Integrated cultivation of salmonids and seaweeds in open systems

Bacterial abundance and production in a vertical profile in Lake Kariba (17dgS), Zimbabwe, were affected by solar irradiance. At the surface, 1.87 × 10⁹ bacteria 1^–1 were found and abundance peaked at 10 m (2.5 × 10⁹ bacteria l^-1), then decreasing with depth. Bacterial reproduction at the surface(0.145 µg C1^–1 h^–1) was nearly four times less than the production at 10 m although bacterial numbers were only 26% less. Thus, bacterial production per cell was lower at the surface than deeper down, suggesting that bacterial production is inhibited at the surface.Bacterial production in GF/F filtered lake water in Whirl Pack bags showed an exponential decrease down to 3 m depth. The inhibition was well in accordance with light extinction in the UV region. Phosphatase activity was low in light exposed bags compared to dark, indicating photolysis of extracellular enzymes, or phototransformation of recalcitrant DOM, which substitutes enzyme activity. Hypolimnetic enzyme activity was less affected by solar light than epilimnetic.     

Characterization of aggregates produced by the potential mycoherbistat Plectosporium alismatis in submerged culture: germination,UV-radiation tolerance and infectivity

Plectosporium alismatis, a potential mycoherbistat of Alismatacae spp., has been previously shown to produce aggregates which contain chlamydospores in liquid culture. Weevaluated the impact of medium composition on the formation and composition of aggregates. In shake flasks cultures using 5.74 gL^?1 sodium nitrate, 8.8 gL^?1 malt extract or glucose and 0.1% Tween 80, P. alismatis formed small, uniform (diameter of 75% aggregates <720 µm), dense, melanised aggregates containing 10⁴ conidia and 10³ chlamydospores, these numbers remained unchanged during growth. All 7-day-old aggregates exposed to desiccation or/ and UV-radiation germinated. In bioassays using leaf discs of Alisma plantago-aquatica, P. alismatis aggregates caused necrosis, regardless of whether aggregates had been exposed to desiccation and/or UV-radiation prior to application on leaf discs, whereas other propagules (10³ propagules disc^?1) exposed to drying and UV-radiation stress were unable to cause necrosis. This preliminary research shows the potential of aggregates to be used as part of a formulation of biocontrol agents, provided adequate conditions for optimal aggregate yields are found.     

Effect of ultraviolet radiation on chlorophyll,carotenoid, protein and proline contents of some annual desert plants

Investigation was carried out to find whether enhanced ultraviolet radiation influences the Malva parviflora L., Plantago major L., Rumex vesicarius L. and Sismbrium erysimoids Desf. of some annual desert plants. The seeds were grown in plastic pots equally filled with a pre-sieved normal sandy soil for 1 month. The planted pots from each species were randomly divided into equal groups (three groups). Plants of the first group exposed to white-light tubes (400–700 nm) 60 w and UV (365 nm) 8 w tubes. The second group was exposed to white-light tubes (400–700 nm) 60 w and UV (302 nm) 8 w tubes. The third group was exposed to white-light tubes (400–700 nm) 60 w and UV (254 nm) 8 w tubes, respectively, for six days. The results indicated that the chlorophyll contents were affected by enhanced UV radiation. The chlorophyll a, b, and total contents were decreased compared with the control values and reduced with the enhanced UV radiation, but the carotenoid was increased compared with the control and also reduced with the enhanced UV radiation. So, the contents of chlorophylls varied considerably. M. parviflora showed the highest constitutive levels of accumulated chlorophyll a, b, and total chlorophyll (0.463, 0.307 and 0.774 mg g⁻¹ f w) among the investigated plant species. P. major showed the lowest constitutive levels of the chloroplast pigments, 0.0036, 0.0038 and 0.0075 mg g⁻¹ f w for chlorophyll a, b, and total chlorophyll at UV-365 nm, respectively. The protein content was decreased significantly in both root and shoot systems compared with the control values but, it was increased with increasing wave lengths of UV-radiation of all tested plants. R. vesicarius showed the highest protein contents among the investigated plants; its content was 3.8 mg g⁻¹ f w at UV-365 nm in shoot system. On the other hand, decreasing ultraviolet wave length induced a highly significant increase in the level of proline in both root and shoot of all tested plants. From the results obtained, it is suggested that proline can protect cells against damage induced by ultraviolet radiation. Statistically, the variations of the studied metabolic activities were significant due to UV radiation treatment in shoot and root system of all investigated plant species.     

