Biodegradation and biosorption of tetracycline and tylosin antibiotics in activated sludge system

The aim of this study was to determine the fate of veterinary antibiotics entering biological treatment process. Due to the prevalence of their respective antibiotic family usage in livestock, tetracycline and tylosin were selected. Using modified Sturm test (OECD 301-B), their biodegradation were compared to that of a referent pollutant, sodium benzoate, well-known for its high biodegradability. Biodegradation rates were ?28 and ?35% for tetracycline and 4 and ?5% for tylosin showing an absence of biodegradability. OECD 301-B inhibition tests showed a potential toxicity of both molecules on activated sludge inoculum derived from membrane bioreactor. Tetracycline presented good adsorbability while tylosin remained mostly present in the soluble phase. The Langmuir maximum adsorption capacity (C_s,max) was found to be 72 and 7.7 mg g^?1 for tetracycline and tylosin, respectively. Adsorption was therefore the most favourable fate for tetracycline entering a biological process. Conclusions on tylosin case were more controversial.     

Microbial processes and bacterial populations associated to anaerobic treatment of sulfate-rich wastewater

A pilot-scale (1.2 m³) anaerobic sequencing batch biofilm reactor (ASBBR) containing mineral coal for biomass attachment was fed with sulfate-rich wastewater at increasing sulfate concentrations. Ethanol was used as the main organic source. Tested COD/sulfate ratios were of 1.8 and 1.5 for sulfate loading rates of 0.65–1.90 kgSO₄²⁻/cycle (48 h-cycle) or of 1.0 in the trial with 3.0 gSO₄²⁻ l⁻¹. Sulfate removal efficiencies observed in all trials were as high as 99%. Molecular inventories indicated a shift on the microbial composition and a decrease on species diversity with the increase of sulfate concentration. Beta-proteobacteria species affiliated with Aminomonas spp. and Thermanaerovibrio spp. predominated at 1.0 gSO₄²⁻ l⁻¹. At higher sulfate concentrations the predominant bacterial group was Delta-proteobacteria mainly Desulfovibrio spp. and Desulfomicrobium spp. at 2.0 gSO₄²⁻ l⁻¹, whereas Desulfurella spp. and Coprothermobacter spp. predominated at 3.0 gSO₄²⁻ l⁻¹. These organisms have been commonly associated with sulfate reduction producing acetate, sulfide and sulfur. Methanogenic archaea (Methanosaeta spp.) was found at 1.0 and 2.0 gSO₄²⁻ l⁻¹. Additionally, a simplified mathematical model was used to infer on metabolic pathways of the biomass involved in sulfate reduction.     

Enzymatic hydrolysis of corncob and ethanol production from cellulosic hydrolysate

 Enzymatic hydrolysis of corncob and ethanol fermentation from cellulosic hydrolysate were investigated. After corncob was pretreated by 1% H₂SO₄ at 108 °C for 3 h, the cellulosic residue was hydrolyzed by cellulase from Trichoderma reesei ZU-02 and the hydrolysis yield was 67.5%. Poor cellobiase activity in T. reesei cellulase restricted the conversion of cellobiose to glucose, and the accumulation of cellobiose caused severe feedback inhibition to the activities of β-1,4-endoglucanase and β-1,4-exoglucanase in cellulase system. Supplementing cellobiase from Aspergillus niger ZU-07 greatly reduced the inhibitory effect caused by cellobiose, and the hydrolysis yield was improved to 83.9% with enhanced cellobiase activity of 6.5 CBU g⁻¹ substrate. Fed-batch hydrolysis process was started with a batch hydrolysis containing 100 g l⁻¹ substrate, with cellulosic residue added at 6 and 12 h twice to get a final substrate concentration of 200 g l⁻¹. After 60 h of reaction, the reducing sugar concentration reached 116.3 g l⁻¹ with a hydrolysis yield of 79.5%. Further fermentation of cellulosic hydrolysate containing 95.3 g l⁻¹ glucose was performed using Saccharomyces cerevisiae 316, and 45.7 g l⁻¹ ethanol was obtained within 18 h. The research results are meaningful in fuel ethanol production from agricultural residue instead of grain starch.     

