Ecophysiological analysis reveals distinct environmental preferences in closely related Baltic Sea picocyanobacteria

Cluster 5 picocyanobacteria significantly contribute to primary productivity in aquatic ecosystems. Estuarine populations are highly diverse and consist of many co-occurring strains, but their physiology remains largely understudied. In this study, we characterized 17 novel estuarine picocyanobacterial strains. Phylogenetic analysis of the 16S rRNA and pigment genes (cpcB and cpeBA) uncovered multiple estuarine and freshwater-related clusters and pigment types. Assays with five representative strains (three phycocyanin rich and two phycoerythrin rich) under temperature (10–30°C), light (10–190 μmol photons m⁻² s⁻¹), and salinity (2–14 PSU) gradients revealed distinct growth optima and tolerance, indicating that genetic variability was accompanied by physiological diversity. Adaptability to environmental conditions was associated with differential pigment content and photosynthetic performance. Amplicon sequence variants at a coastal and an offshore station linked population dynamics with phylogenetic clusters, supporting that strains isolated in this study represent key ecotypes within the Baltic Sea picocyanobacterial community. The functional diversity found within strains with the same pigment type suggests that understanding estuarine picocyanobacterial ecology requires analysis beyond the phycocyanin and phycoerythrin divide. This new knowledge of the environmental preferences in estuarine picocyanobacteria is important for understanding and evaluating productivity in current and future ecosystems.     

SEASONAL DIFFERENCES IN THE TEMPERATURE RANGES OF GROWTH OF VIRGINIA ALGAE1

One hundred and fifteen clonal, unialgal strains were isolated and tested for their ability to grow over a range of temperatures from 2 to 40° C. Responses of 63 strains isolated from habitats that were 6° C when sampled and 52 strains isolated from habitats that were 20° C when sampled showed trends toward increasing adaptation to cold or warm temperatures commensurate with their seasonal in situ temperatures. Based on temperature-growth responses alone, 24% of the plankton isolates and 17% of the periphyton isolates could be perennial within the natural habitats. At 5° C, 56% of the warm water plankton isolates and 48% of the warm water periphyton isolates were incapable of growth and, therefore, probably could not be important components of the winter algal community. Likewise at 25° C, 25% of the cold water plankton isolates and 13% of the cold water periphyton isolates were incapable of growth. Thus, temperature alone probably is an important variable regulating seasonal changes in algal community structure. Pollution of these habitats by a thermal enrichment averaging + 5° C year-round could effect a pronounced change in algal species composition because many more taxa could be perennial and more taxa would be incapable of growth during naturally warm periods.     

Winter bloom of picoeukaryotes in Hungarian shallow turbid soda pans and the role of light and temperature

The seasonal dynamics of picophytoplankton communities in shallow turbid alkaline pans in Hungary was studied between July 2006 and May 2007. Similarly to other aquatic environments in the temperate zone, dominance of picocyanobacteria was observed in summer and that of picoeukaryotes in winter. The mild winter in 2006–2007, with midday water temperatures of 5–10°C, resulted in large winter phytoplankton blooms (maximum chlorophyll a concentration 800 μg l^?1) in the shallow pans. The phytoplankton was composed of single-celled picoeukaryotes and had a maximum of 108 × 10⁶ cells ml^?1 in Büdös-szék pan, 50 × 10⁶ cells ml^?1 in Kelemen-szék pan in April 2007, and 47 × 10⁶ cells ml^?1 in Zab-szék pan in March 2007. In order to explain the winter dominance of picoeukaryotes, we isolated picoeukaryotic and picocyanobacterial strains and determined the temperature and light dependence of their photosynthesis. Under temperatures <15°C, the photosynthetic activity of the picoeukaryotic strain was higher and their light utilization was better than those of the picocyanobacterial strain. The results indicate that low temperature and light intensity in winter provide a competitive advantage to picoeukaryotes, while higher temperatures and light intensity are more favorable for picocyanobacteria.     

