Physiological responses induced by copper bioaccumulation in <Emphasis Type="Italic">Eichhornia crassipes</Emphasis> (Mart.)

Eichhornia crassipes (Mart.) has strong ability to remove Cu²⁺ from copper-contaminated water. Physiological responses in E. crassipes exposed to known concentrations of Cu²⁺ were examined in this study, and demonstrated that E. crassipes could accumulate 314 mg kg⁻¹ dry weight of Cu when exposed to 5 mg l⁻¹ of Cu²⁺ for periods up to 14 d. However, there were marked changes in physiology of the plant commencing at Cu²⁺ concentrations of 1 mg l⁻¹. Results of this study showed that E. crassipes could tolerate moderate concentrations (i.e. 0.5 mg l⁻¹) of Cu²⁺, without significant changes in photosynthetic pigment concentrations, while high concentrations (i.e. 5 and 10 mg l⁻¹) of Cu²⁺ resulted in substantial loss in pigment concentrations. Increases in malondiadehyde (MDA) content were also demonstrated in plant exposure to high Cu²⁺ concentrations. Soluble protein content increased to a level slightly higher than the control at <0.5 mg l⁻¹ of Cu²⁺, but then decreased with exposure to >1 mg l⁻¹ of Cu²⁺. Our results suggest that E. crassipes has a substantial capacity to accumulate copper when cultivated at moderate concentrations of Cu²⁺, without marked changes in its physiology. The findings indicate that E. crassipes is a promising possibility for phytoremediation of moderately Cu-contaminated water bodies. Handling editor: S. M. Thomaz     

Activity of some Nile River aquatic macrophyte extracts against the cyanobacterium Microcystis aeruginosa

The anti-algal activity of five macrophyte extracts on the cyanobacterium Microcystis aeruginosa in Egypt was investigated in 2013. Extract activity varied according to plant type, extracting solvent and its concentration. The highest inhibitory activity was achieved with ethanol extract at a concentration of 80 mg l^?1, followed by chloroformic extracts, at 60 mg l^?1. Methanolic extracts of Eichhornia crassipes and Polygonum tomentosum inhibited growth of Microcystis aeruginosa at all concentrations. Acetonic extracts inhibited algal growth at 60 mg l^?1, except for the extract of Ceratophyllum subdemersum, which showed stimulation of M. aeruginosa growth. Eichhornia crassipes ethanolic extract exerted the most powerful inhibition by more than five-fold, 570.17%, followed by those of P. tomentosum, Saccharum spontaneum, Ceratophyllum demersum and C. subdemersum, 559.48, 553.99, 544.11 and 366.51%, respectively. Phytochemical screening for the tested plant extracts revealed the presence of biologically active substances of different concentrations, with P. tomentosum having the highest polyphenols, 1.95% of dry weight.     

Molybdate reduction by Pseudomonas sp. strain DRY2

Aims: To isolate and characterize a potent molybdenum‐reducing bacterium. Methods and Results: A minimal salt medium supplemented with 10 mmol l^?1 molybdate, glucose (1·0%, w/v) as a carbon source and ammonium sulfate (0·3%, w/v) as a nitrogen source was used in the screening process. A molybdenum‐reducing bacterium was isolated and tentatively identified as Pseudomonas sp. strain DRY2 based on carbon utilization profiles using Biolog GN plates and partial 16S rDNA molecular phylogeny. Strain DRY2 produced 2·4, 3·2 and 6·2 times more molybdenum blue compared to Serratia marcescens strain DRY6, Enterobacter cloacae strain 48 and Eschericia coli K12, respectively. Molybdate reduction was optimum at 5 mmol l^?1 phosphate. The optimum molybdate concentration that supported molybdate reduction at 5 mmol l^?1 phosphate was between 15 and 25 mmol l^?1. Molybdate reduction was optimum at 40°C and at pH 6·0. Phosphate concentrations higher than 5 mmol l^?1 strongly inhibited molybdate reduction. Inhibitors of electron transport system such as antimycin A, rotenone, sodium azide and cyanide did not inhibit the molybdenum‐reducing enzyme activity. Chromium, copper, mercury and lead inhibited the molybdenum‐reducing activity. Conclusions: A novel molybdenum‐reducing bacterium with high molybdenum reduction capacity has been isolated. Significance and Impact of the Study: Molybdenum is an emerging global pollutant that is very toxic to ruminants. The characteristics of this bacterium suggest that it would be useful in the bioremediation of molybdenum pollutant.     

