Kinetic characteristics and modelling of growth and substrate removal by <Emphasis Type="Italic">Alcaligenes faecalis</Emphasis> strain NR

Alcaligenes faecalis strain NR has the capability of simultaneous ammonium and organic carbon removal under sole aerobic conditions. The growth and substrate removal characteristics of A. faecalis strain NR were studied and appropriate kinetic models were developed. The maximum substrate removal rate of NH₄ ⁺-N and TOC were determined as 2.27 mg NH₄ ⁺-N/L/h and 30.00 mg TOC/L/h, respectively with initial NH₄ ⁺-N = 80 mg/L and TOC = 800 mg/L. Single-substrate models and double-substrate models based on Monod, Contois, Moser and Teissier were employed to describe the bioprocess kinetic coefficients. As a result, two double-substrate models, Teissier-Contois and Contois-Contois, were considered to be appropriate to model growth kinetics with both NH₄ ⁺-N and TOC as limiting substrates. The kinetic constants of maximum growth rate (μ _max) and half-saturation constant (K _S and B _S) were obtained by solving multiple equations with regression. This work can be used to further understand and predict the performance of heterotrophic nitrifiers, and thus provides specific guidance of these functional strains in practical wastewater treatment process.     

Effect of influent substrate ratio on anammox granular sludge: performance and kinetics

Effect of influent substrate ratio on anammox process was studied in sequencing batch reactor. Operating temperature was fixed at 35 ± 1 °C. Influent pH and hydraulic retention time were 7.5 and 6 h, respectively. When influent NO₂ ^?-N/NH₄ ⁺-N was no more than 2.0, total nitrogen removal rate (TNRR) increased whereas NH₄ ⁺-N removal rate stabilized at 0.32 kg/(m³ d). ΔNO₂ ^?-N/ΔNH₄ ⁺-N increased with enhancing NO₂ ^?-N/NH₄ ⁺-N. When NO₂ ^?-N/NH₄ ⁺-N was 4.5, ΔNO₂ ^?-N/ΔNH₄ ⁺-N was 1.98, which was much higher than theoretical value (1.32). The IC₅₀ of NO₂ ^?-N was 289 mg/L and anammox activity was inhibited at high NO₂ ^?-N/NH₄ ⁺-N ratio. With regard to influent NH₄ ⁺-N/NO₂ ^?-N, the maximum NH₄ ⁺-N removal rate was 0.36 kg/(m³ d), which occurred at the ratio of 4.0. Anammox activity was inhibited when influent NH₄ ⁺-N/NO₂ ^?-N was higher than 5.0. With influent NO₃ ^?-N/NH₄ ⁺-N of 2.5–6.5, NH₄ ⁺-N removal rate and NRR were stabilized at 0.33 and 0.40 kg/(m³ d), respectively. When the ratio was higher than 6.5, nitrogen removal would be worsened. The inhibitory threshold concentration of NO₂ ^?-N was lower than NH₄ ⁺-N and NO₃ ^?-N. Anammox bacteria were more sensitive to NO₂ ^?-N than NH₄ ⁺-N and NO₃ ^?-N. TNRR would be enhanced with increasing nitrogen loading rate, but sludge floatation occurred at high nitrogen loading shock. The Han-Levenspiel could be applied to simulate nitrogen removal resulting from NO₂ ^?-N inhibition.     

Inorganic nitrogen uptake kinetics of sugarcane (Saccharum spp.) varieties under in vitro conditions with varying N supply