Effects of recent warm and cold spells on European plant phenology

Climate change is already altering the magnitude and/or frequency of extreme events which will in turn affect plant fitness more than any change in the average. Although the fingerprint of anthropogenic warming in recent phenological records is well understood, the impacts of extreme events have been largely neglected. Thus, the temperature response of European phenological records to warm and cold spells was studied using the COST725 database. We restricted our analysis to the period 1951–2004 due to better spatial coverage. Warm and cold spells were identified using monthly mean ENSEMBLES temperature data on a 0.5° grid for Europe. Their phenological impact was assessed as anomalies from maps displaying mean onsets for 1930–1939. Our results clearly exhibit continental cold spells predominating in the period 1951–1988, especially during the growing season, whereas the period from 1989 onwards was mainly characterised by warm spells in all seasons. The impacts of these warm/cold spells on the onset of phenological seasons differed strongly depending on species, phase and timing. “False” phases such as the sowing of winter cereals hardly reacted to summer warm/cold spells; only the sowing of summer cereals mirrored spring temperature warm/cold spells. The heading dates of winter cereals did not reveal any consistent results probably due to fewer warm/cold spells identified in the relevant late spring months. Apple flowering and the harvest of winter cereals were the best indicators of warm/cold spells in early spring and summer, also being spatially coherent with the patterns of warm/cold spells.     

Diversity and phylogeny of Baltic Sea picocyanobacteria inferred from their ITS and phycobiliprotein operons

Picocyanobacteria of the genus Synechococcus span a range of different colours, from red strains rich in phycoerythrin (PE) to green strains rich in phycocyanin (PC). Here, we show that coexistence of red and green picocyanobacteria in the Baltic Sea is widespread. The diversity and phylogeny of red and green picocyanobacteria was analysed using three different genes: 16S rRNA-ITS, the cpeBA operon of the red PE pigment and the cpcBA operon of the green PC pigment. Sequencing of 209 clones showed that Baltic Sea picocyanobacteria exhibit high levels of microdiversity. The partial nucleotide sequences of the cpcBA and cpeBA operons from the clone libraries of the Baltic Sea revealed two distinct phylogenetic clades: one clade containing mainly sequences from cultured PC-rich picocyanobacteria, while the other contains only sequences from cultivated PE-rich strains. A third clade of phycourobilin (PUB) containing strains of PE-rich Synechococcus spp. did not contain sequences from the Baltic Sea clone libraries. These findings differ from previously published phylogenies based on 16S rRNA gene analysis. Our data suggest that, in terms of their pigmentation, Synechococcus spp. represent three different lineages occupying different ecological niches in the underwater light spectrum. Strains from different lineages can coexist in light environments that overlap with their light absorption spectra.     

Some like it cold: Temperature‐dependent habitat selection by narwhals

The narwhal (Monodon monoceros) is a high‐Arctic species inhabiting areas that are experiencing increases in sea temperatures, which together with reduction in sea ice are expected to modify the niches of several Arctic marine apex predators. The Scoresby Sound fjord complex in East Greenland is the summer residence for an isolated population of narwhals. The movements of 12 whales instrumented with Fastloc‐GPS transmitters were studied during summer in Scoresby Sound and at their offshore winter ground in 2017–2019. An additional four narwhals provided detailed hydrographic profiles on both summer and winter grounds. Data on diving of the whales were obtained from 20 satellite‐linked time‐depth recorders and 16 Acousonde? recorders that also provided information on the temperature and depth of buzzes. In summer, the foraging whales targeted depths between 300 and 850 m where the preferred areas visited by the whales had temperatures ranging between 0.6 and 1.5°C (mean = 1.1°C, SD = 0.22). The highest probability of buzzing activity during summer was at a temperature of 0.7°C and at depths > 300 m. The whales targeted similar depths at their offshore winter ground where the temperature was slightly higher (range: 0.7–1.7°C, mean = 1.3°C, SD = 0.29). Both the probability of buzzing events and the spatial distribution of the whales in both seasons demonstrated a preferential selection of cold water. This was particularly pronounced in winter where cold coastal water was selected and warm Atlantic water farther offshore was avoided. It is unknown if the small temperature niche of whales while feeding is because prey is concentrated at these temperature gradients and is easier to capture at low temperatures, or because there are limitations in the thermoregulation of the whales. In any case, the small niche requirements together with their strong site fidelity emphasize the sensitivity of narwhals to changes in the thermal characteristics of their habitats.     

