Effect of the polycyclic aromatic hydrocarbon phenanthrene on root exudation of Sorghum bicolor (L.) Moench

The objective of this work was to study the effect of two concentrations (10 and 100 mg kg⁻¹) of phenanthrene, a ubiquitous polycyclic aromatic hydrocarbon (PAH), on root exudation of the remediating plant Sorghum bicolor (L.) Moench under controlled conditions in a pot experiment. It was found that the phenanthrene concentration of 10 mg kg⁻¹ did not cause significant effects on plant survival and growth but had little stimulating effect on carbohydrate exudation. The contamination with phenanthrene at 100 mg kg⁻¹ inhibited accumulation of plant shoot and root biomass, decreasing the carboxylic acid, carbohydrate, and amino acid amounts released by sorghum root into the rhizosphere. However, root exudation per unit of root surface was not changed significantly with increasing phenanthrene concentration. There were no differences in qualitative composition of root exudates under the influence of PAH were found. The observed alterations in the ratio between the main root-exuded components are assumed to manifest adaptive alterations occurring in the plant as a response to pollutant stress. The activity of three oxidoreductases (oxidase, peroxidase, and tyrosinase) released by sorghum roots was clearly progressive to the increasing phenanthrene concentration in the substrate. Under the influence of phenanthrene, the population of phenanthrene-degrading microorganisms in sorghum root zone increased, and their share in the total number of culturable heterotrophs increased as well. The main promotional factor was the pollutant; however, the stimulating effect of the plant root exudates was also involved. The increased pollutant-degrading microbial population and activity of the extracellular root enzymes are presumed to be important for the rhizodegradation of PAH.     

Biochemical and physiological peculiarities of the interactions between <Emphasis Type="Italic">Sinorhizobium meliloti</Emphasis> and <Emphasis Type="Italic">Sorghum bicolor</Emphasis> in the presence of phenanthrene

The effect of phenanthrene, a polycyclic aromatic hydrocarbon (PAH) at concentrations of 0, 10, and 100 mg/kg and the bacterium Sinorhizobium meliloti P221 on root exudation of Sorghum bicolor L. Moench was studied in laboratory vegetative experiments. Inoculation of the bacterium promoted plant resistance to the pollutant stress and increased their acclimation rate and biomass formation. The ability of this microorganism to produce a phytohormone, indolyl-3-acetic acid, and to degrade phenanthrene, resulted in morphological changes of the plant root system and in the changed intensity of root exudation. In root exudates of sorghum, enzyme activities towards the metabolites formed during microbial degradation of PAH were revealed, which is indicative of a direct involvement of plants in PAH degradation in the rhizosphere as well as of the coupled plant-microbial metabolism in the course of xenobiotic degradation in the root zone. In phenanthrene-contaminated soil, sorghum was found to support selectively the development of the S. meliloti P221 population.     

Effect of ecological engineering on the nutrient content of surface sediments in Lake Taihu, China

Ecological engineering was carried out in Meiliang Bay of Lake Taihu beginning in 2003 in order to improve water quality. There were two main objectives: to improve the growth environment for macrophytes, and to restore macrophyte assemblages. We examined surface sediments once per month beginning in April 2005 to study the response of sediment nutrient content to the ecological engineering. Average total nitrogen (TN) and total phosphorus (TP) concentrations in the surface sediments were 7043 and 1370 mg kg⁻¹, respectively, in May 2005, while after 1 year, TN concentration was reduced to 2929 mg kg⁻¹ and TP concentration was reduced to 352 mg kg⁻¹. We conclude that ecological engineering can lower the nutrient content in surface sediments when it is used to improve water quality.     

Microcosm assays and Taguchi experimental design for treatment of oil sludge containing high concentration of hydrocarbons

Microcosm assays and Taguchi experimental design was used to assess the biodegradation of an oil sludge produced by a gas processing unit. The study showed that the biodegradation of the sludge sample is feasible despite the high level of pollutants and complexity involved in the sludge. The physicochemical and microbiological characterization of the sludge revealed a high concentration of hydrocarbons (334,766 ± 7001 mg kg⁻¹ dry matter, d.m.) containing a variety of compounds between 6 and 73 carbon atoms in their structure, whereas the concentration of Fe was 60,000 mg kg⁻¹ d.m. and 26,800 mg kg⁻¹ d.m. of sulfide. A Taguchi L₉ experimental design comprising 4 variables and 3 levels moisture, nitrogen source, surfactant concentration and oxidant agent was performed, proving that moisture and nitrogen source are the major variables that affect CO₂ production and total petroleum hydrocarbons (TPH) degradation. The best experimental treatment yielded a TPH removal of 56,092 mg kg⁻¹ d.m. The treatment was carried out under the following conditions: 70% moisture, no oxidant agent, 0.5% of surfactant and NH₄Cl as nitrogen source.     