Noxious floating weeds of Malaysia

After ten years of field surveys on various water bodies ranging from stagnant water ponds, pools and man-made lakes to flowing waters such as rivers, streams and canals, there is a clear evidence of four problematic weeds in Malaysia. These species are Eichhornia crassipes, Salvinia molesta, Lemna perpusilla, and Pistia stratiotes. Among these weeds, E. crassipes and S. molesta are widely distributed througout Malaysia. E. crassipes generally dominates canals and rivers although, recently, this species has spread to man-made lakes. The favourable tropical climate and conducive environmental factors help to trigger the massive growth of these weeds. The high nutrient concentrations, notably phosphate which has a soluble reactive concentration greater than 0.1 mg l^–1, initiate a high productivity. Manual control methods are generally used and several herbicides including 2,4-D and glyphosate are frequently employed to eradicate these weeds.     

Removal of Chlorpyrifos by Water Hyacinth (Eichhornia crassipes) and the Role of a Plant-Associated Bacterium

The objective of this research was to study the efficiency of water hyacinth (Eichhornia crassipes) and the role of any plant-associated bacteria in removing chlorpyrifos from water. The relative growth rate (RGR) of E. crassipes in the presence of 0.1 mg/L chlorpyrifos was not significantly different from that in its absence and only slightly decreased at concentrations of 0.5 and 1.0 mg/L by ～1.1- and ～1.2-fold, respectively, with an observed dry weight based RGR_DW for E. crassipes of 0.036–0.041 mg/g/d. The removal rate constants of chlorpyrifos in the absence of plants were low at 3.52, 2.29 and 1.84 h^?1 for concentrations of 0.1, 0.5 and 1.0 mg/L, respectively, but were some 3.89- to 4.87-fold higher in the presence of E. crassipes. Chlorpyrifos removal was markedly facilitated by the presence of a root-associated bacterium, preliminarily identified as Acinetobacter sp. strain WHA. The interaction of E. crassipes and Acinetobacter sp. strain WHA provide an efficient and ecological alternative to accelerate the removal and degradation of chlorpyrifos pollution from aquatic systems including wastewater.     

Bradyrhizobium arachidis mediated enhancement of (oxy)matrine content in the medicinal legume Sophora flavescens

Effect of rhizobial inoculation and nitrate application on the content of bioactive compounds in legume plants is an interesting aspect for interactions among microbes, plants and chemical fertilizers, as well as for cultivated practice of legumes. In this study, nitrate (0, 5 and 20 mmol l⁻¹) and Bradyrhizobium arachidis strain CCBAU 051107^T were applied, individually or in combination, to the root rhizosphere of the medicinal legume Sophora flavescens Aiton (SFA). Then the plant growth, nodulation and active ingredients including (oxy)matrine of SFA were determined and compared. Rhizobial inoculation alone significantly increased the numbers and fresh weight of root nodules. Nodulation was significantly inhibited due to nitrate (5 and 20 mmol l⁻¹). Only oxymatrine was detected in the control plants without rhizobial inoculation and nitrate supplement, while both oxymatrine and matrine were synthesized in plants treated with inoculation of B. arachidis or supplied with nitrate. The content of oxymatrine was the highest in plants inoculated solely with rhizobia and was not significantly altered by additional application of nitrate. Combinations of B. arachidis inoculation and different concentrations of nitrate did not significantly change the concentrations of (oxy)matrine in the plant. In conclusion, sole rhizobial inoculation was the best approach to increase the contents of key active ingredients oxymatrine and matrine in the medicinal legume SFA.     