Lake Superior supports novel clusters of cyanobacterial picoplankton

Very little is known about the biodiversity of freshwater autotrophic picoplankton (APP) in the Laurentian Great Lakes, a system comprising 20% of the world's lacustrine freshwater. In this study, the genetic diversity of Lake Superior APP was examined by analyzing 16S rRNA gene and cpcBA PCR amplicons from water samples. By neighbor joining, the majority of 16S rRNA gene sequences clustered within the "picocyanobacterial clade" consisting of freshwater and marine Synechococcus and Prochlorococcus. Two new groups of Synechococcus spp., the pelagic Lake Superior clusters I and II, do not group with any of the known freshwater picocyanobacterial clusters and were the most abundant species (50 to 90% of the sequences) in samples collected from offshore Lake Superior stations. Conversely, at station Portage Deep (PD), located in a nearshore urbanized area, only 4% of the sequences belonged to these clusters and the remaining clones reflected the freshwater Synechococcus diversity described previously at sites throughout the world. Supporting the 16S rRNA gene data, the cpcBA library from nearshore station PD revealed a cosmopolitan diversity, whereas the majority of the cpcBA sequences (97.6%) from pelagic station CD1 fell within a unique Lake Superior cluster. Thus far, these picocyanobacteria have not been cultured, although their phylogenetic assignment suggests that they are phycoerythrin (PE) rich, consistent with the observation that PE-rich APP dominate Lake Superior picoplankton. Lastly, flow cytometry revealed that the summertime APP can exceed 10(5) cells ml-1 and suggests that the APP shifts from a community of PE and phycocyanin-rich picocyanobacteria and picoeukaryotes in winter to a PE-rich community in summer.     

Downward-Shifting Temperature Range for the Growth of Snow-Bacteria on Glaciers of the Tibetan Plateau

Fifty-seven snow-bacteria strains were isolated from the snow of the Zadang and Mengdagangri Glaciers located in the central and southern part of the Tibetan Plateau, respectively. 16S rRNA gene sequence analysis showed that strains isolated from the Zadang Glacier belonged to the Alphaproteobacteria, Gammaproteobacteria, Actinobacteria, Firmicutes and Bacteroidetes, and were dominated by the Firmicutes. Strains from the Mengdagangri Glacier belonged to the Actinobacteria, Alphaproteobacteria and Gammaproteobacteria, and were dominated by the Actinobacteria. Sixty-one percent of the isolates were colored with pigment. Sixty-nine percent of isolates from the Zadang Glacier were psychrotolerants, and there were no psychrophiles. We compared the growth-temperature range of 26 snow-bacteria strains to their closest mesophilic type strains and found that 46% of them had an optimum growth-temperature at or lower than 20°C, and 65% were all able to grow at 0°C. However, only 5.3% of mesophilic strains had optimum growth-temperatures at or lower than 20°C, and 9% could grow at 0°C. Snow-bacteria shift their growth-temperature downward; and doing this, in terms of the minimum and optimum temperatures for growth, might be an important strategy for them to adapt to low temperature after they have been deposited on the glacier. Our results suggested that, in order to adapt from mesophilic environments to a cold habitat, snow-bacteria widen their temperature range for growth, convert from mesophiles to psychrotolerants, but not to psychrophiles. In addition, eight isolates formed pigmented colonies, while their mesophilic counterparts were achromogenic. This helped us to confirm through comparative analysis that pigmented microorganisms were more abundant in high-altitude glaciers than in mesophilic environments.     

Identification of cultured and uncultured picocyanobacteria from a mesotrophic freshwater lake based on the partial sequences of 16S rDNA

Eight cultured strains (OK01, OK02, OK03, OK05, OK07, OK08, OK09, and OK10) of picocyanobacteria were isolated from Lake Okutama. Five cyanobacterial DNA fragments (DGGE bands; B4, B5, B6, B7, and B8) were obtained from the lake water samples by denaturing gradient gel electrophoresis (DGGE) after polymerase chain reaction (PCR) amplification of 16S ribosomal genes. To classify the picocyanobacterial strains and the DGGE bands, a partial sequence of 16S rDNA was used. Among seven strains, OK01, OK07, and OK09 were identified as the genus Synechococcus and OK02 and OK05 as the genus Phormidium. OK03 was identified as the genus Oscillatoria and was closely related to B4 (100% homology). B5, B6, B7, and B8 were related to the genus Synechococcus. These results revealed that the picocyanobacteria in the lake are phylogenetically diverse. PCR-DGGE analysis is a useful tool to determine picocyanobacterial community structure in freshwater environments. Received: February 25, 2001 / Accepted: July 27, 2001     