Naphthalene and biphenyl oxidation by two marine Pseudomonas strains isolated from Venice Lagoon sediment

A sediment sample from Venice Lagoon was found to be contaminated with 475 mg Kg⁻¹ polycyclic aromatic hydrocarbons (PAHs). Naphthalene was the principal pollutant at 26% of total PAHs. Two strains of Pseudomonas SN1 and SB1 were isolated from sediment amended with 2% naphthalene. 16S rRNA gene sequence analysis indicated that the two strains have about 99% nucleotide identity with strains of the genus Pseudomonas, and are very close to Pseudomonas stutzeri. Their metabolic profiles showed significant nutritional differences, the most significant of which was that SN1 grows in marine mineral medium spiked with naphthalene and SB1 grows with biphenyl as sole carbon and energy sources. Pseudomonas sp. SN1 had a doubling time of 3.1 h with 2% naphthalene and SB1 had a doubling time of 19.5 h with 2% biphenyl. Strain SN1 oxidised naphthalene at 564±32 mg O₂ l⁻¹ d⁻¹ and SB1 oxidised biphenyl at 426±25 mg O₂ l⁻¹ d⁻¹ in respirometry reaction vessels under controlled conditions. Screening of the two strains for dioxygenase genes involved in the first step of the two hydrocarbon degradation pathways, by polymerase chain reaction, showed naphthalene dioxygenase in SN1 and biphenyl dioxygenase in SB1. The strains each have a different catechol 2,3-dioxygenase responsible for cleavage of the aromatic ring.     

Evaluation of distant carbon sources in biosurfactant production by a gamma ray-induced Pseudomonas putida mutant

Pseudomonas putida 33 wild strain, subjected to gamma ray mutagenesis and designated as P. putida 300-B mutant was used as microbial rhamnolipid-producer by using distant carbon sources (viz. hydrocarbons, waste frying oils ‘WFOs’, vegetable oil refinery wastes and molasses) in the minimal media under shake flask conditions. The behavior of glucose as co-substrate and growth initiator was examined. The 300-B mutant strain showed its ability to grow on all the substrates tested and produced rhamnolipid surfactants to different extents however; soybean and corn WFOs were observed to be preferred carbon sources followed by kerosene and paraffin oils, respectively. The best cell biomass (3.5 g l⁻¹) and rhamnolipids yield (4.1 g l⁻¹) were obtained with soybean WFO as carbon source and glucose as growth initiator under fed-batch cultivation showing an optimum specific growth rate (μ) of 0.272 h⁻¹, specific product yield (q_p) of 0.318 g g⁻¹ h and volumetric productivity (P_V) of 0.024 g l⁻¹ h. The critical micelle concentration of its culture supernatant was observed to be 91 mg rhamnolipids l⁻¹ and surface tension as 31.2 mN m⁻¹.     

Effects of feed sugar concentration on continuous ethanol fermentation of cheese whey powder solution (CWP)

Cheese whey powder (CWP) solution with different CWP or sugar concentrations was fermented to ethanol in a continuous fermenter using pure culture of Kluyveromyces marxianus (DSMZ 7239). Sugar concentration of the feed CWP solution varied between 55 and 200 g l⁻¹ while the hydraulic residence time (HRT) was kept constant at 54 h. Ethanol formation, sugar utilization and biomass formation were investigated as functions of the feed sugar concentration. Percent sugar utilization and biomass concentrations decreased and the effluent sugar concentration increased with increasing feed sugar concentrations especially for the feed sugar contents above 100 g l⁻¹. Ethanol concentration and productivity (DP) increased with increasing feed sugar up to 100 g l⁻¹ and then decreased with further increases in the feed sugar content. The highest ethanol concentration (3.7%, v v⁻¹) and productivity (0.54 gE l⁻¹ h⁻¹) were obtained with the feed sugar content of 100 g l⁻¹ or 125 g l⁻¹. The ethanol yield coefficient (Y_P/S) was also maximum (0.49 gE gS⁻¹) when the feed sugar was between 100 and 125 g l⁻¹. The growth yield coefficient (Y_X/S) decreased steadily from 0.123 to 0.063 gX gS⁻¹ when the feed sugar increased from 55 to 200 g l⁻¹ due to adverse effects of high sugar contents on yeast growth. The optimal feed sugar concentration maximizing the ethanol productivity and sugar utilization was between 100 and 125 g l⁻¹ under the specified experimental conditions.     