Impact of invasive apple snails in Hong Kong on wetland macrophytes,nutrients, phytoplankton and filamentous algae

1. Grazing by invasive species can affect many aspects of an aquatic system, but most studies have focused on the direct effects on plants. We conducted mesocosm and laboratory experiments to examine the impact of the invasive apple snail Pomacea canaliculata on macrophytes, filamentous algae, nutrients and phytoplankton. 2. In a freshwater pond, we confined 500 g of Myriophyllum aquaticum or Eichhornia crassipes with 0, 2, 4 or 8 apple snails in 1 m × 1 m × 1 m enclosures for approximately 1 month. Apple snails grazed heavily on both species of macrophytes, with higher overall weight losses at higher snail densities. The damage patterns differed between the two macrophytes. In M. aquaticum, both leaves and stems suffered from substantial herbivory, whereas in E. crassipes, only the roots suffered significant weight reduction. 3. In addition to grazing on macrophytes, apple snails appeared to have controlled the growth of filamentous algae, as these did not develop in the snail treatments. The ability of P. canaliculata to control filamentous algae was supported by a laboratory experiment where the consumption was as high as 0.25 g g⁻¹ snail DW d⁻¹. Because of a lack of native herbivorous snails in the pond, the growth of filamentous algae (mainly Spirogyra sp.) reached 80.3 g m⁻², forming a spongy pond scum in the no‐apple snail control. Together with previous reports that apple snails could eat the juveniles and eggs of other freshwater snails, our results indicated that P. canaliculata could have out‐competed native herbivorous snails from the pond by predation on their juveniles or eggs. Alternatively, P. canaliculata might have out‐competed them by monopolisation of food resources. 4. Nitrogen and phosphorous concentrations remained low throughout both experiments and were not correlated with apple snail density. The treatment effects on chlorophyll a (Chl a) and phytoplankton composition varied in the two experiments. In the M. aquaticum experiment, with increasing snail density, Chl a increased, and the phytoplankton community became dominated by Cryptophyceae. In the E. crassipes experiment, Chl a level was independent of snail density, but with increasing snail density, the phytoplankton community became co‐dominated by Cryptophyceae, Chlorophyceae and Bacillariophyceae. 5. Given the multiple effects of P. canaliculata on wetland biodiversity and function, management strategies should be developed to prevent its further spread. In invaded wetlands, strategies should be developed to eradicate the apple snail and re‐introduce native snails which can control the development of filamentous algae.     

Conversion of xylose to ethanol by a novel phenol-tolerant strain of Enterobacteriaceae isolated from olive mill wastewater

A xylose-fermenting bacterium of the family Enterobacteriaceae was isolated from olive mill wastewater. It converted xylose to ethanol with a yield of 0.19 g ethanol g^–1 xylose. Although phenolic compounds normally inhibit pentose-utilizing microorganisms, this isolate was tolerant to phenol. Both the yield and the productivity of xylose fermentation decreased by 30% when phenol was added at a final concentration of 0.8 g phenol l^–1. Xylose (23 g l^–1) was totally fermented to ethanol (4.3 g l^–1) within 48 h in the absence of phenol; however, in the presence of 0.8 g phenol l^–1, only 3.3 g ethanol l^–1 was obtained from the same starting concentration of xylose after 70 h.     

Characterization of Copper-Resistant Rhizosphere Bacteria from <Emphasis Type="Italic">Avena sativa</Emphasis> and <Emphasis Type="Italic">Plantago lanceolata</Emphasis> for Copper Bioreduction and Biosorption

Copper is a toxic heavy metal widely used to microbial control especially in agriculture. Consequently, high concentrations of copper residues remain in soils selecting copper-resistant organisms. In vineyards, copper is routinely used for fungi control. This work was undertaken to study copper resistance by rhizosphere microorganisms from two plants (Avena sativa L. and Plantago lanceolata L.) common in vineyard soils. Eleven rhizosphere microorganisms were isolated, and four displayed high resistance to copper. The isolates were identified by 16S rRNA gene sequence analysis as Pseudomonas putida (A1), Stenotrophomonas maltophilia (A2) and Acinetobacter sp. (A6), isolated from Avena sativa rhizosphere, and Acinetobacter sp. (T5), isolated from Plantago lanceolata rhizosphere. The isolates displayed high copper resistance in the temperature range from 25°C to 35°C and pH in the range from 5.0 to 9.0. Pseudomonas putida A1 resisted as much as 1,000 mg L⁻¹ of copper. The isolates showed similar behavior on copper removal from liquid medium, with a bioremoval rate of 30% at 500 mg L⁻¹ after 24 h of growth. Speciation of copper revealed high copper biotransformation, reducing Cu(II) to Cu(I), capacity. Results indicate that our isolates are potential agents for copper bioremoval and bacterial stimulation of copper biosorption by Avena sativa and Plantago lanceolata.     

