Isolation of Arsenic-Resistant Bacteria from Bengal Delta Sediments and their Efficacy in Arsenic Removal from Soil in Association with Pteris vittata

The potential of arsenic-resistant bacteria in association with Pteris vittata to reduce the level of arsenic from soil was studied. The physicochemical characteristics of contaminated paddy soil were analyzed, and 3 bacterial isolates amongst 11 were screened and were selected for further study. These three isolates were characterized by 16S rDNA sequencing and identified as Bacillus altitudinis Strain SS8 (KJ432582), Bacillus megaterium Strain SS9 (KJ432583) and Lysinibacillus sp. Strain SS11 (KJ432584). Of these, Lysinibacillus sp. Strain SS11 displayed arsenic tolerance of 3256 mg L^?1 for arsenate and 1136 mg L^?1 for arsenite. Additionally, it showed bioaccumulation capacity of 23.43 mg L^?1 for arsenate and 5.65 mg L^?1 for arsenite. It also showed resistance to other heavy metals, especially towards iron, copper and chromium. It was also observed that Pteris vittata was able to take up more arsenic and iron from soil in the presence of these bacterial strains than in their absence, leading to contaminant-free soil. Thus, this system appears to be an effective bioremediating process to remove arsenic from contaminated soil.     

Characterization of As(III) oxidizing <Emphasis Type="Italic">Achromobacter</Emphasis> sp. strain N2: effects on arsenic toxicity and translocation in rice

Achromobacter sp. strain N2 was isolated from a pyrite-cinder-contaminated soil and presented plant growth promoting traits (ACC deaminase activity, production of indole-3-acetic and jasmonic acids, siderophores secretion, and phosphate solubilization) and arsenic transformation abilities. Achromobacter sp. strain N2 was resistant to different metals and metalloids, including arsenate (100 mM) and arsenite (5 mM). The strain was resistant to ionic stressors (i.e., arsenate and NaCl), whereas bacterial growth was impaired by osmotic stress. Strain N2 was able to oxidize 1.0 mmol L^?1 of arsenite to arsenate in 72 h. This evidence was supported by the retrieval of an arsenite oxidase AioA gene highly homologous to arsenite oxidases of Achromobacter and Alcaligenes species. Rice seeds of Oryza sativa (var. Loto) were bio-primed with ACCD-induced and non-induced cells in order to evaluate the effect of inoculation on rice seedlings growth and arsenic uptake. The bacterization with ACCD-induced cells significantly improved seed germination and seedling heights if compared with the seeds inoculated with non-induced cells and non-primed seeds. Enhanced arsenic uptake was evidenced in the presence of ACCD-induced cells, suggesting a role of ACCD activity on the mitigation of the toxicity of arsenic accumulated by the plant. This kind of responses should be taken into account when proposing PGP strains for improving plant growth in arsenic-rich soils.     

Rhizosphere colonization and arsenic translocation in sunflower (Helianthus annuus L.) by arsenate reducing Alcaligenes sp. strain Dhal-L

In the present study, six arsenic-resistant strains previously isolated were tested for their plant growth promoting characteristics and heavy metal resistance, in order to choose one model strain as an inoculum for sunflower plants in pot experiments. The aim was to investigate the effect of arsenic-resistant strain on sunflower growth and on arsenic uptake from arsenic contaminated soil. Based on plant growth promoting characteristics and heavy metal resistance, Alcaligenes sp. strain Dhal-L was chosen as an inoculum. Beside the ability to reduce arsenate to arsenite via an Ars operon, the strain exhibited 1-amino-cyclopropane-1-carboxylic acid deaminase activity and it was also able to produce siderophore and indole acetic acid. Pot experiments were conducted with an agricultural soil contaminated with arsenic (214 mg kg^?1). A real time PCR method was set up based on the quantification of ACR3(2) type of arsenite efflux pump carried by Alcaligenes sp. strain Dhal-L, in order to monitor presence and colonisation of the strain in the bulk and rhizospheric soil. As a result of strain inoculation, arsenic uptake by plants was increased by 53 %, whereas ACR3(2) gene copy number in rhizospheric soil was 100 times higher in inoculated than in control pots, indicating the colonisation of strain. The results indicated that the presence of arsenate reducing strains in the rhizosphere of sunflower influences arsenic mobilization and promotes arsenic uptake by plant.     