Kinetics parameter estimation for the binding process of salicylic acid to human serum albumin (HSA) with capacitive sensing technique

A novel method for real-time investigating the binding interaction between human serum albumin (HSA) and salicylic acid with capacitive sensing technique was successfully proposed. HSA was immobilized on the surface of a gold electrode modified with an insulating poly (o-phenylenediamine) (o-PD) film and colloid Au nanoparticles layers. The bioactivity of HSA was remained and major binding sites were available because of the excellent biocompatibility of gold nanoparticles. The capacitance and interfacial electron resistance of the sensor were altered, owing to the binding of HSA to salicylic acid. The time courses of the capacitance change were acquired with capacitive sensing technique during the binding process. Based on the capacitance response curves with time, the response model for the binding was derived in theory and the corresponding regression parameters were determined by fitting the real-time experimental data to the model. The binding and the dissociation rate constants (k₁ and k_− 1) were estimated to be 54.8 (mol l^− 1)^− 1 s^− 1 and 2.9 × 10^− 3 s^− 1, respectively. And the binding equilibrium constant (K_a) was calculated to be 1.89 × 10⁴ (mol l^− 1)^− 1.     

Signal transducer and oxidative stress mediated modulation of phenylpropanoid pathway to enhance rosmarinic acid biosynthesis in fungi elicited whole plant culture of Solenostemon scutellarioides

This study aimed to improve rosmarinic acid (RA) production in the whole plant culture of Solenostemon scutellarioides through elicitation with phytopathogenic fungi. Amongst selected fungi, Aternaria alternata caused significant elevation (p < 0.05–0.01) in RA accumulation (∼1.3–1.6-fold) between 25 and 100 μg l⁻¹. However, elicitation at the dose of 50 μg l⁻¹ has been found to be most effective and intracellular RA content reached almost ∼1.6-fold (p < 0.01) higher in day 7. Therefore, A. alternata (50 μg l⁻¹) was selected for mechanism evaluation. A significant elevation of intercellular jasmonic acid was observed up to day 6 after elicitation with A. alternata (50 μg l⁻¹). A significant increase in tissue H₂O₂ and lipid peroxidation coupled with depletion of antioxidant enzymes superoxide dismutase and catalase indicated augmented oxidative stress associated with biotic interaction. Preceding the elicitor-induced RA accumulation, a notable alteration in the specific activities of biosynthetic enzymes namely PAL and TAT was recorded, while, no significant change in the activities of RAS was observed. HPPR activity was slightly improved in elicited plant. Therefore, it could be concluded that A. alternata elicited the biosynthesis of rosmarinic acid via signal transduction through jasmonic acid coupled with elicitor induced oxidative stress and associated mechanism.     

Functional consortium for hydrogen production from cellobiose: Concentration-to-extinction approach

A functional bacterial consortium that can effectively hydrolyze cellobiose and produce bio-hydrogen was isolated by a concentration-to-extinction approach. The sludge from a cattle feedlot manure composting plant was incubated with 2.5–20 g l^?1 cellobiose at 35 °C and pH 6.0. The microbial diversity of serially concentrated suspensions significantly decreased following increasing cellobiose concentration, finally leaving only two viable strains, Clostridium butyricum strain W4 and Enterococcus saccharolyticus strain. This consortium has a maximum specific hydrogen production rate of 2.19 mol H₂ mol hexose^?1 at 5 g l^?1 cellobiose. The metabolic pathways shifted from ethanol-type to acetate-butyrate type as cellobiose concentration increased from 2.5 to >7 g l^?1. The concentration-to-extinction approach is effective for isolating functional consortium from natural microflora. In this case the functional strains of interest are more tolerant to the increased loadings of substrates than the non-functional strains.     

