Antioxidants characterization in selected cyanobacteria

Antioxidants—molecules that have the ability to inhibit the oxidation of other molecules and have many medicinal and industrial applications—are commonly found in algae. Due to the harmful effects of common synthetic antioxidants, their replacement with natural antioxidants would be advantageous. The goal of this study was to examine the efficacy of antioxidants (including antioxidant content, antioxidant activity and antioxidant enzymes) among 11 species of freshwater blue-green algae. Antioxidant activities were evaluated by assaying radical scavenging activity, reducing power and chelating activity. The results showed that Spirulina platensis has the highest radical scavenging activity and reducing power (524 and 244 % more than the control, respectively) and Nostoc linkia has the highest chelating activity (195 %). Examination of some antioxidant contents such as chlorophyll a, carotenoids and phenolic content revealed that S. platensis has the highest contents [10.6 mg/g dry weight (DW), 2.4 mg/g DW and 9.7 mg gallic acid equivalent /g DW, respectively]. The positive correlation (P <0.01) between algal content and antioxidant activity may be attributed to the potent antioxidant activity of these contents. Variation in the activity of three antioxidant enzymes (superoxide dismutase, catalase and peroxidase) was also reported. This study showed that the Cyanobacteria are promising sources of antioxidants.     

Poly-3-hydroxyalkanoates from marine and freshwater cyanobacteria

Polyesters of (R)-3-hydroxybutanoic and (R)-3-hydroxypentanoic acids have been isolated from Aphanothece species, a freshwater cyanobacteri     

Microbial attachment to particles in marine and freshwater ecosystems

Scanning electron microscopy observations ofin situ suspended marine and freshwater particles show diverse but similar modes of bacterial and fungal attachment. A survey of Sierra Nevada mountain lakes and pelagic and near-shore waters in the Pacific Ocean indicates that attachment is most noticeable in the near-surface waters where fresh dissolved and particulate input of carbon from phytoplankton and elevated temperatures favor microbial growth. The most common modes of attachment are: adhesive stalk formation, growth on adhesive webs, attachment by the use of pili-like appendages and slimy capsular secretions, and molecular or chemical sorption without the use of visualized structural appendages. Attached microbial growth is accelerated when particulate substrates are supplied, even when they are not rich in organic nutrients. This is the case in the Lake Tahoe basin, where microflora attached to eroded silts can significantly modify the organic carbon and nutrient content of such minerogenous particles.     

Analysis of the hli gene family in marine and freshwater cyanobacteria

Certain cyanobacteria thrive in natural habitats in which light intensities can reach 2000 micromol photon m(-2) s(-1) and nutrient levels are extremely low. Recently, a family of genes designated hli was demonstrated to be important for survival of cyanobacteria during exposure to high light. In this study we have identified members of the hli gene family in seven cyanobacterial genomes, including those of a marine cyanobacterium adapted to high-light growth in surface waters of the open ocean (Prochlorococcus sp. strain Med4), three marine cyanobacteria adapted to growth in moderate- or low-light (Prochlorococcus sp. strain MIT9313, Prochlorococcus marinus SS120, and Synechococcus WH8102), and three freshwater strains (the unicellular Synechocystis sp. strain PCC6803 and the filamentous species Nostoc punctiforme strain ATCC29133 and Anabaena sp. [Nostoc] strain PCC7120). The high-light-adapted Prochlorococcus Med4 has the smallest genome (1.7 Mb), yet it has more than twice as many hli genes as any of the other six cyanobacterial species, some of which appear to have arisen from recent duplication events. Based on cluster analysis, some groups of hli genes appear to be specific to either marine or freshwater cyanobacteria. This information is discussed with respect to the role of hli genes in the acclimation of cyanobacteria to high light, and the possible relationships among members of this diverse gene family.     

氮磷营养盐对四种淡水丝状蓝藻生长的影响

通过设定不同的氮、磷营养盐浓度,在实验室条件下研究了不同浓度的氮和磷对4种淡水丝状蓝藻:皮质颤藻、尖细颤藻、蛇形颤藻和坑形细鞘丝藻生长的影响.结果表明,皮质颤藻和坑形细鞘丝藻对高浓度的氮、磷有着较强的适应能力,在硝态氮浓度0.016mg·mL^-1～2.0mg·mL、磷浓度1.36mg·mL^-1～13.6μg·mL时生长较好.4株藻在只存在氨态氮的情况下生长都受到抑制.     