Lipid productivity and fatty acid composition in Chlorella and Scenepdesmus strains grown in nitrogen-stressed conditions

Thirty Chlorella and 30 Scenedesmus strains grown in nitrogen-stressed conditions (70 mg L^?1 N) were analyzed for biomass accumulation, lipid productivity, protein, and fatty acid (FA) composition. Scenedesmus strains produced more biomass (4.02?±?0.73 g L^?1) after 14 days in culture compared to Chlorella strains (2.57?±?0.12 g L^?1). Protein content decreased and lipid content increased from days 8 to 14 with an increase in triacylglycerol (TAG) accumulation in most strains. By day 14, Scenedesmus strains generally had higher lipid productivity (53.5?±?3.7 mg lipid L^?1 day^?1) than Chlorella strains (35.1?±?2.8 mg lipid L^?1 day^?1) with the lipids consisting mainly of C16–18 TAGs. Scenedesmus strains generally had a more suitable FA profile with higher amounts of saturated fatty acids and monounsaturated fatty acids (MUFAs) and a smaller polyunsaturated fatty acid (PUFA) component. Chlorella strains had a larger PUFA component and smaller MUFA component. The general trend in the FA composition of Chlorella strains was oleic > palmitic > α-linolenic = linoleic > eicosenoic > heptadecenoic > stearic acid. For Scenedesmus strains, the general trend was oleic > palmitic > linoleic > α-linolenic > stearic > eicosenoic > palmitoleic > heptadecenoic acid. The most promising strains with the highest lipid productivity and most suitable FA profiles were Scenedesmus sp. MACC 401, Scenedesmus soli MACC 721, and Scenedesmus ecornis MACC 714. Although Chlorella sp. MACC 519 had lower lipid productivity, the FA profile was good with a lower PUFA component compared to the other Chlorella strains analyzed and a low linolenic acid concentration.     

Biomass and oil content of Chlorella sp., Haematococcus sp., Nannochloris sp. and Scenedesmus sp. under mixotrophic growth conditions in the presence of technical glycerol

The growth of algae strains Chlorella sp., Haematococcus sp., Nannochloris sp. and Scenedesmus sp. under mixotrophic conditions in the presence of different concentrations of technical glycerol was investigated with the aim of increasing biomass growth and algae oil content. The highest concentration of lipid obtained in media with 5 g L^?1 glycerol for Chlorella sp., Scenedesmus sp., Nannochloris sp. and Haematococcus sp. was 17.77, 22.34, 27.55 and 34.22 % larger than during the autotrophic growth of these species. Increases in triacylglycerols of up to ten times was observed for Scenedesmus sp. under mixotrophic conditions (using 10 g L^?1 glycerol), whereas an increase of 2.28 times was found for Haematococcus sp. The content of saturated fatty acids of Scenedesmus, Chlorella, Haematococcus and Nannochloris was 67.11, 34.63, 23.39 and 24.23 %, and the amount of unsaturated fatty acids was 32.9, 65.06, 79.61 and 75.78 % of total fatty acids, respectively. Growth on technical glycerol of these strains with light produced higher biomass concentrations and lipid content compared with autotrophic growth. The fatty acid content of oils from these species suggests their potential use as biodiesel feedstock.     

Effects of different nitrogen, phosphorus, and iron concentrations and salinity on lipid production in newly isolated strain of the tropical green microalga, Scenedesmus dimorphus KMITL

The fatty acid composition, the effect of different concentrations of nitrogen (16.5-344 mg ?L^?1), phosphorus (9–45 mg? L^?1), iron (9–45 mg? L^?1) and salinity levels (0–20 psu) on lipid production in the green microalga Scenedesmus dimorphus KMITL, a new strain isolated from a tropical country, Thailand, were studied. The alga was isolated from a freshwater fish pond, and cultured in Chlorella medium by varying one parameter at a time. The main fatty acid composition of this strain was C16–C18 (97.52 %) fatty acids. A high lipid content was observed in conditions of 16.5 mg? L^?1-N, or 22 mg ?L^?1-P, or 45 mg ?L^?1-Fe, or 5 psu salinity, which accumulated lipids to 20.3?±?0.4, 19.4?±?0.2, 24.7?±?0.5, and 14.3?±?0.2 % of algal biomass, respectively. Increasing lipid content and lipid productivity was noted when the alga was cultured under high iron concentration and high salinity, as well as under reduced phosphorus conditions, whereas nitrogen limitation only resulted in an increased lipid content.     

