Ahmed A. Issa

Cyanobacteria as a biosorbent of heavy metals in sewage water

The effect of sewage water on some physiological activities of cyanobacteria was studied. Metal-tolerant cyanobacterium (Nostoc linckia) and metal-sensitive (Nostoc rivularis) were grown at three levels of sewage water (25, 50 and 75%). The growth rate showed significant stimulation in low and moderate levels (50% for N. linckia and 25% for N. rivularis). Not only the number of cells was elevated but also, the time required to reach the exponential and the stationary phases was reduced. Also, low levels of sewage water increased chl.a content, photosynthetic O(2)-evolution, respiration and protein content. Similarly, heterocyst frequency as well as nitrogenase activity were increased in cyanobacteria grown at low and moderate levels (25 and 50% sewage). On the other hand, the high level of waste (75%) reduced growth and metabolic activities of the two species. N. linckia accumulated about 30-fold of Zn and ten-fold of Cd than those of growth medium (50% sewage water). Also, N. rivularis accumulated about ten-fold of Zn and two-fold of Cd. The distribution of Cd and Zn in cells were investigated. About 65-60% of Cd or Zn were found in pellets (sediment) as insoluble form in the two species. The soluble form (cytosolic fraction) after being fractionated on sephadex G-(75-100) revealed two peaks with molecular weights of 70-75 and 40-45 kDa. These peaks were in coincidence with Cd and Zn maxima. Nostoc rivulais showed more sensitivity to heavy metals than N. linckia, and accumulated less amount of metal-binding proteins. Nostoc linckia seems to be tolerant to heavy metals (Zn and Cd) and is able to accumulate this metal by adsorption on the pellets (cell surface) and/or through sequestration via metal-binding protein. Therefore it can be recommended it to be employed in the purification of waste contaminated with these heavy metals.

Antibiotic production by the cyanobacteria Oscillatoria angustissima and Calothrix parietina

The accumulation of antibiotic in the medium is temperature dependent and not in direct proportion to growth parameters. The cyanobacterial product suppressed growth of some natural isolates of cyanobacteria and green algae. It inhibits the growth rate and oxygen evolution of the green alga, Chlorella fusca. The antibiotic also inhibits the growth of bacteria and some fungi, especially the dermatophytes. Generally eukaryotic organisms were less sensitive than prokaryotic. Experimental mice were unaffected by the antibiotic. The Oscillatoria antibiotic does not structurally resemble to cyanobacterin.

Proline alleviates heavy metal stress in Scenedesmus armatus.

Growth and some metabolic activities ofScenedesmus armatus grown in the presence of different heavy metals (Cd, Mn and Ni) with and without exogenously added proline (Pro) were monitored. The growth ofS. armatus cells (cell concentration, pigment and dry mass) was inhibited by all these heavy metals. Addition of Pro to the culture medium minimized the toxic effect of the metals. The growth rate was somewhat higher in Pro-containing cultures and started to decline I d later than in cultures containing heavy metals alone.S. armatus cells accumulated the added Pro in response to heavy metals. The accumulation correlated with protein content. Cd was the strongest inducer of Pro accumulation, Mn being the weakest. Cells accumulated nickel more than cadmium and manganese. Heavy metal-treated cells had increased peroxidase and catalase activities.

Membrane stabilization and survival of dehydratedChlorella fusca cells induced by calcium

Chlorella fusca was subjected to evaporative dehydration under air humidity of 72%. Ca2+ pretreated cultures lost water as rapidly as untreated cultures. Nevertheless, an ameliorative effect of Ca2+ pretreatment in droughted cells was found as membrane stability index was improved and K+ leakage was reduced. In addition, higher chlorophyll content and stability was observed. These parameters enabled droughted cells to recommence growth upon rewatering. Thus Ca2+ might increase survival ofC. fusca cells subjected to drought through membrane stabilization.

Spatio-temporal, environmental factors, and host identity shape culturable-epibiotic fungi of seaweeds in the Red Sea, Egypt

The study of fungal species diversity from marine algae is in its infancy; as now no studies have been carried out on the distribution and diversity of fungi on the surfaces of marine macroalgae where all fungal–algal interactions tend to begin. The aim of this study was to isolate and describe the culturable part of mycobiota associated with the surface of benthic marine macroalgae (epiphytic or epibiotic fungi). This is an important step in understanding their abundance, diversity and factors influencing their variability and composition. The fungal community was dominated by Ascomycetes (89%) with Eurotiales as the most abundant fungal order followed by Capnodiales, Pleosporales, and Hypocreales, while Zygomycetes was less frequent. The nature of occurrence of fungal genera on different macroalgal hosts suggests that a mix of generalists’ framework applies to fungal epiphytes of seaweeds, but the abundance of fungal taxa varied among ecological functional groups of algae, as well as macroalgal taxonomic groups, which imply host filtering. The fungal assemblages were also characterized by temporal variation with variation in temperature, pH, and salinity as the most important abiotic factors. The structure of fungal assemblages showed high beta diversity and low similarity between hosts.