Toxicity of common biocides used in aquaculture to embryos and larvae of Brachymystax tsinlingensis Li

Brachymystax tsinlingensis Li is a threatened fish species endemic to China. With the problems of environmental factors and seeding breeding diseases, it is important to further improve the efficiency of seeding breeding and the basis of resource protection. This study investigated the acute toxicity of copper, zinc and methylene blue (MB) on hatching, survival, morphology, heart rate (HR) and stress behaviour of B. tsinlingensis. Eggs (diameter: 3.86 ± 0.07 mm, weight: 0.032 ± 0.004 g) of B. tsinlingensis were selected randomly from artificial propagation and developed from eye-pigmentation-stage embryos to yolk-sac stage larvae (length: 12.40 ± 0.02 mm, weight: 0.03 ± 0.001 g) and exposed to different concentrations of Cu, Zn and MB for 144 h in a series of semi-static toxicity tests. The acute toxicity tests indicated that the 96-h median lethal concentration (LC₅₀) values of the embryos and larvae were 1.71 and 0.22 mg l⁻¹ for copper and 2.57 and 2.72 mg l⁻¹ for zinc, respectively, whereas the MB LC₅₀ after 144-h exposure for embryos and larvae were 67.88 and 17.81 mg l⁻¹, respectively. The safe concentrations of copper, zinc and MB were 0.17, 0.77 and 6.79 mg l⁻¹ for embryos and 0.03, 0.03 and 1.78 mg l⁻¹ for larvae, respectively. Copper, zinc and MB treatments with concentrations greater than 1.60, 2.00 and 60.00 mg l⁻¹, respectively, led to a significantly low hatching rate and significantly high embryo mortality (P < 0.05), and copper and MB treatments with concentrations greater than 0.2 and 20 mg l⁻¹ led to significantly high larvae mortality (P < 0.05). Exposure to copper, zinc and MB resulted in developmental defects, including spinal curvature, tail deformity, vascular system anomalies and discolouration. Moreover, copper exposure significantly reduced the HR of larvae (P < 0.05). The embryos exhibited an obvious change in behaviour, converting from the normal behaviour of emerging from the membrane head first to emerging tail first, with probabilities of 34.82%, 14.81% and 49.07% under copper, zinc and MB treatments, respectively. The results demonstrated that the sensitivity of yolk-sac larvae to copper and MB was significantly higher than that of embryos (P < 0.05) and that B. tsinlingensis embryos or larvae might be more resistant to copper, zinc and MB than other members of the Salmonidae family, which benefits their resource protection and restoration.     

Use of enzymatic cell wall degradation for improvement of protein extraction from Chondrus crispus,Gracilaria verrucosa and Palmaria palmata

The effect of polysaccharidases (κ-carrageenase, β-agarase, xylanase, cellulase) on the protein extraction from three rhodophytes has been studied. The kinetic parameters (apparent V _m, apparent K _m) and the optimum activity conditions (pH, temperature) of each enzyme were determined by using pure substrates. All the tested enzymes possess Michaelis Menten mechanism with estimated substrate saturating concentrations of 8 000 mg l⁻¹(carrageenan) for κ-carrageenase, 8 000 mg l⁻¹ (agar) for β-agarase, 5000 mg l⁻¹ (xylane) for β-xylanase and 6 000 mg l⁻¹ (carboxymethylcellulose) for cellulase. The optimum activity conditions are pH 6.5–6.8 at 45°C for carrageenase, pH 6–6.5 at 55°C for agarase, pH 5 at 55°C for xylanase and pH 3.8 at 50°C for cellulose. Different alga/enzymes couples (κ-carrageenase/Chondrus crispus, β-agarase/Gracilaria verrucosa, β-xylanase/Palmaria palmata) were tested under the optimum activity conditions. Alga/cellulase + specific enzyme (e.g. Chondrus crispus/carrageenase + cellulase) systems were also studied at the optimum activity conditions of a specific enzyme (e.g. carageenase). The use of the only cellulose was also tested on each alga. Except for Palmaria palmata, the highest protein yields were observed with the procedures using cellulase coupled with carrageenase or agarase for an incubation period limited to 2 h. The Chondrus crispus/carrageenase + cellulose and Gracilaria verrucosa/agarase + cellulase systems gave ten-fold and three-fold improvements, respectively, in protein extraction yield as compared to the enzyme-free blank procedure. The combined action of xylanase and cellulose on protein extraction from Palmaria palmata does not significantly improve protein yield. The best overall protein yield for P. palmata is for P. palmata/xylanase with a 14-h incubation time. This study shows the interest in the use of a polysaccharidase mixture for improving protein extractibility from certain rhodophytes. This biotechnology approach, adapted from procedures for protoplast production or enzymatic liquefaction of higher plants, could be tested as an alternative method to obtain proteins from seaweeds of nutritional interest.     