Fatty acid composition and biological activities of Isochrysis galbana T-ISO,Tetraselmis sp. and Scenedesmus sp.: possible application in the pharmaceutical and functional food industries

Organic and water extracts of Isochrysis galbana T-ISO (=Tisochrysis lutea), Tetraselmis sp. and Scenedesmus sp. were evaluated for their antioxidant activity, acetylcholinesterase (AChE) inhibition, cytotoxicity against tumour cell lines, and fatty acids and total phenolic content (TPC). I. galbana T-ISO had the highest TPC (3.18 mg GAE g^?1) and radical scavenging activity, with an IC₅₀ value of 1.9 mg mL^?1 on the acetone extract. The extracts exhibited a higher ability to chelate Fe²⁺ than Cu²⁺, and the maximum Fe²⁺ chelating capacity was observed in the hexane extract of Scenedesmus sp. (IC₅₀=0.73 mg mL^?1) and Scenedesmus sp. (IC₅₀?=?0.73 mg mL^?1). The highest ability to inhibit AChE was observed in the water and ether extracts of Scenedesmus sp., with IC₅₀ values of 0.11 and 0.15 mg mL^?1, respectively, and in the water extract of I. galbana (IC₅₀?=?0.16 mg mL^?1). The acetone extract of I. galbana T-ISO significantly reduced the viability of human hepatic carcinoma HepG2 cells (IC₅₀?=?81.3 μg mL^?1) as compared to the non-tumour murine stromal S17 cell line, and displayed a selectivity index of 3.1 at the highest concentration tested (125 μg mL^?1). All species presented a highly unsaturated fatty acids profile. Results suggest that these microalgae, particularly I. galbana T-ISO, could be a source of biomolecules for the pharmaceutical industry and the production of functional food ingredients and can be considered as an advantageous alternative to several currently produced microalgae.     

Scenedesmus sp. NJ-1 isolated from Antarctica: a suitable renewable lipid source for biodiesel production

Microalgal lipids are promising alternative feedstocks for biodiesel production. Scenedesmus sp. NJ-1, an oil-rich freshwater microalga isolated from Antarctica, was identified to be a suitable candidate to produce biodiesel in this study. This strain could grow at temperatures ranging from 4 to 35?°C. With regular decrease in nitrate concentration in the medium, large quantities of triacylglycerols accumulated under batch culture conditions detected by thin layer chromatography and BODIPY 505/515 fluorescent staining. Scenedesmus sp. NJ-1 achieved the average biomass productivity of 0.105?g?l^?1?d^?1 (dry weight) and nearly the highest lipid content (35?% of dry cell weight) was reached at day 28 in the batch culture. Neutral lipids accounted for 78?% of total lipids, and C18:1 (n-9), C16:0 were the major fatty acids in total lipids, composing 37 and 20?% of total fatty acids of Scenedesmus sp. NJ-1 grown for 36?days, respectively. These results suggested that Scenedesmus sp. NJ-1 was a good source of microalgal oils for biodiesel production.     

Inorganic carbon and pH effect on growth and lipid productivity of Tetraselmis suecica and Chlorella sp (Chlorophyta) grown outdoors in bag photobioreactors