Do acid-tolerant picocyanobacteria exist? A study of two strains isolated from humic lakes in Poland

The occurrence of picocyanobacteria, the smallest cell-size fraction of cyanobacteria, in low-pH waters, is still poorly studied. In this study, we tested the hypothesis that picocyanobacteria found occasionally in low-pH environments are adapted to such water conditions. We isolated picocyanobacteria by means of the cytometric method from two humic lakes with pH ≤5. We obtained two strains belonging to two cosmopolitan phylogenetic clades of picocyanobacteria: Cyanobium gracile cluster and Subalpine cluster I. Experiments on filtered lake water from low-pH (≤5) and slightly alkaline (pH 8.2) lakes, and with an acidified cyanobacterium medium (pH 4.5) were conducted to test the growth of the isolated picocyanobacteria in various pH conditions. The experimental results of this study showed that some picocyanobacteria strains were acid tolerant, achieving higher growth rates and reaching higher maximum numbers in humic, naturally acidic waters rather than in alkaline waters. We show that despite a close phylogenetic relationship, strains of picocyanobacteria exhibit significant physiological and ecological diversity and that at least some picocyanobacteria have the evolutionary potential to cope with low pH. Characterization of the genetic basis of acid tolerance in picocyanobacteria is important to understand how these microorganisms function in aquatic ecosystems and how their communities may respond to a changing environment.     

Morphology and Phylogenetic Analyses of Three Novel Naegleria Isolated from Freshwaters on Jeju Island,Korea, During the Winter Period

The genus Naegleria is one of the best known heterolobosean groups, and is the causative agent of primary amoebic meningoencephalitis. This group is rarely studied in temperate regions during winter. Here, three novel Naegleria were isolated from freshwaters on Jeju Island, Korea, during winter. Two isolates were amoeboflagellates, and one of the three amoebae did not undergo enflagellation. All amoebae had eruptive pseudopodia, and the layer of refractile granules around a large nucleus. They formed a cyst with ~2 pores in the cyst stage. The amoeboflagellate form had two flagella and no division in the flagellate stage, and no cytostome. These features are very similar to typical Naegleria. Furthermore, our isolates were able to grow at > 30 °C, suggesting that they had different thermophilicity from Naegleria in polar regions. All amoebae were largely encysted at 5 or 10 °C, indicating that they were likely encysted during winter. Based on the 18S rRNA gene and the ITS1‐5.8S rRNA gene‐ITS2 sequences, the phylogenetic analyses consistently revealed that the isolates are members of the Naegleria group. However, the isolates differ from other species in both phylogenetic trees. Thus, Naegleria in cold habitats appeared to have a high degree of novelty, but their thermophilicity may be dependent on locality.     

Divergence of gastropod life history in contrasting thermal environments in a geothermal lake

Experiments using natural populations have provided mixed support for thermal adaptation models, probably because the conditions are often confounded with additional environmental factors like seasonality. The contrasting geothermal environments within Lake Mývatn, northern Iceland, provide a unique opportunity to evaluate thermal adaptation models using closely located natural populations. We conducted laboratory common garden and field reciprocal transplant experiments to investigate how thermal origin influences the life history of Radix balthica snails originating from stable cold (6 °C), stable warm (23 °C) thermal environments or from areas with seasonal temperature variation. Supporting thermal optimality models, warm‐origin snails survived poorly at 6 °C in the common garden experiment and better than cold‐origin and seasonal‐origin snails in the warm habitat in the reciprocal transplant experiment. Contrary to thermal adaptation models, growth rate in both experiments was highest in the warm populations irrespective of temperature, indicating cogradient variation. The optimal temperatures for growth and reproduction were similar irrespective of origin, but cold‐origin snails always had the lowest performance, and seasonal‐origin snails often performed at an intermediate level compared to snails originating in either stable environment. Our results indicate that central life‐history traits can differ in their mode of evolution, with survival following the predictions of thermal optimality models, whereas ecological constraints have shaped the evolution of growth rates in local populations.     