An in vitro system was established for the characterisation of inorganic nitrogen uptake by sugarcane plantlets of variety NCo376. After multiplication and rooting, plantlets (0.27–0.3 g fresh mass) were placed on N-free medium for 4 days, and then supplied with 2–20 mM N as NO₃ ^?-N only, NH₄ ⁺-N only or NO₃ ^?-N + NH₄ ⁺-N (as 1:1). With few exceptions, on all the tested N media, the in vitro plants always had a higher V_max for NH₄ ⁺-N (28.69–66.51 μmol g^?1 h^?1) than for NO₃ ^?-N uptake (10.24–30.19 μmol g^?1 h^?1) and the K_m indicated a higher affinity for NO₃ ^?-N (0.02–7.38 mM) than for NH₄ ⁺-N (0.06–9.15 mM). When N was applied as 4 and 20 mM to varieties N12, N19 and N36, the interaction between variety, N form and concentration resulted in differences in the V_max and K_m. The high N-use efficient varieties (N12 and N19), as determined in previous pot and field trials, behaved similarly under all tested conditions and displayed a lower V_max and K_m than the low N-use efficient ones (NCo376 and N36). Based on this finding, it was suggested that the N-use efficient designation (from pot and field trials) may not be ascribed solely to N uptake. Assessment of the relative preference index (RPI) for NO₃ ^?-N and NH₄ ⁺-N uptake revealed that, at present, the RPI has no application in sugarcane due to its preferential uptake of NH₄ ⁺-N.     

Simultaneous nitrification and denitrification with different mixed nitrogen loads by a hypothermia aerobic bacterium

Microorganism with simultaneous nitrification and denitrification ability plays a significant role in nitrogen removal process, especially in the eutrophic waters with excessive nitrogen loads. The nitrogen removal capacity of microorganism may suffer from low temperature or nitrite nitrogen source. In this study, a hypothermia aerobic nitrite-denitrifying bacterium, Pseudomonas tolaasii strain Y-11, was selected to determine the simultaneous nitrification and denitrification ability with mixed nitrogen source at 15 °C. The sole nitrogen removal efficiencies of strain Y-11 in simulated wastewater were obtained. After 24 h of incubation at 15 °C, the ammonium nitrogen fell below the detection limit from an initial value of 10.99 mg/L. Approximately 88.0 ± 0.33% of nitrate nitrogen was removed with the initial concentration of 11.78 mg/L and the nitrite nitrogen was not detected with the initial concentration of 10.75 mg/L after 48 h of incubation at 15 °C. Additionally, the simultaneous nitrification and denitrification nitrogen removal ability of P. tolaasii strain Y-11 was evaluated using low concentration of mixed NH₄⁺-N and NO₃^?–N/NO₂^?–N (about 5 mg/L-N each) and high concentration of mixed NH₄⁺–N and NO₃^?–N/NO₂^?–N (about 100 mg/L-N each). There was no nitrite nitrogen accumulation at the time of evaluation. The results demonstrated that P. tolaasii strain Y-11 had higher simultaneous nitrification and denitrification capacity with low concentration of mixed inorganic nitrogen sources and may be applied in low temperature wastewater treatment.     

Seasonal and geomorphic controls on N and P removal in riparian zones of the US Midwest

Riparian zones are an important strategy to mitigate N and P export to streams. However, their efficiency with respect to nitrate (NO₃ ^?), ammonium (NH₄ ⁺), or soluble reactive phosphorus (SRP) in groundwater remains uncertain in the US Midwest. This study investigates water table fluctuations and NO₃ ^?, NH₄ ⁺, and SRP concentration dynamics in two riparian zone types (outwash vs. glacial till) common in the upper US Midwest. During low water table periods, NO₃ ^? removal was 93 % at WR (outwash site), and 75 % at LWD (glacial till site); but during high water table periods, NO₃ ^? removal efficiencies dropped to 50 % at WR, and 14 % at LWD. Median seasonal mass fluxes of NO₃ ^? removed at WR (9.4–21.7 mg N day^?1 m^?1 of stream length) and LWD (0.4–1.9 mg N day^?1 m^?1) were small compared to other riparian zones in glaciated landscapes. The WR site was a small SRP sink (0.114 and 0.118 mg day^?1 m^?1 during the dry period and wet period, respectively), while LWD acted as a small SRP source to the stream (0.004 mg day^?1 m^?1 during the dry period; 0.075 mg day^?1 m^?1 during the wet period). Both LWD and WR acted as sources of NH₄ ⁺ to the stream with mass fluxes ranging from 0.17 to 7.75 mg N day^?1 m^?1. Although riparian zones in the US Midwest provide many ecosystem services, results suggest they are unlikely to efficiently mitigate N and P pollution in subsurface flow.     