Multiple regeneration pathways in Spathoglottis plicata Blume — A study in vitro

Asymbiotic germination of immature seeds (embryos), and mature seeds and micropropagation of Spathoglottis plicata were described. Effects of three nutrition media namely, Murashige & Skoog (MS); Phytamax (PM); and Phyto-Technology orchid seed sowing medium (P₇₂₃), two carbon sources such as glucose and sucrose at 2–3% (w/v), two plant growth regulators such as 6-benzylaminopurine (BAP; 0.5–3.0 mg l^− 1) and α-naphthalene acetic acid (NAA; 0.5–2.0 mg l^− 1) and peptone (2.0 g l^− 1) were examined on seed germination, early protocorm development and micropropagation. The maximum germination of mature seeds (95%) was recorded in PM medium supplemented with 2% (w/v) sucrose + 2.0 g l^− 1 peptone. For germination of embryos P₇₂₃ medium supplemented with 1.0 mg l^− 1 BAP proved best. Multiple shoot buds or protocorm-like bodies (PLBs) were produced from stem segments of in vitro raised seedlings. Both direct organogenesis and embryogenesis were observed and the morphogenetic response was initiated by different concentrations and combinations of PGRs. The optimum PGR combination for maximal PLB regeneration was 1.0 mg l^− 1 NAA + 2.5 mg l^− 1 BAP, while 1.0 mg l^− 1 NAA + 1.0 mg l^− 1 BAP for shoot bud development. Strong and stout root system was induced in half strength PM medium supplemented with 0.5 mg l^− 1 IAA. The well-rooted plantlets were transferred to pots containing a potting mixture composed of saw dust, coconut coir, humus, and coal pieces at 1:1:1:2 (w/w) with 80% survival in outside environment and flowered after two years of transfer.     

Ornamental characters,ion accumulation and water status in Arbutus unedo seedlings irrigated with saline water and subsequent relief and transplanting

Arbutus unedo seedlings were grown in a greenhouse and submitted to three irrigation treatments (salinity period) using solutions with an EC of 0.85 dS m^?1 (control treatment), 5.45 dS m^?1 (S1) and 9.45 dS m^?1 (S2). After 16 weeks, growth and ornamental characters, leaf water potentials, gas exchange and ion concentrations were determined. After the salinity period, plants were exposed to a relief period for 1 month, whereby half of the plants were transplanted to field conditions and the other half into 24 cm diameter plastic pots. Salinity induced a significant decrease in shoot biomass and leaf area but root/shoot ratio was increased. Plant height was significantly inhibited by salinity. The ornamental characters were affected in the treated plants, with symptoms of salt injury, such as burning of leaf margin. Leaf water potentials decreased with increasing salinity, more significantly at predawn than at midday. The relationship between net photosynthesis (P_n) and leaf conductance (g_l) was linear for all treatments and the same values of P_n are associated with lower values of g_l for the saline treatments than for control treatment. The concentration of Cl^? in leaves increased with increasing salinity and was higher than the corresponding concentration of Na⁺. Na⁺ and Cl^? contents were higher in the leaves than in the roots in both saline treatments. The K⁺ and Ca²⁺ levels were lower in the treated plants than in control plants and applied salinity reduced the K⁺/Na⁺ ratio in leaves, stems and roots, the decrease being much greater for leaves than for roots. The Ca²⁺/Na⁺ ratio fell with salinity in all parts of the plants. At the end of the relief period leaf water potentials were recovered mainly in field conditions. S2 treatment showed lower values of P_n and g_l than control and S1 treatments in pot conditions and in field conditions S1 showed the lowest values for P_n and g_l.     