Influence of <Emphasis Type="Italic">Potamogeton crispus</Emphasis> growth on nutrients in the sediment and water of Lake Tangxunhu

An incubation experiment was performed on Potamogeton crispus (P. crispus) using sediment collected from Lake Tangxunhu in the center of China, in order to determine the effects of plant growth on Fe, Si, Cu, Zn, Mn, Mg, P, and Ca concentrations in the sediments and overlying waters. After 3 months of incubation, Ca, Mg, and Si concentrations in the water column were significantly lower, and P and Cu concentrations were significantly higher than in unplanted controls. The effect of P. crispus growth on sediment pore waters and water-extractable elements varied. Concentrations of Ca, Mg, Si, Fe, Cu, and Zn were significantly higher, and P was significantly lower, than in pore waters of the control. Water-extracted concentrations of Fe, Mg, and Si in the sediments were lower, and P was higher, than in the control. Presence of P. crispus generally enhanced concentration gradients of elements between pore waters and overlying waters but not for P. The growth of P. crispus was associated with an increase in water pH and formation of root plaques, resulting in complex effects on the sediment nutritional status. Handling editor: S. M. Thomaz     

Concentration dependent growth/non-growth linked kinetics of endosulfan biodegradation by <Emphasis Type="Italic">Pseudomonas aeruginosa</Emphasis>

The rates of biodegradation of endosulfan by P. aeruginosa were determined with different initial endosulfan concentrations (10, 50, 100, 150, 200 and 250 mg l⁻¹) and different growth linked kinetic models were fitted at these concentrations. At 10 mg endosulfan l⁻¹, Monod no growth model was well fitted. Monod with growth model described the biodegradation pattern at an initial concentration of 50, 100 and 150 mg endosulfan l⁻¹. Significant increases of P. aeruginosa MN2B14 density in broth culture during incubation further support this result. Conversely, zero order kinetic model was well fitted into the biodegradation data if initial endosulfan concentration was ≥200 mg endosulfan l⁻¹. The kinetics of endosulfan biodegradation by P. aeruginosa MN2B14 in liquid broth was highly dependent upon its initial concentration. The results of this study could be employed for predicting the persistence of endosulfan in water environment containing P. aeruginosa as an endosulfan degrading bacterium.     

Do Larvae and Ovipositing Chironomus riparius (Diptera: Chironomidae) Females Avoid Copper-Contaminated Environments?

Studies on the avoidance behavior of aquatic organisms to contaminants have confirmed that such behavior can be relevant in field situations. However, almost all toxicity tests involve the forced exposure of organisms to toxicants. In particular, despite the importance of Chironomus riparius Meigen larvae in sediment toxicity testing, only a few studies on avoidance behavior have been performed. This study investigated the ability of different life stages of C. riparius, including ovipositing females, first-, second-, and fourth-instar larvae, to avoid copper-contaminated environments. Ovipositing females were given a choice between a control and copper solution (1.3 mg Cu l^{? 1}). First-instar larvae were provided with a choice between a control and a copper (2.0 mg Cu l^{? 1})-spiked sediment. Both second- and fourth-instars were exposed to a copper gradient (0.38–3.4 mg Cu l^{? 1}) in a flow-through system. None of the life stages avoided copper, even though the highest concentrations caused lethal effects on midges. The avoidance behavior of C. riparius is not a sensitive endpoint to assess copper sublethal toxicity.     

Production of high ethanol concentrations from glucose using a vertical rotating immobilized cell reactor of the bacterium zymomonas mobilis

Long-term continuous ethanol production of up to 80 g.l¹ with a volumetric ethanol productivity of 63 g. l^?1. h^?1 was maintained for more than 72 days using a Vertical Rotating Immobilized Cell Reactor of the bacterium Z. mobilis. Continuous production of higher ethanol concentration was unsuccessful due to an inhibition of cell growth by long exposure to high ethanol concentrations. However, ethanol concentration as high as 120g. l^?1 and volumetric ethanol productivity of 13g. l^?1. h^?1 were achieved in a repeated-batch fermentation system using the same bioreactor. By a simple washing operation at the end of each run, immobilized biomass could be effectively regenerated and used to carry out more than 10 successive fermentation cycles.     