Effects of acidification on olfactory-mediated behaviour in freshwater and marine ecosystems: a synthesis

For many aquatic organisms, olfactory-mediated behaviour is essential to the maintenance of numerous fitness-enhancing activities, including foraging, reproduction and predator avoidance. Studies in both freshwater and marine ecosystems have demonstrated significant impacts of anthropogenic acidification on olfactory abilities of fish and macroinvertebrates, leading to impaired behavioural responses, with potentially far-reaching consequences to population dynamics and community structure. Whereas the ecological impacts of impaired olfactory-mediated behaviour may be similar between freshwater and marine ecosystems, the underlying mechanisms are quite distinct. In acidified freshwater, molecular change to chemical cues along with reduced olfaction sensitivity appear to be the primary causes of olfactory-mediated behavioural impairment. By contrast, experiments simulating future ocean acidification suggest that interference of high CO₂ with brain neurotransmitter function is the primary cause for olfactory-mediated behavioural impairment in fish. Different physico-chemical characteristics between marine and freshwater systems are probably responsible for these distinct mechanisms of impairment, which, under globally rising CO₂ levels, may lead to strikingly different consequences to olfaction. While fluctuations in pH may occur in both freshwater and marine ecosystems, marine habitat will remain alkaline despite future ocean acidification caused by globally rising CO₂ levels. In this synthesis, we argue that ecosystem-specific mechanisms affecting olfaction need to be considered for effective management and conservation practices.     

Formation of thionates by freshwater and marine strains of sulfate-reducing bacteria

The formation of thionates (thiosulfate, trithionate and tetrahionate) during the reduction of sulfate or sulfite was studied with four marine and four freshwater strains of sulfate-reducing bacteria. Growing cultures of two strains of the freshwater species Desulfovibrio desulfuricans formed up to 400 M thiosulfate and 100 M trithionate under conditions of electron donor limitation. Tetrathionate was observed in lower concentrations of up to 30 M. Uncoupler-treated washed cells of the four freshwater strains formed thiosulfate and trithionate at low electron donor concentrations with sulfite in excess. In contrast, only one of four marine strains formed thionates. The freshwater strain Desulfobulbus propionicus transformed sulfite almost completely to thiosulfate and trithionate. The amounts produced increased with time, concentration of added sulfite and cell density. Tetrathionate was detected only occasionally and in low concentrations, and was probably formed by chemical oxidation of thiosulfate. The results confirm the diversity of the sulfite reduction pathways in sulfate-reducing bacteria, and suggest that thiosulfate and trithionate are normal by-products of sulfate reduction.Abbreviations CCCP carbonyl cyanide m-chlorophenylhydrazone     

Growth characteristics of selected thermophilic strains of cyanobacteria using crossed gradients of temperature and light

Growth requirements of 10 possibly thermophilic strains of cyanobacteria were compared under a wide spectrum of light and temperature conditions (7–80Wm^?2, 12–40°C). The strains were isolated from different localities: six of thermal springs in Slovakia (4 from Pie??any, 2 from Sklené Teplice), one from thermal waters in Rupite, Bulgaria, 2 strains from a hypersaline lake Chott-el-Djerid, Tunisia, and one strain from the tropical island of Cebu, Philippines. Although the crossed gradient unit allowed only sub-optimal temperature range with respect to thermophile definition, i.e. optimum temperature above 45°C, there were difference among the strains. The most thermophilic and high-light tolerant strain was Synechococcus bigranulatus strain Lukavsky 2005/66, with a peak above 45°C; the second was Chroococcidiopsis thermalis strain Hindák 2008/9, and Isocystis sp. strain Hindák 2006/1. The temperature requirements of other strains were similar; the least thermophilic were both Slovakian strains of the genus Hapalosiphon. Growth was not limited below 80 W m^?2, except for H. fontinalis strain Hindák 2008/3, which prefers lower irradiance. Hapalosiphon delicatulus strain Hindák 2007/20, isolated from a bark tree on the tropical island of Cebu was rather mesophilic than thermophilic and shade-preferring. The CCA revealed that the ecologically similar strains originated from the same or nearby localities. There were no significant correlations between temperature optima in culture and in nature. Bulgarian and Tunisian strains preferred higher irradiances.     