The Significance of Myriophyllum elatinoides for Swine Wastewater Treatment: Abundance and Community Structure of Ammonia-Oxidizing Microorganisms in Sediments

Myriophyllum elatinoides was reported to effectively treat wastewater by removing nitrogen (N) and phosphorus (P). However, little is known about the abundance and community structure of ammonia-oxidizing microorganisms associated with M. elatinoides purification systems. The objective of this research was to characterize the abundance and community structure of ammonia-oxidizing microorganisms in swine wastewater and determine the main nitrogen removal pathways. In this study, five different waters were treated by M. elatinoides in microcosms for one month. The five waters included tap water (Control), swine wastewater (SW), 50% diluted swine wastewater (50% SW), and two synthetic wastewaters: 200 mg NH₄ ⁺-N L⁻¹ (200 NH₄ ⁺-N) and 400 mg NH₄ ⁺-N L⁻¹ (400 NH₄ ⁺-N). The most dramatic changes were in NH₄ ⁺-N and total N (TN) concentrations, with average removal rates of 84% and 90%, respectively, in the treatments containing swine wastewater. On days 7, 14, and 28, the dissolved oxygen (DO) increased by 81.8%, 210.4% and 136.5%, respectively, compared with on day 0, in the swine wastewater. The results also showed that the bacterial amoA (AOB) copy numbers in the sediments of the treatments were significantly higher than those of archaeal amoA (AOA) copy numbers (p = 0.015). In addition, the high DO concentrations in swine wastewater responded well to the high abundance of AOB. The AOA and AOB community distributions were positively related with NO₃ ^-N and were negatively related with DO in swine wastewater treatments. In summary, our experimental results suggested that the M. elatinoides purification system could improve the activity of ammonia-oxidizing microorganisms and consequently might contribute to the significant N removal from the swine wastewater.     

The effect of nutrient concentrations,nutrient ratios and temperature on photosynthesis and nutrient uptake by Ulva prolifera: implications for the explosion in green tides

The green-tide macroalga, Ulva prolifera, was tested in the laboratory to determine its nutrient uptake and photosynthesis under different conditions. In the nutrient concentration experiments U. prolifera showed a saturated uptake for nitrate but an escalating uptake in the tested range for phosphorus. Both N/P and NO₃ ^?/NH₄ ⁺ ratios influenced nutrient uptake significantly (p?<?0.05) while the PSII quantum yield [Y(II)] (p?>?0.05) remained unaffected. The maximum N uptake rate (33.9?±?0.8 μmol g^?1 DW h^?1) and P uptake rate (11.1?±?4.7) was detected at N/P ratios of 7.5 and 2.2, respectively. U. prolifera preferred NH₄ ⁺-N to NO₃ ^?-N when the NO₃ ^?-N/NH₄ ⁺-N ratio was less than 2.2 (p?<?0.05). But between ratios of 2.2 and 12.9, the uptake of NO₃ ^?-N surpassed that of NH₄ ⁺-N. In the temperature experiments, the highest N uptake rate and [Y(II)] were observed at 20 °C, while the lowest rates were detected at 5 °C. P uptake rates were correlated with increasing temperature.     

Effects of olive mill wastewater on soil carbon and nitrogen cycling

This study investigated the cycling of C and N following application of olive mill wastewater (OMW) at various rates (0, 42, 84, and 168 m³/ha). OMW stimulated respiration rate throughout the study period, but an increase in soil organic matter was observed only at the highest rate. Soil phenol content decreased rapidly within 2 weeks following application but neither phenol oxidase and peroxidase activity nor laccase gene copies could explain this response. Soil NH₄ ⁺-N content increased in response to OMW application rate, while an opposite trend observed for NO₃ ^?-N, which attributed to immobilization. This decrease was in accordance with amoA gene copies of archaeal and bacterial ammonia oxidizers in the first days following OMW application. Afterwards, although amoA gene copies and potential nitrification rates recovered to values similar to or higher than those in the non-treated soils, NO₃ ^?-N content did not change among the treatments. A corresponding increase in denitrifying gene copies (nirK, nirS, nosZ) during that period indicates that denitrification, stimulated by OMW application rate, was responsible for this effect; a hypothesis consistent with the decrease in total Kjeldahl nitrogen content late in the season. The findings suggest that land application of OMW is a promising practice for OMW management, even at rates approaching the soil water holding capacity.     