Low-temperature resistance in Polylepis tarapacana, a tree growing at the highest altitudes in the world

The Polylepis tarapacana forests found in Bolivia are unique with respect to their altitudinal distribution (4200–5200 m). Given the extreme environmental conditions that characterize these altitudes, this species has to rely on distinct mechanisms to survive stressful temperatures. The purpose of this study was to determine low‐temperature resistance mechanisms in P. tarapacana. Tissue was sampled for carbohydrate and proline contents and micro‐climatic measurements were made at two altitudes, 4300 and 4850 m, during both the dry cold and wet warm seasons. Supercooling capacity (?3 to ?6 °C for the cold dry and ?7 to ?9 °C for the wet warm season) and injury temperatures (?18 to ?23 °C for both seasons), determined in the laboratory, indicate that P. tarapacana is a frost‐tolerant species. On the other hand, an increase in supercooling capacity, as the result of significant increase in total soluble sugar and proline contents, occurs during the wet warm season as a consequence of higher metabolic activity. Hence, P. tarapacana, a frost‐tolerant species during the colder unfavourable season, is able to avoid freezing during the more favourable season when minimum night‐time temperatures are not as extreme.     

Genetic Diversity of Picocyanobacteria in Tibetan Lakes: Assessing the Endemic and Universal Distributions

The phylogenetic diversity of picocyanobacteria in seven alkaline lakes on the Tibetan Plateau was analyzed using the molecular marker 16S-23S rRNA internal transcribed spacer sequence. A total of 1,077 environmental sequences retrieved from the seven lakes were grouped into seven picocyanobacterial clusters, with two clusters newly described here. Each of the lakes was dominated by only one or two clusters, while different lakes could have disparate communities, suggesting low alpha diversity but high beta diversity of picocyanobacteria in these high-altitude freshwater and saline lakes. Several globally distributed clusters were found in these Tibetan lakes, such as subalpine cluster I and the Cyanobium gracile cluster. Although other clusters likely exhibit geographic restriction to the plateau temporally, reflecting endemicity, they can indeed be distributed widely on the plateau. Lakes with similar salinities may have similar genetic populations despite a large geographic distance. Canonical correspondence analysis identified salinity as the only environmental factor that may in part explain the diversity variations among lakes. Mantel tests suggested that the community similarities among lakes are independent of geographic distance. A portion of the picocyanobacterial clusters appear to be restricted to a narrow salinity range, while others are likely adapted to a broad range. A seasonal survey of Lake Namucuo across 3 years did not show season-related variations in diversity, and depth-related population partitioning was observed along a vertical profile of the lake. Our study emphasizes the high dispersive potential of picocyanobacteria and suggests that the regional distribution may result from adaptation to specified environments.     

Why get big in the cold? Size–fecundity relationships explain the temperature‐size rule in a pulmonate snail (Physa)

Most ectotherms follow a pattern of size plasticity known as the temperature‐size rule where individuals reared in cold environments are larger at maturation than those reared in warm environments. This pattern seems maladaptive because growth is slower in the cold so it takes longer to reach a large size. However, it may be adaptive if reaching a large size has a greater benefit in a cold than in a warm environment such as when size‐dependent mortality or size‐dependent fecundity depends on temperature. I present a theoretical model showing how a correlation between temperature and the size–fecundity relationship affects optimal size at maturation. I parameterize the model using data from a freshwater pulmonate snail from the genus Physa. Nine families were reared from hatching in one of three temperature regimes (daytime temperature of 22, 25 or 28 °C, night‐time temperature of 22 °C, under a 12L : 12D light cycle). Eight of the nine families followed the temperature‐size rule indicating genetic variation for this plasticity. As predicted, the size–fecundity relationship depended upon temperature; fecundity increases steeply with size in the coldest treatment, less steeply in the intermediate treatment, and shows no relationship with size in the warmest treatment. Thus, following the temperature‐size rule is adaptive for this species. Although rarely measured under multiple conditions, size–fecundity relationships seem to be sensitive to a number of environmental conditions in addition to temperature including local productivity, competition and predation. If this form of plasticity is as widespread as it appears to be, this model shows that such plasticity has the potential to greatly modify current life‐history theory.     