Selection of Chickpea-Rhizosphere-Competent Pseudomonas fluorescens NBRI1303 Antagonistic to Fusarium oxysporum f. sp. ciceri,Rhizoctonia bataticola and Pythium sp.

A procedure that consumes less screening time was developed for screening chickpea rhizosphere-competent bacteria for suppression of the chickpea pathogenic fungi Fusarium oxysporum f. sp. ciceri, Rhizoctonia bataticola and Pythium sp. Of the 478 bacteria obtained by random selection of the predominant, morphologically distinct colonies, 386 strains that effectively colonize chickpea roots could be divided broadly into three different groups. The first group consisted of 44 good chickpea rhizosphere colonizers with 10⁷ to 10⁸ colony-forming units (CFU)/g root; the second group consisted of 253 medium chickpea rhizosphere colonizers with 10⁴ to 10⁶ CFU/g root; and the third group consisted of 89 poor chickpea rhizosphere colonizers with 10⁰ (nondetectable) to 10³ CFU/g root. Forty-four Rif^r strains from the first group of good chickpea rhizosphere colonizers were further screened for their in vitro biocontrol activity against F. oxysporum f. sp. ciceri, R. bataticola, and Pythium sp. One bacterial strain was selected for further work because of its unique ability to inhibit all three fungi and its good chickpea rhizosphere colonization ability. This is the first report of a single biocontrol bacterium active against three most devastating pathogenic fungi of chickpea. In a greenhouse test, chickpea seed bacterization with P. fluorescens NBRI1303 increased the germination of seedlings by 25%, reduced the number of diseased plants by 45%, compared with nonbacterized controls. Increases in seedling dry weight, shoot length, and root length ranged from 16% to 18%. Significant growth increases in shoot length, dry weight, and grain yield, averaging 11.59%, 17.58%, and 22.61% respectively above untreated controls, were attained in field trials in Agra and Jhansi. A rifampicin-resistant mutant P. fluorescens NBRI1303R of the P. fluorescens NBRI1303, used to monitor chickpea root colonization, confirmed the rapid and aggressive colonization by the bacterium, making it a potential biocontrol agent against chickpea phytopathogenic fungi. The results, demonstrating an increase in the efficiency of screening and detection of plant beneficial strains, should greatly benefit future studies. Received: 23 December 1996 / Accepted: 28 January 1997     

Factors affecting accumulation and loss of zinc by the aquatic moss Rhynchostegium riparioides (Hedw.) C. Jens.

Reciprocal transplants of the moss Rhynchostegium riparioides (Herw.) C. Jens. between populations from streams with high (0.27 mg l⁻¹) and low (0.05 mg l⁻¹) concentrations of Zn showed that Zn uptake over the first 12 h was twice as fast as loss and reached an asymptotic value sooner. However, Zn accumulation was lower in a nutrient-rich (high nitrate and phosphate) than a nutrient-poor stream (4.5 vs. 7.0 mg g⁻¹). Shoots from a high-Zn site (0.70 mg l⁻¹) contained increased Zn concentrations on passing away from the apex and higher concentrations in leaves than stems (6.5 vs. 3.3 mg g⁻¹). Shoots freshly exposed to 1.0 mg l⁻¹ Zn in the laboratory showed similar Zn concentrations at different positions along the stem after exposure for 2 h, but by 24 h the gradient was similar to that found in field material. Ca, Mg, Mn and chelating agents (EDTA, humic acids) all decreased Zn accumulation in the laboratory, but neither nitrate nor phosphate over concentration ranges of two orders of magnitude had any influence.A greater proportion of Zn accumulated over a 24-h period was lost than that accumulated over a 10-day period (66 vs. 45%), even though the total Zn was similar (ca. 3.8 mg g⁻¹) at the beginning of the loss experiments. Studies with NiCl₂ as an eluting agent indicate that this and other observations may be interpreted by assuming that an ‘exchangeable’ Zn fraction becomes converted with time to a ‘residual’ Zn fraction.     