Influence of selenium on toxicity of some heavy metals in the green algaScenedesmus obliquus

The green algaScenedesmus obliquus was incubated with heavy metals (Cd2+, Zn2+, Mn2+, Ni2+) with and without selenium.S. obliquus exhibited higher rates of growth and some metabolic activities in cultures containing 0.1 mmol/L Se than those only containing the heavy metals. The positive effect of Se was found with all metals but was negligible with Mn2+.

Impact of Harsh Environmental Conditions on Nodule Formation and Dinitrogen Fixation of Legumes

Dinitrogen (N2) comprises almost 80% of the atmosphere. The triple-bonded molecule cannot be used directly by higher plant. The element nitrogen, or “azote,” meaning “with‐ out life,” as Antonie Lavoisier called it about 200 years ago, has proved to be anything but lifeless, since it is a component of food, poisons, fertilizers, and explosives (Schoot Ui‐ terkamp 1990). The atmosphere contains about 1015 tonnes of N2 gas, and the nitrogen cy‐ cle involves the transformation of some 3 × 109 tonnes of N2 per year on a global basis (Postgate 1982). However, transformations (e.g., N2 fixation) are not exclusively biologi‐ cal. Lightening probably accounts for about 10% of the world’s supply of fixed nitrogen (Sprent and Sprent 1990). The fertilizer industry also provides very important quantities of chemically fixed nitrogen. World production of fixed nitrogen from dinitrogen for chemical fertilizer accounts for about 25% of the Earth’s newly fixed N2, and biological processes account for about 60%. Nitrogen availability is probably the second most limit‐ ing factor in agricultural production, second only to water availability (Date 2000). The le‐ gume-Rhizobium symbiosis is the single most important source of biologically fixed nitrogen in agricultural systems (Graham and Vance 2000). Since it is a biological proc‐ ess, it does not depend on external sources of energy, except for free and renewable sun‐ light, and has few detrimental ecological effects (Phillips 1999).

Spatio temporal and environmental factors influencing macroalgal β diversity in the Red Sea, Egypt

Abstract β Diversity is an ecological concept used to describe the turnover of species across a wide range of spatial and temporal scales, but such knowledge is lacking for macroalgal assemblages of the Red Sea. β Diversity patterns for Red Sea macroalgae were evaluated from different sites (Hurghada, Safaga, and Al-Quseir) and seasons across different environmental disturbances. β Diversity was studied by partitioning the total number of species (γ diversity) into additive components. Geographical heterogeneity was more important than seasonal heterogeneity in structuring macroalgae both at species and functional group levels. Species replacement as a component of β diversity produced dissimilarity in species composition and taxonomic structure. Replacement of species between sites was responsible for the presence of new functional groups of macroalgae. High β diversity and taxonomic similarity values were characteristic of the macroalgae of the Red Sea. The occurrence of small macroalgal thalli that have short life cycles induced high species replacement and subsequently high β diversity, with spatial heterogeneity and environmental gradient as drivers of β diversity. Anthropogenic disturbance at the Safaga site was suggested to induce variation of macroalgal assemblages and functional groups. Excluding rare species from the data set did not change the high values of b diversity.

Effect of manganese and calcium deficiency on the growth and oxygen exchange of Scenedesmus intermedius cultured for successive generations.

The green algaScenedesmus intermedius was grown in synchronous culture under manganese or calcium deficiency for six successive generations. The growth rate, pigment and protein contents gradually decreased in comparison with the control. In Mn-deficient cells, the rate of oxygen evolution was sharply decreased. This inhibition was restored to normal in less than 1 h (40–60 min) by adding Mn salt to the suspension medium. In Ca-deficient cells, the inhibition of photosynthesis appears to be irreversible.

In Vitro Comparative Evaluation of Antioxidant Activity of Hydrophobic and Hydrophilic Extracts from Algicolous Fungi

ABSTRACT The screening of potential antioxidant activities of hydrophobic (ethyl acetate) and hydrophilic (polysaccharide) extracts from both mycelia and fermentation media of eleven algicolous fungi was performed using three antioxidant assays. Algicolous fungi were able to ferment low-cost nutrients composed of potato infusion, glucose, and natural seawater and produce hydrophobic and hydrophilic metabolites with antioxidant properties. Significant differences were observed in antioxidant activities of extracts from the various species evaluated using total antioxidant activity (TAA), hydroxyl radical scavenging activity (HRSA), and ferric reducing antioxidant power (FRAP), as well as their total sugar contents (TSC) of hydrophilic extracts and total phenolic contents (TPC) of hydrophobic extracts. TSC of endopolysaccharides was higher than exopolysaccharides and showed a significant correlation with both TAA and FRAP. Most of mycelial extracts were richer in phenolics than fermentation media, and TPC of hydrophobic extracts was significantly correlated with their FRAP. Mycelial extracts for most of algicolous fungi showed higher antioxidant activities than fermentation media. Both hydrophobic and hydrophilic extracts of algicolous fungi showed good antioxidant properties, especially as hydrogen-donating antioxidants, which could be considered for future applications in medicine, food production, or cosmetic industry.