Enhancement of polysaccharide production in suspension cultures of protocorm-like bodies from Dendrobium huoshanense by optimization of medium compositions and feeding of sucrose

A strategy that optimization of medium compositions for maximum biomass followed by feeding of sucrose for maximum polysaccharide synthesis was developed for enhancing polysaccharide production in suspension culture of protocorm-like bodies (PLBs) of Dendrobium huoshanense C.Z. Tang et S.J. Cheng. In growth stage, the original half-strength MS medium was optimized with carbon sources, nitrogen sources and metal ion combinations. The effects of different carbon sources on PLBs growth were remarkable and sucrose at 35 g l⁻¹ was the most suitable. Sole nitrate nitrogen of 30 mmol l⁻¹ was the best for PLBs growth. Metal ions (Ca²⁺, Fe²⁺, Mn²⁺ and Zn²⁺) showed different influences on PLBs growth. The optimal concentration of Ca²⁺, Fe²⁺, Mn²⁺ and Zn²⁺ was 4.5 mmol l⁻¹, 0.1 mmol l⁻¹, 0.5 mmol l⁻¹ and 0.06 mmol l⁻¹, respectively. In the optimized medium (sucrose, nitrate, Ca²⁺, Fe²⁺, Mn²⁺ and Zn²⁺ concentration as described above, the other component concentration seen in half-strength MS), 33.9 g DW l⁻¹ PLBs were harvested after 30 days of culture and biomass increase was improved 245% as compared with that in the original medium. In production stage, polysaccharide synthesis was significantly improved by the feeding sucrose. The maximum polysaccharide production (22 g l⁻¹) was obtained in the case of 50 g l⁻¹ sucrose feeding at day 30 of culture, which was about 109-fold higher than that in the original medium without feeding of sucrose.     

Scale-up of micro-aerobic 1,3-propanediol production with Klebsiella pneumonia CGMCC 1.6366

The conversion of glycerol to 1,3-propanediol (1,3-PD) using Klebsiella pneumoniae CGMCC 1.6366 under aerobic condition was scaled up from scale 5 to 50,000 l in series. Several parameters including power input P/V_l, agitation rate n, impeller tip speed nD, superficial gas velocity u_s, and Re_s were investigated as the criteria for scaling up. Impeller tip speed was chosen as the main criterion. It was also noticed less aeration was favored in that less electron will be shunted to electron transfer chain. The fermentation in 500 l bioreactor produced 66.8 g 1,3-PD with the yield of 0.55 mol mol^?1 at agitation rate and aeration of 130 rpm and 0.14 vvm air flow. Using these empirically obtained control concepts we successfully scaled up in 500–50,000 l pilot-scale reactors. The final 1,3-PD concentrations in 50,000 l bioreactor amounted to 63.3 g l^?1 with the yield of 0.5 mol mol^?1.     

Degradation of synthetic reactive azo dyes and treatment of textile wastewater by a fungi consortium reactor

In this paper, two microbial cultures with high decolorization efficiencies of reactive dyes were obtained and were proved to be dominant with fungi consortium in which 21 fungal strains were isolated and 8 of them showed significant decolorization effect to reactive red M-3BE. A 4.5 l continuous biofilm reactor was established using the mixed cultures to investigate the decolorization performance and the system stability under the conditions of simulated and real textile wastewater as influents. The optimal nutrient feed to this bioreactor was 0.5 g l⁻¹ glucose and 0.1 g l⁻¹ (NH₄)₂SO₄ when 30 mg l⁻¹ reactive black 5 was used as initial dye concentrations. Dye mineralization rates of 50–75% and color removal efficiencies of 70–80% were obtained at 12 h hydraulic retention time (HRT) in this case. Higher glucose concentrations in the influents could significantly improve color removal, but was not helpful for dye mineralization. Besides reactive black 5, the bioreactor could effectively decolorize reactive red M-3BE, acid red 249 and real textile wastewater with efficiency of 65%, 94% and 89%, respectively. In addition, the microbial community on the biofilm was monitored in the whole running process. The results indicated fungi as a dominant population in the decolorization system with the ratio of fungi to bacteria 6.8:1 to 51.8:1 under all the tested influent conditions. Analysis of molecular biological detection indicated that yeasts of genus Candida occupied 70% in the fungal clone library based on 26S rRNA gene sequences.     