Pyridine degradation characteristics of a newly isolated bacterial strain and its application with a novel reactor for the further treatment in pyridine wastewater

A pyridine-degrading strain Gemmobacter sp. ZP-12, isolated from an activated sludge, was able to use pyridine as the sole carbon and nitrogen source for the growth. The strain could effectively degrade pyridine and remove TOC over a wide range of initial pyridine concentrations. The pyridine degradation rate for 100, 500, 1000, 1500 and 2000 mg/L was 2.90 ± 0.17; 13.72 ± 0.21, 20.40 ± 0.24, 31.09 ± 0.26, 27.63 ± 0.17 mg/L/h, respectively. During the pyridine degraded, a large amount of NH₄⁺-N was released and accumulated. The accumulation of NH₄⁺-N increased with the increase of pyridine concentration. For further removing the NH₄⁺-N producing in pyridine degradation, an aerobic-moving bed biofilm reactor coupled with intermittent-aeration membrane biological reactor (a-MBBR-IMBR) was constructed, in which the strain and the aerobic / anoxic mixed sludge combined to remove the pollutants in the wastewater containing 500 mg/L pyridine. After 96 h of operation, the final TOC removal efficiency was 96.5 ± 1.05 %. The average residual concentration of NO₃⁻-N and NH₄⁺-N was respectively 9.09 ± 4.13 mg/L and 7.85 ± 3.88 mg/L. The study provides a viable option for treating pyridine wastewater.     

Withanolide A production from Withania somnifera hairy root cultures with improved growth by altering the concentrations of macro elements and nitrogen source in the medium

Withania somnifera is an important medicinal plant that contains withanolides as bioactive compounds. We have investigated the effects of macroelements and nitrogen source in hairy roots of W. somnifera with the aim of optimizing the production of biomass and withanolide A content. The effects of the macroelements NH₄NO₃, KNO₃, CaCl₂, MgSO₄ and KH₂PO₄ at concentrations of 0, 0.5, 1.0, 1.5 and 2.0× strengths and of nitrogen source [NH₄ ⁺/NO₃ ^? (0.00/18.80, 7.19/18.80, 14.38/18.80, 21.57/18.80, 28.75/18.80, 14.38/0.00, 14.38/9.40, 14.38/18.80, 14.38/28.20 and 14.38/37.60 mM)] in Murashige and Skoog medium were evaluated for biomass and withanolide A production. The highest accumulation of biomass (139.42 g l^?1 FW and 13.11 g l^?1 DW) was recorded in the medium with 2.0× concentration of KH₂PO₄, and the highest production of withanolide A was recorded with 2.0× KNO₃ (15.27 mg g^?1 DW). The NH₄ ⁺/NO₃ ^? ratio also influenced root growth and withanolide A production, with both parameters being larger when the NO₃ ^? concentration was higher than that of NH₄ ⁺. Maximum biomass growth (148.17 g l^?1 FW and 14.79 g l^?1 DW) was achieved at NH₄ ⁺/NO₃ ^? ratio of 14.38/37.60 mM, while withanolide A production was greatest (14.68 mg g^?1 DW) when the NH₄ ⁺/NO₃ ^? ratio was 0.00/18.80 mM. The results are useful for the large scale cultivation of Withania hairy root culture for the production of withanolide A.     

Heterotrophic nitrification and aerobic denitrification by a novel Halomonas campisalis

A novel halophilic strain that could carry out heterotrophic nitrification and aerobic denitrification was isolated and named as Halomonas campisalis ha3. It removed inorganic nitrogen compounds (e.g. NO₃ ^?, NO₂ ^? and NH₄ ⁺) simultaneously, and grew well in the medium containing up to 20 % (w/v) NaCl. PCR revealed four genes in the genome of ha3 related to aerobic denitrification: napA, nirS, norB and nosZ. The optimal conditions for aerobic denitrification were pH 9.0, at 37 °C, with 4 % (w/v) NaCl and sodium succinate as carbon source. The nitrogen removal rate was 87.5 mg NO₃ ^?–N l^?1 h^?1. Therefore, this strain is a potential aerobic denitrifier for the treatment of saline wastewater.     

