidate phylogenetic relationships of Chlorella‐like algae and to assess their host specificity. Sequence analyses resulted in well‐resolved phylogenetic trees providing strong statistical support for a homogenous ‘zoochlorellae’ group of different ciliate species from one lake, but clearly different Chlorella in one of those ciliate species occurring in another lake. The two Chlorella strains isolated from the same ciliate species, but from lakes having a 10‐fold difference in underwater UV transparency, also presented a distinct physiological trait, such as the ability to synthesize UV‐absorbing substances known as mycosporine‐like amino acids (MAAs). Algal symbionts of all P. bursaria strains of different origin resolved in one clade apart from the other ciliate symbionts but split into two distinct lineages, suggesting the existence of a biogeographic pattern. Overall, our results suggest a high degree of species specificity but also hint at the importance of physiological adaptation in symbiotic Chlorella.     

Population dynamics of Limnothrix redekei,Oscillatoria lanceaeformis,Planktothrix agardhii and Pseudanabaena limnetica (cyanobacteria) in a shallow hypertrophic lake (Spain)

Populations of Limnothrix redekei, Oscillatoria lanceaeformis, Planktothrix agardhii and Pseudanabaena limnetica were found in a hypertrophic, gravel-pit lake near Madrid (Spain), throughout a one year sampling at weekly intervals. Physico-chemical factors, phytoplankton biomass and net growth rates were measured. Oscillatoria lanceaeformis was only observed a few weeks, probably being related to phosphorus limitation. Planktothrix agardhii biomass was related to PhAR irradiances, light attenuation coefficient in the water, Brunt-Väisäla frequency and decrease of soluble reactive phosphorus. Limnothrix redekei and Pseudanabaena limnetica biomass values were related to a decrease of inorganic nitrogen and temperature. A different lag response of populations was observed in relation to the environmental features.     

Extremophile Culture Collection from Andean Lakes: Extreme Pristine Environments that Host a Wide Diversity of Microorganisms with Tolerance to UV Radiation

A total of 88 bacterial strains were isolated from six Andean lakes situated at altitudes ranging from 3,400 to 4,600 m above sea level: L. Aparejos (4,200 m), L. Negra (4,400 m), L. Verde (4,460 m), L. Azul (4,400 m), L. Vilama (4,600 m), and Salina Grande (3,400 m). Salinity ranged from 0.4 to 117 ppm. General diversity was determined by denaturing gradient gel electrophoresis (DGGE) analysis. From the excised DGGE bands, 182 bacterial sequences of good quality were obtained. Gammaproteobacteria and Cytophaga/Flavobacterium/Bacteroides (CFB) were the most abundant phylogenetic groups with 42% and 18% of identified bands, respectively. The isolated strains were identified by sequence analysis. Isolated bacteria were subjected to five different UV-B exposure times: 0.5, 3, 6, 12, and 24 h. Afterwards, growth of each isolate was monitored and resistance was classified according to the growth pattern. A wide interspecific variation among the 88 isolates was observed. Medium and highly resistant strains accounted for 43.2% and 28.4% of the isolates, respectively, and only 28.4% was sensitive. Resistance to solar radiation was equally distributed among the isolates from the different lakes regardless of the salinity of the lakes and pigmentation of isolates. Of the highly resistant isolates, 44.5% belonged to gammaproteobacteria, 33.3% to betaproteobacteria, 40% to alphaproteobacteria, 50% to CFB, and among gram-positive organisms, 33.3% were HGC and 44.5% were Firmicutes. Most resistant strains belonged to genera like Exiguobaceterium sp., Acinetobacter sp., Bacillus sp., Micrococcus sp., Pseudomonas sp., Sphyngomonas sp., Staphylococcus sp., and Stenotrophomonas sp. The current study provides further evidence that gammaproteobacteria are the most abundant and the most UV-B-resistant phylogenetic group in Andean lakes and that UV resistance in bacteria isolated from these environments do not depend on pigmentation and tolerance to salinity.     