Degradation of the endocrine-disrupting dimethyl phthalate carboxylic ester by Sphingomonas yanoikuyae DOS01 isolated from the South China Sea and the biochemical pathway

Bacteria capable of using dimethyl phthalate (DMP) as the sole carbon and energy source were isolated from the sediments collected at a depth of 1340 m from the South China Sea. Sphingomonas yanoikuyae DOS01, identified based on 16S rRNA gene sequence, utilized DMP from an initial level of 180 mg l^?1 to non-detectable in 35 h at 30 °C, the optical density (OD₆₀₀) values increased over the time of incubation. Degradation intermediate monomethyl phthalate (MMP) accumulated up to 21.3 mg l^?1 and then disappeared in the culture medium. When MMP or another intermediate phthalate (PA) was used as the sole substrate, this strain was only capable of degrading MMP, but not PA. Total organic carbon (TOC) analysis of the culture medium suggested that both DMP and MMP were mineralized, but not PA. This strain from the deep-ocean sediment transforms DMP to MMP using a common biochemical pathway for DMP as reported before. Further esterase activity assays indicated that the enzyme induced by MMP has higher affinity than that by DMP for the substrate p-nitrophenyl acetate. Our results indicated that complete degradation of DMP by this marine microorganism may involve a new biochemical pathway.     

Immune responses,ROS generation and the haemocyte damage of scallop Chlamys farreri exposed to Aroclor 1254

The toxic effects of Aroclor 1254 (0.05, 0.5, 5 and 50 μg l^?1) on scallop (Chlamys farreri) immune system in vivo were studied. The results showed that Aroclor 1254 had significant toxic effect on the parameters tested in this paper (P < 0.05). The total number of haemocytes, the proportion of granulocytes, phagocytosis in all groups as well as the lysosomal membrane stability (LMS) in 5, 50 μg l^?1 and bacteriolytic activity 0.5, 5, 50 μg l^?1 treatments decreased significantly, while the proportion of hyalinocytes and the production of O₂^- in all treatments remarkably increased during the sampling time and tended to be stable gradually after 6–15 d. The bacteriolytic activity in 0.05 μg l^?1 treatments, LMS in 0.05, 0.5 μg l^?1 groups and the DNA damage (comet ratios and arbitrary values) in all treatments increased at the beginning of exposure and reached their peaks on day 1, day 1, day 6 and day 3, following that they all decreased gradually and became stable after 9–15 d. When the indices reached stability, except for DNA damage was higher than controls, the others were all significantly lower than those of controls (P < 0.05). Thus, Aroclor 1254 has evident toxic effects on scallop immune system, which supports the view that a relationship exists between pollution and immunomodulation in aquatic organisms. Also it supports the speculation that the PCBs pollution is one of the important reasons of the mass mortality of the C. farreri.     

Pilot-scale production of 1,3-propanediol using Klebsiella pneumoniae

The conversion of glycerol to 1,3-propanediol (PDO) using Klebsiella pneumoniae M5al under anaerobic condition was scaled up from scale 5 to 5000 l in series. A simple strategy for scale-up was to transfer the optimized conditions of a lab scale bioreactor to pilot-scale fermentation. Multistage inocula were developed and their fermentation abilities were assessed in a small-scale fermenter. The experimental results showed that inoculum development in the early steps of a scale-up process could influence the outcomes of a large scale fermentation. Through three-stage liquid inoculum development and a pulse addition of (NH₄)₂SO₄ and yeast extract at 30 h of fermentation, the best results in a 5000 l fermentation were achieved leading to 58.8 g l⁻¹ 1,3-propanediol with a yield of 0.53 mol mol⁻¹ glycerol and productivity of 0.92 g l⁻¹ h⁻¹. This is the first report on pilot-scale 1,3-propanediol production using K. pneumoniae.     

The effects of NH4+ and NO3− on growth,resource allocation and nitrogen uptake kinetics of Phragmites australis and Glyceria maxima