Biodegradation of 4-nitrotoluene with biosurfactant production by Rhodococcus pyridinivorans NT2: metabolic pathway, cell surface properties and toxicological characterization

A novel 4-nitrotoluene-degrading bacterial strain was isolated from pesticides contaminated effluent-sediment and identified as Rhodococcus pyridinivorans NT2 based on morphological and biochemical properties and 16S rDNA sequencing. The strain NT2 degraded 4-NT (400 mg l^?1) with rapid growth at the end of 120 h, reduced surface tension of the media from 71 to 29 mN m^?1 and produced glycolipidic biosurfactants (45 mg l^?1). The biosurfactant was purified and characterized as trehalose lipids. The biosurfactant was stable in high salinity (10 % w/v NaCl), elevated temperatures (120 °C for 15 min) and a wide pH range (2.0–10.0). The noticeable changes during biodegradation were decreased hydrophobicity; an increase in degree of fatty acid saturation, saturated/unsaturated ratio and cyclopropane fatty acid. Biodegradation of 4-NT was accompanied by the accumulation of ammonium (NH₄ ⁺) and negligible amount of nitrite ion (NO₂ ^?). Product stoichiometry showed a carbon (C) and nitrogen (N) mass balance of 37 and 35 %, respectively. Biodegradation of 4-NT proceeded by oxidation at the methyl group to form 4-nitrobenzoate, followed by reduction and hydrolytic deamination yielding protocatechuate, which was metabolized through β-ketoadipate pathway. In vitro and in vivo acute toxicity assays in adult rat (Rattus norvegicus) showed sequential detoxification and the order of toxicity was 4-NT >4-nitrobenzyl alcohol >4-nitrobenzaldehyde >4-nitrobenzoate >> protocatechuate. Taken together, the strain NT2 could be used as a potential bioaugmentation candidate for the bioremediation of contaminated sites.     

Subcellular Localization and Kinetic Characterization of a Gill (Na+, K+)-ATPase from the Giant Freshwater Prawn Macrobrachium rosenbergii

The stimulation by Mg²⁺, Na⁺, K⁺, NH₄ ⁺, and ATP of (Na⁺, K⁺)-ATPase activity in a gill microsomal fraction from the freshwater prawn Macrobrachium rosenbergii was examined. Immunofluorescence labeling revealed that the (Na⁺, K⁺)-ATPase α-subunit is distributed predominantly within the intralamellar septum, while Western blotting revealed a single α-subunit isoform of about 108 kDa M _r. Under saturating Mg²⁺, Na⁺, and K⁺ concentrations, the enzyme hydrolyzed ATP, obeying cooperative kinetics with V _M = 115.0 ± 2.3 U mg^?1, K _0.5 = 0.10 ± 0.01 mmol L^?1. Stimulation by Na⁺ (V _M = 110.0 ± 3.3 U mg^?1, K _0.5 = 1.30 ± 0.03 mmol L^?1), Mg²⁺ (V _M = 115.0 ± 4.6 U mg^?1, K _0.5 = 0.96 ± 0.03 mmol L^?1), NH₄ ⁺ (V _M = 141.0 ± 5.6 U mg^?1, K _0.5 = 1.90 ± 0.04 mmol L^?1), and K⁺ (V _M = 120.0 ± 2.4 U mg^?1, K _M = 2.74 ± 0.08 mmol L^?1) followed single saturation curves and, except for K⁺, exhibited site–site interaction kinetics. Ouabain inhibited ATPase activity by around 73 % with K _I = 12.4 ± 1.3 mol L^?1. Complementary inhibition studies suggest the presence of F₀F₁–, Na⁺-, or K⁺-ATPases, but not V(H⁺)- or Ca²⁺-ATPases, in the gill microsomal preparation. K⁺ and NH₄ ⁺ synergistically stimulated enzyme activity (≈25 %), suggesting that these ions bind to different sites on the molecule. We propose a mechanism for the stimulation by both NH₄ ⁺, and K⁺ of the gill enzyme.     