Selection and characterization of cyanophage resistance in marine Synechococcus strains

Marine viruses are an important component of the microbial food web, influencing microbial diversity and contributing to bacterial mortality rates. Resistance to cooccurring cyanophages has been reported for natural communities of Synechococcus spp.; however, little is known about the nature of this resistance. This study examined the patterns of infectivity among cyanophage isolates and unicellular marine cyanobacteria (Synechococcus spp.). We selected for phage-resistant Synechococcus mutants, examined the mechanisms of phage resistance, and determined the extent of cross-resistance to other phages. Four strains of Synechococcus spp. (WH7803, WH8018, WH8012, and WH8101) and 32 previously isolated cyanomyophages were used to select for phage resistance. Phage-resistant Synechococcus mutants were recovered from 50 of the 101 susceptible phage-host pairs, and 23 of these strains were further characterized. Adsorption kinetic assays indicate that resistance is likely due to changes in host receptor sites that limit viral attachment. Our results also suggest that receptor mutations conferring this resistance are diverse. Nevertheless, selection for resistance to one phage frequently resulted in cross-resistance to other phages. On average, phage-resistant Synechococcus strains became resistant to eight other cyanophages; however, there was no significant correlation between the genetic similarity of the phages (based on g20 sequences) and cross-resistance. Likewise, host Synechococcus DNA-dependent RNA polymerase (rpoC1) genotypes could not be used to predict sensitivities to phages. The potential for the rapid evolution of multiple phage resistance may influence the population dynamics and diversity of both Synechococcus and cyanophages in marine waters.     

Bioaccumulation of manganese in selected tissues of the freshwater crab,Potamonautes warreni (Calman), from industrial and mine-polluted freshwater ecosystems

Manganese concentrations in water and sediments of the Bronkhorstspruit River, Nooitgedacht Dam and especially in the Natalspruit River, did not fall within stated limits for the protection of aquatic life. Tissue manganese concentrations in Potamonautes warreni from the Natalspruit River were generally higher than those in the tissues of crabs from the other two aquatic ecosystems. The highest mean manganese tissue concentration in crabs from the three systems was detected in the carapace (587± 445 µg g^-1 wet weight). It appears that the carapace in these animals acts as a sink in which manganese can be deposited, thus also playing an important role in the detoxification of manganese in these crustaceans. No seasonal or sex-related variation was detected. Body size of the crabs, however, seems to be an important influencing factor in manganese bioaccumulation. A significant increase in carapace manganese concentrations was detected with an increase in body size. However, muscle manganese concentrations were higher in the smaller groups.The concentration factors (BF) calculated for the different tissues with respect to the water were highest in the carapace and ranged from 280.9 to 742.8. The BF with respect to the sediment was comparatively low for all the tissues (0.1 to 0.7). As the manganese concentration in the tissues reflects to some extent the degree of manganese contamination of the surrounding aquatic environment, it appears that P. warreni may be useful as a potential biomonitor of manganese pollution.     

Zoosporic fungi in freshwater ecosystems

A review of the modern state of knowledge of zoosporic fungi in freshwater plankton and benthos is given. The effects of abiotic factors upon the distribution and development of these fungi are discussed, along with the problem of the role zoosporic fungi play in lake ecosystems.     

Assessing the role of large herbivores in the structuring and functioning of freshwater and marine angiosperm ecosystems

While large herbivores can have strong impacts on terrestrial ecosystems, much less is known of their role in aquatic systems. We reviewed the literature to determine: 1) which large herbivores (> 10 kg) have a (semi‐)aquatic lifestyle and are important consumers of submerged vascular plants, 2) their impact on submerged plant abundance and species composition, and 3) their ecosystem functions. We grouped herbivores according to diet, habitat selection and movement ecology: 1) Fully aquatic species, either resident or migratory (manatees, dugongs, turtles), 2) Semi‐aquatic species that live both in water and on land, either resident or migratory (swans), 3) Resident semi‐aquatic species that live in water and forage mainly on land (hippopotamuses, beavers, capybara), 4) Resident terrestrial species with relatively large home ranges that frequent aquatic habitats (cervids, water buffalo, lowland tapir). Fully aquatic species and swans have the strongest impact on submerged plant abundance and species composition. They may maintain grazing lawns. Because they sometimes target belowground parts, their activity can result in local collapse of plant beds. Semi‐aquatic species and turtles serve as important aquatic–terrestrial linkages, by transporting nutrients across ecosystem boundaries. Hippopotamuses and beavers are important geomorphological engineers, capable of altering the land and hydrology at landscape scales. Migratory species and terrestrial species with large home ranges are potentially important dispersal vectors of plant propagules and nutrients. Clearly, large aquatic herbivores have strong impacts on associated species and can be critical ecosystem engineers of aquatic systems, with the ability to modify direct and indirect functional pathways in ecosystems. While global populations of large aquatic herbivores are declining, some show remarkable local recoveries with dramatic consequences for the systems they inhabit. A better understanding of these functional roles will help set priorities for the effective management of large aquatic herbivores along with the plant habitats they rely on.     