Isolation and characterization of new strains of methanogens from cold terrestrial habitats

Five strains of methanogenic archaea (MT, MS, MM, MSP, ZB) were isolated from permanently and periodically cold terrestrial habitats. Physiological and morphological studies, as well as phylogenetic analyses of the new isolates were performed. Based on sequences of the 16S rRNA and methyl-coenzyme M reductase a-subunit (mcrA) genes all new isolates are closely related to known mesophilic and psychrotolerant methanogens. Both, phylogenetic analyses and phenotypic properties allow to classify strains MT, MS, and MM as members of the genus Methanosarcina. Strain MT is a new ecotype of Methanosarcina mazei, whereas strains MM and MS are very similar to each other and can be assigned to the recently described psychrotolerant species Methanosarcina lacustris. The hydrogenotrophic strain MSP is a new ecotype of the genus Methanocorpusculum. The obligately methylotrophic strain ZB is closely related to Methanomethylovorans hollandica and can be classified as new ecotype of this species. All new isolates, including the strains from permanently cold environments, are not true psychrophiles according to their growth temperature characteristics. In spite of the ability of all isolates to grow at temperatures as low as 1-5 degrees C, all of them have their growth optima in the range of moderate temperatures (25-35 degrees C). Thus, they can be regarded as psychrotolerant organisms. Psychrotolerant methanogens are thought to play an important role in methane production in both, habitats under seasonal temperature variations or from permanently cold areas.     

Diverse and dynamic populations of cyanobacterial podoviruses in the Chesapeake Bay unveiled through DNA polymerase gene sequences

Many podoviruses have been isolated which infect marine picocyanobacteria, and they may play a potentially important role in regulating the biomass and population composition of picocyanobacteria. However, little is known about the diversity and population dynamics of autochthonous cyanopodoviruses in marine environments. Using a set of newly designed PCR primers which specifically amplify the DNA pol from cyanopodoviruses, a total of 221 DNA pol sequences were retrieved from eight Chesapeake Bay virioplankton communities collected at different times and locations. All DNA pol sequences clustered with the eight known podoviruses that infect different marine picocyanobacteria, and could be divided into at least 10 different subclusters (I-X). The presence of these cyanopodovirus genotypes based on PCR-amplification of DNA pol gene sequences was supported by the existence of similar DNA pol genotypes with metagenome libraries of Chesapeake Bay virioplankton assemblages. The composition of cyanopodoviruses in the Bay also exhibited distinct winter and summer patterns which were likely related to corresponding seasonal changes in the composition of cyanobacterial populations. Our study suggests that diverse and dynamic populations of cyanopodoviruses are present in the estuarine environment. The PCR method developed in this study provides a specific and sensitive tool to explore the abundance, distribution and phylogenetic diversity of cyanopodoviruses in aquatic environments. Linking the dynamics of host and viral populations in the natural environment is critical to broader characterization of the ecological role of virioplankton within microbial communities.     

Changes in apoplastic peroxidase activity and cell wall composition are associated with cold‐induced morpho‐anatomical plasticity of wheat leaves

• Temperate grasses, such as wheat, become compact plants with small thick leaves after exposure to low temperature. These responses are associated with cold hardiness, but their underlying mechanisms remain largely unknown. Here we analyse the effects of low temperature on leaf morpho‐anatomical structure, cell wall composition and activity of extracellular peroxidases, which play key roles in cell elongation and cell wall thickening, in two wheat cultivars with contrasting cold‐hardening ability.
• A combined microscopy and biochemical approach was applied to study actively growing leaves of winter (ProINTA‐Pincén) and spring (Buck‐Patacón) wheat developed under constant warm (25 °C) or cool (5 °C) temperature.
• Cold‐grown plants had shorter leaves but longer inter‐stomatal epidermal cells than warm‐grown plants. They had thicker walls in metaxylem vessels and mestome sheath cells, paralleled with accumulation of wall components, predominantly hemicellulose. These effects were more pronounced in the winter cultivar (Pincén). Cold also induced a sharp decrease in apoplastic peroxidase activity within the leaf elongating zone of Pincén, and a three‐fold increase in the distal mature zone of the leaf. This was consistent with the enhanced cell length and thicker cell walls in this cultivar at 5 °C.
• The different response to low temperature of apoplastic peroxidase activity and hemicellulose between leaf zones and cultivar types suggests they might play a central role in the development of cold‐induced compact morphology and cold hardening. New insights are presented on the potential temperature‐driven role of peroxidases and hemicellulose in cell wall dynamics of grasses.