Kinetic Modeling for Simultaneous Organic Carbon Oxidation,Nitrification, and Denitrification of Abattoir Wastewater in Sequencing Batch Reactor

A laboratory-scale study was conducted in a 20.0-L sequencing batch reactor (SBR) to explore the feasibility of simultaneous removal of organic carbon and nitrogen from abattoir wastewater. The reactor was operated under three different combinations of aerobic-anoxic sequence, viz., (4+4), (5+3), and (5+4) h of total react period, with influent soluble chemical oxygen demand (SCOD) and ammonia nitrogen (NH₄⁺-N) level of 2200 ± 50 and 125 ± 5 mg L^?1, respectively. In (5+4) h cycle, a maximum 90.27% of ammonia reduction corresponding to initial NH₄⁺-N value of 122.25 mg L^?1 and 91.36% of organic carbon removal corresponding to initial SCOD value of 2215.25 mg L^?1 have been achieved, respectively. The biokinetic parameters such as yield coefficient (Y), endogenous decay constant (k_d), and half-velocity constant (K_s) were also determined to improve the design and operation of package effluent treatment plants comprising SBR units. The specific denitrification rate (q_DN) during anoxic condition was estimated as 6.135 mg N/g mixed liquor volatile suspended solid (MLVSS)·h on 4-h average contact period. The value of Y, k_d and K_s for carbon oxidation and nitrification were found to be in the range of 0.6225–0.6952 mg VSS/mg SCOD, 0.0481–0.0588 day^?1, and 306.56–320.51 mg L^?1, and 0.2461–0.2541 mg VSS/mg NH₄⁺-N, 0.0324–0.0565 day^?1, and 38.28–50.08 mg L^?1, respectively, for different combinations of react periods.     

The role of gross and net N transformation processes and NH4 + and NO3 − immobilization in controlling the mineral N pool of a temperate mixed deciduous forest soil

In many forests of Europe and north-eastern North America elevated N deposition has opened the forest N cycle, resulting in NO₃ ^? leaching. On the other hand, despite this elevated N deposition, the dominant fate of NO₃ ^? and NH₄ ⁺ in some of these forests is biotic or abiotic immobilization in the soil organic matter pool, preventing N losses. The environmental properties controlling mineral N immobilization and the variation and extent of mineral N immobilization in forest soils are not yet fully understood. In this study we investigated a temperate mixed deciduous forest, which is subjected to an average N deposition of 36.5 kg N ha^?1 yr^?1, but at the same time shows low NO₃ ^? concentrations in the groundwater. The aim of this study was to investigate whether the turnover rate of the mineral N pool could explain these low N leaching losses. A laboratory ¹⁵N pool dilution experiment was conducted to study gross and net N mineralization and nitrification and mineral N immobilization in the organic and uppermost (0–10 cm) mineral layer of the forest soil. Two locations, one at the forest edge (GE) and another one 145 m inside the forest (GF1), were selected. In the organic layers of GE and GF1, the gross N mineralization averaged 10.9 and 11.1 mg N kg^?1 d^?1, the net N mineralization averaged 6.1 and 6.8 mg N kg^?1 d^?1 and NH₄ ⁺ immobilization rates averaged 3.8 and 3.6 mg N kg^?1 d^?1. In the organic layer of GE and GF1, the average gross nitrification was 3.8 and 4.6 mg N kg^?1 d^?1, the average net nitrification was ?25.2 and ?31.3 mg N kg^?1 d^?1 and the NO₃ ^? immobilization rates averaged 29.0 and 35.9 mg N kg^?1 d^?1. For the mineral (0–10 cm) layer the same trend could be observed, but the N transformation rates were much lower for the NH₄ ⁺ pool and not significantly different from zero for the NO₃ ^? pool. Except for the turnover of the NH₄ ⁺ pool in the mineral layer, no significant differences were observed between location GE and GF1. The ratio of NH₄ ⁺ immobilization to gross N mineralization, gross N mineralization to gross nitrification, and NO₃ ^? immobilisation to gross nitrification led to the following observations. The NH₄ ⁺ pool of the forest soil was controlled by N mineralization and NO₃ ^? immobilization was importantly controlling the forest NO₃ ^? pool. Therefore it was concluded that this process is most probably responsible for the limited NO₃ ^? leaching from the forest ecosystem, despite the chronically high N deposition rates.     