There has been considerable interest in cultivation of green microalgae (Chlorophyta) as a source of lipid that can alternatively be converted to biodiesel. However, almost all mass cultures of algae are carbon-limited. Therefore, to reach a high biomass and oil productivities, the ideal selected microalgae will most likely need a source of inorganic carbon. Here, growth and lipid productivities of Tetraselmis suecica CS-187 and Chlorella sp were tested under various ranges of pH and different sources of inorganic carbon (untreated flue gas from coal-fired power plant, pure industrial CO₂, pH-adjusted using HCl and sodium bicarbonate). Biomass and lipid productivities were highest at pH 7.5 (320?±?29.9 mg biomass L^?1 day^?1and 92?±?13.1 mg lipid L^?1 day^?1) and pH 7 (407?±?5.5 mg biomass L^?1 day^?1 and 99?±?17.2 mg lipid L^?1 day^?1) for T. suecica CS-187 and Chlorella sp, respectively. In general, biomass and lipid productivities were pH 7.5?>?pH 7?>?pH 8?>?pH 6.5 and pH 7?>?pH 7.5?=?pH 8?>?pH 6.5?>?pH 6?>?pH 5.5 for T. suecica CS-187 and Chlorella sp, respectively. The effect of various inorganic carbon on growth and productivities of T. suecica (regulated at pH?=?7.5) and Chlorella sp (regulated at pH?=?7) grown in bag photobioreactors was also examined outdoor at the International Power Hazelwood, Gippsland, Victoria, Australia. The highest biomass and lipid productivities of T. suecica (51.45?±?2.67 mg biomass L^?1 day^?1 and 14.8?±?2.46 mg lipid L^?1 day^?1) and Chlorella sp (60.00?±?2.4 mg biomass L^?1 day^?1 and 13.70?±?1.35 mg lipid L^?1 day^?1) were achieved when grown using CO₂ as inorganic carbon source. No significant differences were found between CO₂ and flue gas biomass and lipid productivities. While grown using CO₂ and flue gas, biomass productivities were 10, 13 and 18 %, and 7, 14 and 19 % higher than NaHCO₃, HCl and unregulated pH for T. suecica and Chlorella sp, respectively. Addition of inorganic carbon increased specific growth rate and lipid content but reduced biomass yield and cell weight of T. suecica. Addition of inorganic carbon increased yield but did not change specific growth rate, cell weight or content of the cell weight of Chlorella sp. Both strains showed significantly higher maximum quantum yield (F_v/F_m) when grown under optimum pH.     

Effects of stationary phase elongation and initial nitrogen and phosphorus concentrations on the growth and lipid-producing potential of Chlorella sp. HQ

Higher lipid production and nutrient removal rates are the pursuing goals for synchronous biodiesel production and wastewater treatment technology. An oleaginous alga Chlorella sp. HQ was tested in five different synthetic water, and it was found to achieve the maximum biomass (0.27 g L^?1) and lipid yield (41.3 mg L^?1) in the synthetic secondary effluent. Next, the effects of the stationary phase elongation and initial nitrogen (N) and phosphorus (P) concentrations were investigated. The results show that the algal characteristics were affected apparently under different N concentrations but not P, which were verified by Logistic and Monod models. At the early stationary phase, the algal biomass, lipid and triacylglycerols (TAGs) yields, and P removal efficiency increased and reached up to 0.19 g L^?1, 46.7 mg L^?1, 14.3 mg L^?1, and 94.3 %, respectively, but N removal efficiency decreased from 86.2 to 26.8 % under different N concentrations. And the largest TAGs yield was only 6.4 mg L^?1 and N removal efficiency was above 71.1 % under different P concentrations. At the late stationary phase, the maximal biomass, lipid and TAGs yields, and P removal efficiencies primarily increased as the initial N and P concentrations increase and climbed up to 0.49 g L^?1, 99.2 mg L^?1, 54.0 mg L^?1, and 100.0 %, respectively. It is concluded that stationary phase elongation is of great importance and the optimal initial N/P ratio should be controlled between 8/1 and 20/1 to serve Chlorella sp. HQ for better biodiesel production and secondary effluent purification.     

Arsenic Resistance and Bioaccumulation of an Indigenous Bacterium Isolated from Aquifer Sediments of Datong Basin,Northern China

To obtain bacteria with arsenic accumulation potential that can be used to remove arsenic from contaminated waters, experiments were made to investigate the tolerance and accumulation to arsenic of an indigenous bacterium XZM002 isolated from aquifer sediments of Datong Basin, northern China. The results showed that strain XZM002 belongs to the genus Bacillus and has evolved defense mechanisms to reduce arsenic injury: the change of cellular shape from initial rod to oval and then to round with increment of arsenic toxicity. The effect of arsenate or arsenite on the bacterial growth was also investigated. Results showed that growth of the strain was inhibited under As(III) and high concentration As(V) (over 1200 μg l^?1) conditions in the first 2 days and promoted under low concentration As(V) (under 400 μg l^?1) condition. Its arsenic bioaccumulation potential was surveyed by monitoring the concentration changes of total arsenic and arsenic speciation in the medium and in the cytoplasm, and those of total arsenic on the membrane. Methylated arsenic species were not detected throughout the experiment. The results indicated that 11.5% of arsenic was removed from liquid medium into the bacterial cells and 9.22% of As(V) in the medium was transformed gradually to As(III) during 4 d of incubation. Approximately 80% of the total accumulated arsenic was adsorbed onto the membrane instead of into cytoplasm; and the arsenic accumulation almost approached saturation after incubation for 72 h.     