Viral abundance and genome size distribution in the sediment and water column of marine and freshwater ecosystems

The size distribution of viral DNA in natural samples was investigated in a number of marine, brackish and freshwater environments by means of pulsed field gel electrophoresis (PFGE). The method was modified to work with both water and sediment samples, with an estimated detection limit for individual virus genome size groups of 1-2 x 10(4) virus-like particles (VLP) mL(-1) water and 2-4 x 10(5) VLP cm(-3) sediment in the original samples. Variations in the composition and distribution of dominant virus genome sizes were analyzed within and between different habitats that covered a range in viral density from 0.4 x 10(7) VLP mL(-1) (sea water) to 300 x 10(7) VLP cm(-3) (lake sediment). The PFGE community fingerprints showed a number of cross-system similarities in the genome size distribution with a general dominance of genomes in the 30-48, 50-70 and 145-200 kb size fractions, and with many of the specific genome sizes detected in all the investigated habitats. However, large differences in community fingerprints were also observed between the investigated sites, and some virus genome sizes were found only in specific biotopes (e.g. lake water), in specific ecosystems (e.g. a particular lake) or even in specific microhabitats (e.g. a particular sediment stratum).     

Genetic engineering in marine cyanobacteria

Many species of microalgae producing useful materials have been isolated from marine environments. For their industrial application, widely applicable and stable gene expression is required. It is necessary to establish gene transfer methods as an essential first step in genetic manipulation. Although gene transfer techniques for cyanobacteria have been developed, only naturally transformable strains have been used. Here, we describe recent progress made in developing gene transfer methods for marine cyanobacteria. The following are covered: (1) transformation, (2) electroporation, (3) conjugation, (4) particle gun. A plasmid from the marine cyanobacterium, Synechococcus sp., whose copy number is dependent on salinity, was characterized. This plasmid is being used to develop a stable and controllable gene expression system.     

Global analysis of nitrogen and phosphorus limitation of primary producers in freshwater, marine and terrestrial ecosystems

The cycles of the key nutrient elements nitrogen (N) and phosphorus (P) have been massively altered by anthropogenic activities. Thus, it is essential to understand how photosynthetic production across diverse ecosystems is, or is not, limited by N and P. Via a large-scale meta-analysis of experimental enrichments, we show that P limitation is equally strong across these major habitats and that N and P limitation are equivalent within both terrestrial and freshwater systems. Furthermore, simultaneous N and P enrichment produces strongly positive synergistic responses in all three environments. Thus, contrary to some prevailing paradigms, freshwater, marine and terrestrial ecosystems are surprisingly similar in terms of N and P limitation.     

Junk-food in marine ecosystems

The abundance and availability of food are critical determininants of reproductive success and population dynamics of marine top predators. However, recent work has indicated that the quality of the food may also be critically important for some marine predators. The 'junkfood hypothesis' was originally suggested as a potential explanation for a dramatic population decline of Stellers sea lions Eumetopias jubatus in the Gulf of Alaska. According to the hypothesis, a dietary switch to prey of low energy content led to detrimental effects on the population of sea lions. A number of observations indicate that the hypothesis is relevant for several population parameters. Recent work on piscivorous seabirds has provided substantial evidence indicating the relevance of this hypothesis in food webs in e.g. the North Pacific, the North Sea and the Baltic Sea. The emergence of 'junk-food' in these systems may be coupled to large scale changes in climatological and oceanographic forcing, although predation, fishing and competition provide additional plausible hypotheses. It may be possible to predict which kinds of animals will be particularly sensitive to food quality; these seem to be species with limited ability to carry food loads, with energetically-expensive foraging behaviour, and with digestive anatomy evolved to minimize mass at the cost of digestive efficiency. This review suggests that the junk-food hypothesis is a highly relevant factor in relation to sustaining ecosystem resilience, and is an important consideration in ecosystem management. Sustaining healthy populations of marine top-predators requires an understanding of the role of food quality, in addition to food abundance and availability.     

Role of fungi in freshwater ecosystems

There are more than 600 species of freshwater fungi with a greater number known from temperate, as compared to tropical, regions. Three main groups can be considered which include Ingoldian fungi, aquatic ascomycetes and non-Ingoldian hyphomycetes, chytrids and, oomycetes. The fungi occurring in lentic habitats mostly differ from those occurring in lotic habitats. Although there is no comprehensive work dealing with the biogeography of all groups of freshwater fungi, their distribution probably follows that of Ingoldian fungi, which are either cosmopolitan, restricted to pantemperate or pantropical regions, or in a few cases, have a restricted distribution. Freshwater fungi are thought to have evolved from terrestrial ancestors. Many species are clearly adapted to life in freshwater as their propagules have specialised aquatic dispersal abilities. Freshwater fungi are involved in the decay of wood and leafy material and also cause diseases of plants and animals. These areas are briefly reviewed. Gaps in our knowledge of freshwater fungi are discussed and areas in need of research are suggested.