Biodegradation of para-nitrophenol by Citricoccus nitrophenolicus strain PNP1T at high pH

A gram-positive bacterium Citricoccus nitrophenolicus (strain PNP1^T, DSM 23311^T, CCUG 59571^T) isolated from a waste water treatment plant was capable of effectively degrading p-nitrophenol (pNP) as a source of carbon, nitrogen and energy for growth. Degradation of pNP required oxygen and resulted in the stoichiometric release of nitrite. Strain PNP1^T also degraded 4-chlorophenol, phenol and salicylate. pNP was degraded at pH values between 6.8 and 10.0 and at temperatures between 15–32 °C. pNP at concentrations up to 150 mg L^?1 were degraded during growth in media at pH ≤ 10, whereas 200 mg L^?1 was completely inhibitory to growth. When incubated in an NH₄Cl-free medium (pH 10) containing both pNP and acetate, pNP is degraded with concomitant release of nitrite which was subsequently assimilated during acetate degradation. Intact cells of strain PNP1^T suspended in NaHCO₃/Na₂CO₃ buffer were able to continuously degrade 200 mg L^?1 pNP over a 40 day period at pH 10.     

Plant regeneration of the arsenic hyperaccumulator <Emphasis Type="Italic">Pteris vittata</Emphasis> L<Emphasis Type="Italic">.</Emphasis> from spores and identification of its tolerance and accumulation of arsenic and copper

An in vitro plant regeneration system was established from the spores of Pteris vittata and identification of its tolerance, and accumulation of gametophytes and callous, to arsenic (As) and copper (Cu) was investigated. The highest frequency (100%) of callus formation was achieved from gametophyte explants treated with 0.5 mg l^?1 6-benzylaminopurine (6-BA) + 0.5 mg l^?1 gibberellin acid (GA). Furthermore, sporophytes were differentiated from the callus tissue derived from gametophyte explants on MS medium supplemented with 0.5 mg l^?1 6-BA, 0.5–1.0 mg l^?1 GA and additional 300 mg l^?1 lactalbumin hydrolysate (LH) for 4 weeks. The optimum combination of ½ MS + 1.0 mg l^?1 GA + 0.5 mg l^?1 6-BA + 300 mg l^?1 LH promoted sporophyte formation on 75 ± 10% of the callus. Every callus derived from gametophyte explants could achieve 3–4 sporophytes. The in vitro growth of gametophyte and callus was accelerated in the medium containing Na₃AsO₄ lower than 0.5 mM, but this growth was inhibited with 2 mM Na₃AsO₄. And with the increase of Na₃AsO₄ in the culture medium from 0 to 2 mM, the As accumulation in gametophytes and callus increased and achieved a level of 763.3 and 315.4 mg kg^?1, respectively. Gametophytes and calluses transplanted to culture medium, supplemented with different concentrations of CuSO₄, are similar to those in Na₃AsO₄, and the Cu accumulation in gametophytes could achieve 7,940 mg kg^?1 when gametophytes were subcultured in medium containing 3 mM CuSO₄. These results suggested that the high efficiency propagation system could be a useful and rapid means to identify other heavy metal tolerance and accumulation. Further, the regeneration ability of callus made it possible for genetic transformation of this fern.     

Ammonium,nitrate, and urea play different roles for lipid accumulation in the nervonic acid—producing microalgae <Emphasis Type="Italic">Mychonastes afer</Emphasis> HSO-3-1