Effects of Initial Phosphorus Concentration and Light Intensity on Biomass Yield per Phosphorus and Lipid Accumulation of Scenedesmus sp. LX1

Phosphorus has been considered as one of the most important limiting resources of large-scale production of microalgal biofuel. The approaches to increase biomass yield per phosphorus, along with the lipid accumulation properties of Scenedesmus sp. LX1, were investigated in this study. It was found that practical biomass yield per phosphorous was reduced with the increase of initial phosphorus (P) concentration, but increased with light intensity. The highest biomass yield per P of 4,500 kg-biomass/kg-P was achieved at initial phosphorus concentration of 0.05 mg?·?L^?1 under the light intensity of 320 μmol photon?·?m^?2?·?s^?1. Furthermore, the lipid content per biomass and triacylglycerols (TAGs) content per lipid were found to be positively correlated to biomass yield per P. With the biomass yield increased from 2,800 kg-biomass/kg-P to 4,500 kg-biomass/kg-P, the lipid content per microalgal biomass and TAG content per lipid increased from 18.7 % to 35.0 % and from 69.5 % to 83.0 %. These results suggested a possible approach to achieve high biomass production and high lipid content simultaneously.     

Low-cost cultivation of <Emphasis Type="Italic">Scenedesmus</Emphasis> sp. with filtered anaerobically digested piggery wastewater: biofuel production and pollutant remediation

A laboratory study was conducted on biomass and lipid production by Scenedesmus sp. and the removal of total nitrogen (TN) and total phosphorus (TP) from filtered anaerobically digested piggery wastewater. The dry weight (DW), lipid content and productivity, total nitrogen, and total phosphorus removal rate were assessed in five media: modified soil extract (MSE) medium, 5 % anaerobic digested wastewater (ADWW), 10 % ADWW, 15 % ADWW, and 5 % ADWW supplemented with NaNO₃. The highest biomass productivity appeared in the 15 % ADWW group, which was 20.4 % higher than MSE group. The highest lipid content was found in the 5 % ADWW group (31.60 %), while the highest lipid productivity was in the 10 % ADWW group (27.01 mg L^?1 day^?1). Compared with the 5 % ADWW group, the 5 % ADWW group supplemented with NaNO₃ had a similar biomass amount but lower lipid content and productivity. The fatty acids percentage of Scenedesmus sp. showed a slight difference in different media, but with the four dominant fatty acids (C16:0, C18:1, C18:2, C18:3) accounting for 87 % of the total fatty acids, suggests that Scenedesmus sp. in ADWW medium was no different than MSE in terms of lipid composition and content. TN removal rates were 82.85, 82.51, 85.85, 91.28, and 78.71 % in groups 1 to 5, and TP removal rates were 53.05, 88.53, 87.77, 88.72, and 80.64 %. Our experiment also shows the feasibility of using ADWW as a substitute of all the elements of MSE medium except for carbon, which would significantly reduce the costs of microalgal culture.     

Influence of culture age on the phytochemical content and pharmacological activities of five Scenedesmus strains