The effects of NH₄⁺ or NO₃⁻ on growth, resource allocation and nitrogen (N) uptake kinetics of two common helophytes Phragmites australis (Cav.) Trin. ex Steudel and Glyceria maxima (Hartm.) Holmb. were studied in semi steady-state hydroponic cultures. At a steady-state nitrogen availability of 34 μM the growth rate of Phragmites was not affected by the N form (mean RGR = 35.4 mg g⁻¹ d⁻¹), whereas the growth rate of Glyceria was 16% higher in NH₄⁺-N cultures than in NO₃⁻-N cultures (mean = 66.7 and 57.4 mg g⁻¹ d⁻¹ of NH₄⁺ and NO₃⁻ treated plants, respectively). Phragmites and Glyceria had higher S/R ratio in NH₄⁺ cultures than in NO₃⁻ cultures, 123.5 and 129.7%, respectively.Species differed in the nitrogen utilisation. In Glyceria, the relative tissue N content was higher than in Phragmites and was increased in NH₄⁺ treated plants by 16%. The tissue NH₄⁺ concentration (mean = 1.6 μmol g fresh wt⁻¹) was not affected by N treatment, whereas NO₃⁻ contents were higher in NO₃⁻ (mean = 1.5 μmol g fresh wt⁻¹) than in NH₄⁺ (mean = 0.4 μmol g fresh wt⁻¹) treated plants. In Phragmites, NH₄⁺ (mean = 1.6 μmol g fresh wt⁻¹) and NO₃⁻ (mean = 0.2 μmol g fresh wt⁻¹) contents were not affected by the N regime. Species did not differ in NH₄⁺ (mean = 56.5 μmol g⁻¹ root dry wt h⁻¹) and NO₃⁻ (mean = 34.5 μmol g⁻¹ root dry wt h⁻¹) maximum uptake rates (V_max), and V_max for NH₄⁺ uptake was not affected by N treatment. The uptake rate of NO₃⁻ was low in NH₄⁺ treated plants, and an induction phase for NO₃⁻ was observed in NH₄⁺ treated Phragmites but not in Glyceria. Phragmites had low K_m (mean = 4.5 μM) and high affinity (10.3 l g⁻¹ root dry wt h⁻¹) for both ions compared to Glyceria (K_m = 6.3 μM, affinity = 8.0 l g⁻¹ root dry wt h⁻¹). The results showed different plasticity of Phragmites and Glyceria toward N source. The positive response to NH₄⁺-N source may participates in the observed success of Glyceria at NH₄⁺ rich sites, although other factors have to be considered. Higher plasticity of Phragmites toward low nutrient availability may favour this species at oligotrophic sites.     

Morphology and bloom dynamics of Cochlodinium geminatum (Schütt) Schütt in the Pearl River Estuary,South China Sea

An unarmored dinoflagellate bloom of Cochlodinium geminatum (Schütt) Schütt has been identified in the Pearl River Estuary, South China Sea during the severe dry season, from late October to early November, 2009, when temperature and salinity ranged between 20.0–27.2 °C and 10.6–33.4, respectively. Light and scanning electron microscopy were used to identify the characteristics of C. geminatum and provided the clear morphological structure for this species. The organism was primarily found in chains of two cells or single cell, and no longer chains were observed. Cells were irregularly spherical or slightly dorso-ventrally, with size ranged between 28 and 36 μm and longer than wide. A large nucleus in the center with numerous golden chloroplasts was present, and the cingulum made 1.5 turns around the cell. The concentration of C. geminatum ranged from 10² to greater than 10⁷ cells l⁻¹ during the bloom period. Nutrient concentration ranges during the bloom were 1.29–81.00 μM NO₃, 0.14–12.14 μM NO₂, 0.21–6.29 μM NH₄, 0.23–6.26 μM PO₄ and 3.29–171.43 μM SiO₃, respectively. Total biomass expressed in terms of chlorophyll a ranged from 2.44 to 135.45 μg l⁻¹, with an average 19.9 μg l⁻¹ in surface water throughout the PRE. Two main clusters corresponding to the water sectors were defined with multivariate analysis (cluster and nMDS). Based on the composition and abundance of phytoplankton, spatial variations were observed at a significant level (ANOSIM, R = 0.44, P < 0.01). Although the pairwise correlation analysis detected no significant effect of any single environmental variable on the abundance of C. geminatum, the multivariate analysis (BIO-ENV) between biotic and abiotic variables resulted in the best variables combination with all measured factors involved (temperature, salinity, turbidity, NO₃, NO₂, NH₄, PO₄ and SiO₃) which showed a combined effect during the bloom of C. geminatum in the Pearl River Estuary (ρ_w = 0.477).