Producing valuable coproducts from oleaginous microalgae is an option to reduce the total cost of biofuel production. Here, the influence of nitrogen sources on biomass yield and lipid accumulation of a newly identified oleaginous green microalgal strain, Mychonastes afer HSO-3-1, was evaluated. Carbon assimilation and the following lipid biosynthesis of M. afer were inhibited to some extent under weak acidic conditions (6 < pH < 7) and any of the tested nitrogen source. The highest lipid productivity of 50.7 mg L^?1 day^?1 was achieved with a 17.6 mM nitrogen supplement in the form of urea. The cell polar lipid content was significantly higher than triacylglycerol (TAG), and saturated palmitic acid (C16:0) occupied a dominant position in the fatty acid profiles while culturing M. afer in acidic medium with NH₄ ⁺ as the nitrogen source. Under neutral conditions, the lipid productivities of M. afer cultivated in media containing 17.6 mM of NaNO₃, NH₄Cl, and NH₄NO₃ were 76.2, 77.5, and 79.0 mg L^?1 day^?1, respectively. The greatest TAG content (58.56%) of total lipids was obtained when NaNO₃ was used as the nitrogen source. There was no significant difference in the fatty acid composition of M. afer cells when they were cultivated in neutral media supplemented with NaNO₃, urea, NH₄Cl, and NH₄NO₃. Therefore, NH₄ ⁺ was not a suitable nitrogen source for M. afer cultivation due to the additional labor, working procedures, and alkali required to adjust the medium pH. Considering that using urea as nitrogen source could reduce the cost of nutrient salts substantially and urea can be taken up and utilized by most microalgae, it is a preferred nitrogen source. The major properties of biodiesel derived from M. afer HSO-3-1 met biodiesel quality, and nervonic acid concentrations remained at approximately 3.0% of total fatty acids.     

Dynamic variations of microbial community structure in Myriophyllum aquaticum constructed wetlands in response to different NH4+-N concentrations

Constructed wetlands (CWs) have received increasing attentions for their N removal performances, especially regarding NH₄⁺-N. Different influent NH₄⁺-N concentration may influence N removal efficiency in practice, while the effects of different NH₄⁺-N concentrations on microorganisms removing N in CWs are poorly understood. In this study, surface flow CWs planted with Myriophyllum (M). aquaticum were established to investigate the influences of different NH₄⁺-N concentrations on the composition, structure, and interactions of microbial community. Our findings suggested 105 mg/L NH₄⁺-N CWs achieved highest N removal rate, removing 89.30 % NH₄⁺-N and 92.34 % TN from the influent. The results of real-time quantitative polymerase chain reactions (qPCR) indicated abundances of nitrifying genes (nxrA) and denitrifying genes (narG, nirS, nirK, and nosZ) were increased by increasing NH₄⁺-N concentrations, and the strongest effects were observed in narG (8-fold) and nosZ genes (11-fold). Different NH₄⁺-N concentrations was proved to alter composition and structure of microbial communities via high-throughput sequencing, e.g. denitrifiers including Brevendomonas.sp, Dokdonella.sp and Rhodococcus.sp were enriched obviously with increasing NH₄⁺-N concentrations. In addition, network showed interactions among microbial populations and positive interactions were dramatically shifted and enhanced by increasing NH₄⁺-N concentrations.     

Influence of Agapanthus africanus on nitrification in a vertical subsurface flow constructed wetland

The aim of this study is to evaluate the influence of Agapanthus africanus (A. africanus) on nitrification in a vertical subsurface flow constructed wetlands (VSSFs) system. Two lab-scale VSSFs were operated: a) one was planted with A. africanus (vertical flow planted, VFP), and b) the other was unplanted (vertical flow control, VFC). The operation strategy was divided into three phases and consisted of increasing the ammoniacal nitrogen loading rate (ALR) (Phase I: 1.4; Phase II: 2.4; Phase III: 4.4 g NH₄⁺-N·m^?2·d^?1). Nitrification was evaluated in the system at two different depths in the VSSFs (30.5 cm and 60.3 cm, from the top of the system).

The removal efficiencies of COD, BOD₅, TP, and PO₄^?3-P were above 40% in the VFP and VFC during all operation. The mean removal efficiencies of NH₄⁺-N were above 70%. Nitrification was the principal NH₄⁺-N removal mechanism in both systems and transformed more than 50% of the NH₄⁺-N to NO₃^?-N. In terms of the effect of A. africanus on NH₄⁺-N removal during the three operational phases, nonsignificant differences between the two VSSFs were noted (p > 0.05). Thus, A. africanus did not influence nitrification. Finally, the analysis at different depths showed that nitrification occurred in the upper 30.5 cm.