Effects of Pb<Superscript>2+</Superscript> on the active oxygen-scavenging enzyme activities and ultrastructure in <Emphasis Type="Italic">Potamogeton crispus</Emphasis> leaves

The effects of various concentrations of Pb²⁺ on the antioxidant enzyme activities and the ultrastructure in Potamogeton crispus leaves were studied. Peroxidase (POD) activity and malondialdehyde (MDA) content peaks were observed with an increase in Pb²⁺ concentration, whereas superoxide dismutase (SOD) and catalase (CAT) activities decreased firstly and then rose. Meantime, the chlorophyll content declined with increasing Pb²⁺ concentration. Simultaneously, high concentrations of Pb²⁺ aggravated ultrastructural damage to the leaf cells including swelling of chloroplasts, disruption and disappearance of chloroplast envelopes; swelling of mitochondrial cristae, deformation and vacuolation of mitochondria; condensation of chromatin, dispersion of nucleoli, and disruption of nuclear membrane. Changes in antioxidant enzyme activities and damage to fine structure are the results of lead-induced ROS accumulation. The estimated lethal concentration to P. crispus ranged from 10 to 15 mg/l lead. Published in Russian in Fiziologiya Rastenii, 2007, Vol. 54, No. 3, pp. 469–474. The text was submitted by the authors in English.     

Invasive crayfish in Europe: the impact of Procambarus clarkii on the littoral community of a Mediterranean lake

1. Despite the growing number of non‐indigenous crayfish species introduced worldwide, little scientific attention has been given to their effects on the recipient communities. Here, we quantified the impact of adult red swamp crayfish (Procambarus clarkii) on key components of the littoral community of a mesotrophic lake in central Italy. We used two densities of crayfish plus a no‐crayfish control, and two complementary methods –in situ enclosures and a laboratory study. 2. Both experiments showed that P. clarkii strongly affects the community even at a low density (4 m⁻²), although a high crayfish density (8 m⁻²) showed a more pronounced impact in a shorter time. 3. In enclosures, P. clarkii quickly consumed the pond snail Haitia acuta, notwithstanding its anti‐predator behaviour, but not the mosquitofish Gambusia affinis. The biomass of the hydrophytes Nymphoides peltata and Potamogeton spp. was strongly reduced by crayfish grazing, coupled with their non‐consumptive plant clipping and uprooting, which were particularly intense in the case of Potamogeton crispus. In contrast, Utricularia australis was avoided by P. clarkii, even when other resources were exhausted. 4. The introduction of P. clarkii could reduce biodiversity and increase biotic homogenisation in a short time.     

Multi-modular engineering of Saccharomyces cerevisiae for high-titre production of tyrosol and salidroside

Tyrosol and its glycosylated product salidroside are important ingredients in pharmaceuticals, nutraceuticals and cosmetics. Despite the ability of Saccharomyces cerevisiae to naturally synthesize tyrosol, high yield from de novo synthesis remains a challenge. Here, we used metabolic engineering strategies to construct S. cerevisiae strains for high-level production of tyrosol and salidroside from glucose. First, tyrosol production was unlocked from feedback inhibition. Then, transketolase and ribose-5-phosphate ketol-isomerase were overexpressed to balance the supply of precursors. Next, chorismate synthase and chorismate mutase were overexpressed to maximize the aromatic amino acid flux towards tyrosol synthesis. Finally, the competing pathway was knocked out to further direct the carbon flux into tyrosol synthesis. Through a combination of these interventions, tyrosol titres reached 702.30 ± 0.41 mg l⁻¹ in shake flasks, which were approximately 26-fold greater than that of the WT strain. RrU8GT33 from Rhodiola rosea was also applied to cells and maximized salidroside production from tyrosol in S. cerevisiae. Salidroside titres of 1575.45 ± 19.35 mg l⁻¹ were accomplished in shake flasks. Furthermore, titres of 9.90 ± 0.06 g l⁻¹ of tyrosol and 26.55 ± 0.43 g l⁻¹ of salidroside were achieved in 5 l bioreactors, both are the highest titres reported to date. The synergistic engineering strategies presented in this study could be further applied to increase the production of high value-added aromatic compounds derived from the aromatic amino acid biosynthesis pathway in S. cerevisiae.