Exploring the common molecular basis for the universal DNA mutation bias: Revival of Löwdin mutation model

Recently, numerous genome analyses revealed the existence of a universal G:C → A:T mutation bias in bacteria, fungi, plants and animals. To explore the molecular basis for this mutation bias, we examined the three well-known DNA mutation models, i.e., oxidative damage model, UV-radiation damage model and CpG hypermutation model. It was revealed that these models cannot provide a sufficient explanation to the universal mutation bias. Therefore, we resorted to a DNA mutation model proposed by Löwdin 40 years ago, which was based on inter-base double proton transfers (DPT). Since DPT is a fundamental and spontaneous chemical process and occurs much more frequently within GC pairs than AT pairs, Löwdin model offers a common explanation for the observed universal mutation bias and thus has broad biological implications.     

紫外辐射诱导桃蚜DNA变异

利用微卫星标记技术分析了不同剂量紫外线诱导下桃蚜(Myzus persicae)的DNA变异与分子多态性.根据3种引物的扩增图谱测出反映遗传变异程度的参数——多态位点率和基因多样度,并进行了方差分析和聚类分析.结果表明,不同紫外线照射时间(2、4和6 h)和照射强度(15、30和45 W)处理后,F₁代桃蚜产生可遗传的变异致使F₂代的DNA发生变异,且变异大小是由辐射时间和强度共同决定的 .F₂代对照与2 、4 和6 h的处理平均多态位点率之间差异显著.对于平均基因多样性,除2 h处理外其余处理均与对照差异显著,且2 h 处理低于对照;根据遗传距离将桃蚜分为对照、2 h(15和30 W)和其余处理3大类群,此聚类分析与前述方差结果一致.     

Ultraviolet irradiation effects on serotinous shape Leucadendron laureolum seeds: altered seed physiology and ultrastructure,and seedling performance

Dry seeds of Leucadendron laureolum (Lam.) Fourc. (Proteaceae) were exposed for different intervals (range: 7 to 84 days) to visible, UV-A and UV-B radiation of different biologically effective dose (range: 0 to 11.43 kJ m^-2 d^-1). Changes in seed germination, physiology and ultrastructure, and residual UV effects on seedling performance, were examined. Germination was depressed in seeds following short (7-day) exposures to UV radiation. This depression was intensified with increased UV exposure dose, and most pronounced at shorter UV-B wavelengths. Also glutathione reductase (GR) activities increased in seeds exposed to shorter UV-B wavelengths, but these were unaffected by irradiation dose level in the UV-B range. Electrolyte leakage rates from UV-irradiated seeds were unaltered, which indicated that germination depression did not result from intrinsic membrane damage. The reversal of germination depression (UV-induced dormancy) in UV-irradiated seeds by red light pointed to the possible involvement of phytochrome in this photo-response. Germination depression disappeared in seeds after 56-days irradiation, possibly due to photoreceptor damage by excess UV light. At this stage, all UV irradiated seeds, irrespective of treatment wavelength or dose level, exhibited increased electrolyte leakage rates, which indicated membrane perturbation. Also, increased GR activities were observed in irradiated seeds, but these were proportionately smaller in seeds exposed to shorter wavelength UV-B radiation (9.1 to 35.8% increase) than longer wavelength UV-A (73.4% increase) and visible (97.7% increase) radiation. This implied a metabolic limitation for scavenging of free radicals and peroxides in aging seeds exposed to UV-B radiation, which pointed to accelerated seed deterioration. It was indirectly supported by ultrastructural evidence of sub-cellular damage (lipid coagulation and plasmalemma withdrawal from cell walls) in embryonic tissues of seeds after 84 days UV-B exposure, and reflected in decreased leaf numbers, photochemical efficiencies, and foliar chlorophyll a and carotenoid levels in seedlings cultured from these seeds.     

Effect of UV radiation on photoinhibition of marine macrophytes in culture systems

The present study examined the effect of UV andphotosynthetically active radiation (PAR) onphotoinhibition and recovery in the Phaeophyte Macrocystis pyrifera, the Rhodophyte Chondruscrispus and the Chlorophyte Ulva lactuca underoutdoor culture conditions. There was an increase inphotoinhibition as a consequence of high exposure toUV-B radiation in M. pyrifera, however, highlevels of PAR accounted for most of thephotoinhibition in C. crispus and U.lactuca. Photodamage by UV-A, UV-B and PAR wascompletely repaired within 5 h and effective quantumyield reached pretreatment values in the three speciesstudied. Species were less susceptible tophotoinhibition after being incubated for 5 d underhigh exposures of natural irradiance suggesting aphotoadaptive process. The recovery of the effectivequantum yield was impaired by long exposure to highlevels of UV-B in C. crispus and UV-A, UV-B andPAR in M. pyrifera. This suggests a differentkind of damage by UV-A and PAR radiation, one to thephotosynthetic apparatus and another which affects therepair mechanism of some species. There was anincrease in UV-absorption ( 330 nm) in M. pyrifera and C. crispus within four days ofthe initiation of the experiment suggesting that thesespecies photoprotect their photosynthetic system whenexposed to elevated UV and PAR levels.     