Five axenic Scenedesmus strains (MACC-411, MACC-422, MACC-493, MACC-720, and MACC-727) were cultured and harvested after 5 and 10 days in culture. Using colorimetric methods, the concentrations of total phenolic, condensed tannin, and iridoids in 50 % methanol extracts from both 5- and 10-day-old cultures were quantified. Different solvent extracts from the strains were also tested for antioxidant, acetylcholinesterase inhibitory (AChEI), and antimicrobial activities using various in vitro test systems. Phenolic content was highest (3.6?±?0.42 mg GAE g^?1 DW) in 10-day-old MACC-727. This was approximately fourfold and significantly higher than in the 5-day-old cultures of MACC-727. Among the tested Scenedesmus strains, 5-day-old MACC-411 had the highest iridoid content (3.4?±?0.3 mg HE g^?1 DW), and this was significantly higher than the level detected in the 10-day-old MACC-411. Scenedesmus strains showed better antioxidant potential in the β-carotene–linoleic acid model compared to the DPPH free radical scavenging assay. The AChEI activity (IC₅₀?μg mL^?1) in all strains (besides MACC-422) was higher in 10-day-old cultures compared to the 5-day-old cultures. Although a broad-spectrum of antibacterial activity was observed, the tested microalgae strains demonstrated varying degrees of antimicrobial potential depending on the harvest time, strain-type, and extracting solvent. Thus, the Scenedesmus strain and time of harvest played a significant role in determining their phytochemical content and resultant pharmacological activity. The promising bioactivity in the tested Scenedesmus strains indicates their potential as possible sources of novel/alternative antioxidants and AChE inhibitors.     

Polyhydroxyalkanoate biosynthesis and simultaneous remotion of organic inhibitors from sugarcane bagasse hydrolysate by Burkholderia sp.

Burkholderia sp. F24, originally isolated from soil, was capable of growth on xylose and removed organic inhibitors present in a hemicellulosic hydrolysate and simultaneously produced poly-3-hydroxybutyrate (P3HB). Using non-detoxified hydrolysate, Burkholderia sp. F24 reached a cell dry weight (CDW) of 6.8 g L^?1, containing 48 % of P3HB and exhibited a volumetric productivity (P_P3HB) of 0.10 g L^?1 h^?1. Poly-3-hydroxybutyrate-co-3-hydroxyvalerate copolymers (P3HB-co-3HV) were produced using xylose and levulinic acid (LA) as carbon sources. In shake flask cultures, the 3HV content in the copolymer increased from 9 to 43 mol% by adding LA from 1.0 to 5.0 g L^?1. In high cell density cultivation using concentrated hemicellulosic hydrolysate F24 reached 25.04 g L^?1 of CDW containing 49 % of P3HB and P_P3HB of 0.28 g L^?1 h^?1. Based on these findings, second-generation ethanol and bioplastics from sugarcane bagasse is proposed.     

Screening of plant growth-promoting traits in arsenic-resistant bacteria isolated from the rhizosphere of soybean plants from Argentinean agricultural soil

Aims

The purpose of this study was to investigate plant-growth promoting traits in native and arsenic (As) highly-resistant bacterial strains isolated from the rhizosphere of soybean (Glycine max) plants grown in an Argentinean agricultural field.

Methods

Determination of MICs (Minimum inhibitory concentration) was carried out on solid media supplemented with arsenite (As 3+) or arsenate (As 5+). Morphological, cultural, physiological, biochemical and molecular characterization, and in vitro determination of plant growth promoting (PGP) properties of As resistant isolates were carried out. Arsenic in soil samples was determined by ICP-OES while residual arsenic on post-removal culture medium and accumulation in cells were estimated by GF-AAS after wet acid digestion.

Results

Isolated strains included γ-proteobacteria such as Enterobacter sp. and Pseudomonas sp., and actinobacteria as Rhodococcus sp. All bacterial strains grew in presence of very high arsenite -over 24?mM- and arsenate –over 400?mM- concentrations. Pseudomonas sp. strains presented simultaneously several in vitro PGP traits, although Rhodococcus erythropolis AW3 did not display PGP traits. However, R. erythropolis AW3 was the most As resistant strain and removed and accumulated the greatest amounts of the metalloid.

Conclusion

The presence of As resistant and plant-growth promoting bacterial strains in the rhizosphere of Glycine max, in arsenic containing agricultural soil, suggest that they could potentially play an important role in plant-growth promotion in stressed conditions. These strains were able to remove and accumulate As from liquid media, thus they could be beneficial for sustainable crop production.     