Planktothrix populations in subalpine lakes: selection for strains with strong gas vesicles as a function of lake depth,morphometry and circulation

1. The genus Planktothrix (Cyanobacteria) usually produces concentrated populations of filaments in the summer metalimnion of thermally stratifying lakes. This has been associated with the action of gas vesicles, cellular structures providing positive buoyancy. At the end of the summer, filaments are carried by convective mixing deeper into the water column where some gas vesicles collapse as a result of high hydrostatic pressure. They then lose their buoyancy, sink and are lost from the euphotic zone. 2. The resistance of gas vesicles to hydrostatic pressures is critical for the survival of Planktothrix in deep lakes. However, comparative observations on populations from lakes of a range of depths and hydrodynamic regimes are still needed to examine the relationships between the adaptive trait (i.e. the ‘critical’ pressure at which each gas vesicle collapses) with the environmental factor (i.e. the maximum hydrostatic pressure). 3. To explore the adaptation of Planktothrix populations to the depth of winter circulation in different systems, we collected 276 strains of P. cf. rubescens from eight lakes (z_max = 24–410 m) in Northern Italy during summer 2009 and we analysed the multicopy gene gvpC coding for a protein that crucially influences the critical pressure. 4. The strains analysed clustered into two main groups having gas vesicles with a mean critical pressure of 1.1 and 0.9 MPa, respectively. The proportion of the stronger strains was generally positively related to lake depth, although the overall pattern was complicated by individual lake morphology and hydrology. The relative frequency of stronger filaments was (i) greatest in deep basins with concave slopes and (ii) least in one deep, but permanently stratified lake. 5. The simultaneous presence of ‘weaker’ and ‘stronger’ filaments could allow for a rapid adaptive response to changes in hydrostatic pressures, related to changes in the amplitude of vertical circulation characterising deep lakes.     

Winter phytoplankton communities in different depths of three mesotrophic lakes (Łęczna-Włodawa Lakeland, Eastern Poland)

Phytoplankton samples were collected from three mesotrophic lakes: Piaseczno, Rogóźno and Krasne during winter seasons (from January to March). The samples were analyzed for species analysis and abundance of planktonic algae in relation to different depths of water column (0–7 m). Selected water physical-chemical parameters were also measured. Abundance of phytoplankton depended strongly on the thickness of snow and ice cover or mixing conditions. The maximal phytoplankton total number reached about 5 × 10⁶ ind. L⁻¹ beneath the clear ice in the Krasne Lake, minimal numbers were recorded under the thick snow and ice layers in the Piaseczno Lake (2 × 10³ ind. L⁻¹). The winter phytoplankton communities were dominated by flagellates principally cryptomonads (Cryptomonas spp. Rhodomonas minuta), euglenophytes (Trachelomonas volvocina, T. volvocinopsis), dinoflagellates (Peridinium bipes, Gymnodinium helveticum) and chrysophytes (Mallomonas elongata, M. akrokomos, Dinobryon sociale) or non-motile small species of blue-green algae (e.g. Rhabdoderma lineare, Limnothrix redekei), diatoms (Stephanodiscus spp., Asterionella formosa), and green algae (e.g. Scenedesmus spp., Monoraphidium spp.). Phytoplankton abundance and structure showed differentiation during the winter season and along the water column as well.     

The genusDaphnia in Cameroon,West Africa

Three species of the genusDaphnia are recorded from Cameroon.Daphnia obtusa was found in a single lake out of 37 sampled.Daphnia laevis was found in the same lake asD. obtusa and in two other lakes, whileD. rosea was found in three other lakes. All the lakes were at altitudes over 1 000 m. The records can be interpreted either as altitudinal survivals of continually dispersing species, or as relicts in an area whereDaphnia is usually very rare or absent.     

Unexpected finding of the "tropical" bacterial pathogen<Emphasis Type="Italic"> Plesiomonas shigelloides</Emphasis> from lake water north of the Polar Circle

The occurrence of Plesiomonas shigelloides in fresh water from six lakes located north of the Polar Circle in the northern part of Sweden was investigated. Bacteriological analysis of the water samples revealed the presence of nine isolates of P. shigelloides from one of the six lakes. All nine isolates were tested for biochemical characterisation, and serological and genomic typing. The biochemical profiles of all nine isolates were identical. Two strains were non-agglutinating for the O and H antigens. The other seven displayed an O19 serotype, whereas H antigen showed non-agglutinating properties. The genotyping results showed that the O19 isolates presented the same pattern, while the two non-agglutinating strains presented patterns that were different to that of the seven others. The results show that P. shigelloides can occur in aquatic environments where the temperature conditions are extremely low for long periods. This could have ecological and clinical importance for the aquatic and terrestrial fauna at these latitudes.     

The Effect of pH on Copper Toxicity to Blue-Green Algae

The effect of pH on copper toxicity to two planktonic blue-green algae, Aphanizomenon gracile and Oscillatoria redekei, was investigated. Growth rates of the algae without copper treatment decrease with pH, Aphanizomenon is earlier and more affected than Oscillatoria. On the other hand, pH-lowering leads sooner to a toxicity enhancement in Oscillatoria. In the acid range, toxicity retardation occurs in Aphanizomenon. At pH 5.1, shortening of the interval between copper toxicity and copper stimulus is characteristic for both species.