Hymenobacter amundsenii sp. nov. resistant to ultraviolet radiation,isolated from regoliths in Antarctica

A group of thirteen bacterial strains was isolated from rock samples collected in a deglaciated northern part of James Ross Island, Antarctica. The cells were rod-shaped, Gram-stain-negative, non-motile, catalase positive, and produced moderately slimy, ultraviolet light (UVC)-irradiation-resistant and red–pink pigmented colonies on R2A agar. A polyphasic taxonomic approach based on 16S rRNA gene sequencing, extensive biotyping, fatty acid profile, chemotaxonomy analyses, and whole genome sequencing were applied in order to clarify the taxonomic position of these isolates. Phylogenetic analysis based on the 16S rRNA gene indicated that all isolates constituted a coherent group belonging to the genus Hymenobacter. The closest relatives to the representative isolate P5136^T were Hymenobacter psychrophilus BZ33r^T and Hymenobacter rubripertinctus CCM 8852^T, exhibiting 97.53% and 97.47% 16S rRNA pairwise similarity, respectively. Average nucleotide identity calculated from the whole-genome sequencing data supported the finding that P5136^T represents a distinct Hymenobacter species. The major components in fatty acid profiles were Summed Feature 3 (C_16:1 ω7c/C_16:1 ω6c), C_16:1 ω5c, C_15:0 iso and C_15:0 anteiso. The cellular quinone content contained unanimously menaquinone MK-6 and MK-7 (ratio 1:5.1). The predominant polar lipid was phosphatidylethanolamine, and moderate to minor amounts of two unknown polar lipids, two unknown aminolipids, one unknown glycolipid and two unknown glycophospholipids were present. The G + C content of genomic DNAs is 60.31 mol%. Based on all the obtained results, we propose a novel species for which the name Hymenobacter amundsenii sp. nov. is suggested, with the type strain P5136^T (= CCM 8682^T = LMG 29687^T).     

Role of pigmentation in protecting Bacillus sp. endospores against environmental UV radiation

Bacillus endospores show different kinds of pigmentation. Red-pigmented spores of Bacillus atrophaeus DSM 675, dark-gray spores of B. atrophaeus(T) DSM 7264 and light-gray spores of B. subtilis DSM 5611 were used to study the protective role of the pigments in their resistance to defined ranges of environmental UV radiation. Spores of B. atrophaeus DSM 675 possessing a dark-red pigment were 10 times more resistant to UV-A radiation than those of the other two investigated strains, whereas the responses to the more energetic UV-B and UV-C radiation were identical in all three strains. The methanol fraction of the extracted pigment from the spores absorbs in the associated wavelength area. These results indicate that the carotene-like pigment of spores of B. atrophaeus DSM 675 affects the resistance of spores to environmental UV-A radiation.     

Effects of UV radiation on five marine microphytobenthic Wadden sea diatoms isolated from the Solthörn tidal flat (Lower Saxony,southern North Sea) – Part I: growth and antioxidative defence strategies

The unconsolidated sediment of intertidal mudflats constitutes a highly unstable environment, due to continuously changing water levels and currents as well as temporary exposure to the air. Therefore, diatoms inhabiting marine intertidal areas are subjected to strongly changing surface light and UV intensities due to exposure at low tide. Five marine intertidal diatoms (Achnanthes exigua, Cocconeis peltoides, Diploneis littoralis, Navicula digitoradiata and Amphora exigua) were isolated from the Solthörn tidal flat (Lower Saxony, southern North Sea). Semi-continuous cultures were used to determine the effect of UV radiation (photosynthetically active radiation only [PAR], PAR+UV-B, PAR+UV-A, PAR+UV-B+UV-A) during short- and long-term exposure (6 h or 30 days). Growth rates, chlorophyll a (chl a), antioxidant capacities, accumulation of phenolic compounds (e.g. flavonoids) and DMSP, and activities of antioxidant enzymes (superoxide dismutase, ascorbate peroxidase, monodehydroascorbate reductase and glutathione reductase) were assessed. UV-A had only minor effects on cells, while growth rate, chl a content and protein content were significantly reduced after long-term UV-B exposure. Achnanthes exigua extracts showed the highest antioxidant capacity. The highest activity of SOD, APX and MDHAR was found under long-term combined UV exposure (PAR+UV-B+UV-A). Overall, the antioxidative defence of the five isolates was stimulated during exposure to UV radiation, as may be found during emersion. Emersion induces oxidative stress and, as a result, growth of the five diatom taxa was inhibited to suit changing environmental conditions. All five taxa tested in the present study showed species-specific acclimatization potentials, providing possible explanations for variability in population, species composition and ecosystem structures in the face of climatic variations.