INFLUENCE OF SOIL PROPERTIES AND PHOSPHATE ADDITION ON ARSENIC UPTAKE FROM POLLUTED SOILS BY VELVETGRASS (HOLCUS LANATUS)

Four kinds of soil material were used in a pot experiment with velvetgrass (Holcus lanatus). Two unpolluted soils: sand (S) and loam (L) were spiked with sodium arsenite (As III) and arsenate (As V), to obtain total arsenic (As) concentrations of 500 mg As kg^?1. Two other soils (ZS I, ZS III), containing 3320 and 5350 mg As kg^?1, were collected from Zloty Stok where gold and arsenic ores were mined and processed for several centuries. The effects of phosphate addition on plants growth and As uptake were investigated. Phosphate was applied to soils in the form of NH₄H₂PO₄ at the rate 0.2 g P/kg. Average concentrations of arsenic in the shoots of velvetgrass grown in spiked soils S and L without P amendment were in the range 18–210 mg As kg^?1 d.wt., whereas those in plants grown on ZS I and ZS II soils were considerably lower, and varied in the range 11–52 mg As kg^?1 d.wt. The addition of phosphate caused a significant increase in plant biomass and therefore the total amounts of As taken up by plants, however, the differences in As concentrations in the shoots of velvetgrass amended and non-amended with phosphate were not statistically significant.     

Promoting effects of organic medium supplements on the micropropagation of promising ornamental Daphne species (Thymelaeaceae)

Three Daphne species (Thymelaeaceae) were propagated in vitro using media enriched with natural ingredients including coconut water, pineapple pulp, arabinogalactan, chitosan, and conditioned medium containing exudates of the green alga Desmodesmus subspicatus. High vigor of proliferative shoots and enhanced rooting efficiency were obtained. The propagation rate for shoot cultures of Daphne caucasica and Daphne tangutica increased significantly when cultured in the presence of 10 ml?L^?1 coconut water or 10 ml?L^?1 pineapple pulp. Addition of 10 ml?L^?1 pineapple pulp, 10 ml?L^?1 coconut water, or 20% conditioned medium to the culture medium stimulated organogenesis in D. caucasica. The percentage of rooted shoots in this difficult-to-root species reached 80% in enriched medium. Daphne jasminea plants rooted efficiently on media without growth regulators but supplemented with 10 ml?L^?1 pineapple pulp or 10 ml?L^?1 coconut water. Plants of D. caucasica and D. jasminea were successfully acclimatized to greenhouse conditions. Biochemical evaluation of pineapple pulp using thin-layer chromatography revealed the absence of natural auxins. However, the low-molecular-weight fraction (<500 Da) obtained via dialysis significantly stimulated rhizogenesis in each species tested.     

Acute Toxicity of Arsenic under Different Temperatures and Salinity Conditions on the White Shrimp Litopenaeus vannamei

The aim of this study was to determine acute toxicity in the post larvae of the white shrimp Litopenaeus vannamei after 96 h of exposure to dissolved arsenic under three different temperatures and salinity conditions. Recent reports have shown an increase in the presence of this metalloid in coastal waters, estuaries, and lagoons along the Mexican coast. The white shrimp stands out for its adaptability to temperature and salinity changes and for being the main product for many commercial fisheries; it has the highest volume of oceanic capture and production in Mexican shrimp farms. Lethal concentrations (LC₅₀–96 h) were obtained at nine different combinations (3?×?3 combinations in total) of temperature (20, 25, and 30 °C) and salinity (17, 25, and 33) showing mean LC₅₀–96 h values (±standard error) of 9.13?±?0.76, 9.17?±?0.56, and 6.23?±?0.57 mgAs?L^?1(at 20 °C and 17, 25, and 33 salinity); 12.29?±?2.09, 8.70?±?0.82, and 8.03?±?0.59 mgAs?L^?1 (at 25 °C and 17, 25, and 33 salinity); and 7.84?±?1.30, 8.49?±?1.40, and 7.54?±?0.51 mgAs?L^?1 (at 30 °C and 17, 25, and 33 salinity), respectively. No significant differences were observed for the optimal temperature and isosmotic point of maintenance (25 °C–S 25) for the species, with respect to the other experimental conditions tested, except for at 20 °C–S 33, which was the most toxic. Toxicity under 20 °C–S 33 conditions was also higher than 25 °C–S 17 and 20 °C (S 17 or 25). The least toxic condition was 25 °C–S 17. All this suggests that the toxic effect of arsenic is not affected by temperature changes; it depends on the osmoregulatory pattern developed by the shrimp, either hyperosmotic at low salinity or hiposmotic at high salinity, as observed at least on the extreme salinity conditions here tested (17 and 33). However, further studies testing salinities near the isosmotic point (between 20 and 30 salinities) are needed to clarify these mechanisms.