Dynamics of microbial community during bioremediation of phenanthrene and chromium(VI)-contaminated soil microcosms

The combined effect of phenanthrene and Cr(VI) on soil microbial activity, community composition and on the efficiency of bioremediation processes has been studied. Biometer flask systems and soil microcosm systems contaminated with 2,000 mg of phenanthrene per kg of dry soil and different Cr(VI) concentrations were investigated. Temperature, soil moisture and oxygen availability were controlled to support bioremediation. Cr(VI) inhibited the phenanthrene mineralization (CO₂ production) and cultivable PAH degrading bacteria at levels of 500–2,600 mg kg⁻¹. In the bioremediation experiments in soil microcosms the degradation of phenanthrene, the dehydrogenase activity and the increase in PAH degrading bacteria counts were retarded by the presence of Cr(VI) at all studied concentrations (25, 50 and 100 mg kg⁻¹). These negative effects did not show a correlation with Cr(VI) concentration. Whereas the presence of Cr(VI) had a negative effect on the phenanthrene elimination rate, co-contamination with phenanthrene reduced the residual Cr(VI) concentration in the water exchangeable Cr(VI) fraction (WEF) in comparison with the soil microcosm contaminated only with Cr(VI). Clear differences were found between the denaturing gradient gel electrophoresis (DGGE) patterns of each soil microcosm, showing that the presence of different Cr(VI) concentrations did modulate the community response to phenanthrene and caused perdurable changes in the structure of the microbial soil community.     

Treatment of an artificial sulphide containing wastewater in subsurface horizontal flow laboratory-scale constructed wetlands

In general, treatment wetlands seem to be a potential method of tackling the sulphide problem of post-treatment of anaerobic digester effluents.Because of insufficient practical experience and lack of knowledge of sulphide removal, sulphur transformation was investigated, particularly in horizontal subsurface flow constructed wetlands (depth of 35 cm) under laboratory-scale conditions with artificial wastewater.The plants affected a clear stimulation of the sulphide and ammonia removal rates. Sulphide concentration in the range of 1.5–2.0 mg l⁻¹ was tolerated by the plants and completely removed in the planted model wetlands; sulphide concentration of >2.0 mg l⁻¹ caused instabilities in sulphide and nitrogen removal. Area-specific sulphide removal rates of up to 94 mg sulphide m⁻² d⁻¹ were achieved in the planted beds at hydraulic retention times of 2.5 d. Sulphate affected the sulphide removal. While in the unplanted control bed an almost stable removal in the range of 150–300 mg N m⁻² d⁻¹ was observed variations of hydraulic retention time, sulphide and sulphate concentrations influenced the ammonia removal rate within the planted beds in a broader range (600–1400 mg N m⁻² d⁻¹).These results showed that nitrification, sulphide oxidation, denitrification and sulphate reduction can occur simultaneously in the rhizosphere of treatment wetlands caused by dynamic redox gradients (aerobic–anaerobic) conditions.     

Tolerance and remedial function of rooted submersed macrophyte Vallisneria spiralis to phenanthrene in freshwater sediments

Tolerance and remedial function of submersed macrophyte Vallisneria spiralis to phenanthrene in freshwater sediments were investigated by manipulating initial phenanthrene concentrations in sediments from 8 to 80 mg kg⁻¹ dry sediment. The biomass growth of V. spiralis on phenanthrene-spiked sediments was not adversely affected until initial phenanthrene concentrations in sediments increased to 80 mg kg⁻¹ dry sediment. V. spiralis might evolve adaptive mechanisms to toxic contaminants in sediment, and then could change the growth patterns in order to decrease the toxicity on its growth. The removal efficiencies of phenanthrene from the planted sediments were 18% higher than those from the sediments without plant even under an initial phenanthrene concentration of 80 mg kg⁻¹ dry sediments. The enhanced removal of phenanthrene in sediments by the plant might be achieved mainly by the synergism between plant roots and microbes in the rhizosphere.     

Biomass and photosynthetic productivity of water hyacinth (Eichhornia crassipes) as affected by nutrient supply and mirid (Eccritotarus catarinensis) biocontrol

The biological control of water hyacinth is affected by water nitrogen and phosphorus content and this was investigated experimentally at five levels of nutrient supply by measuring plant photosynthetic and growth responses, and mirid reproduction and herbivory of nutrient treated plants. Low nitrogen (2–0.2 mg L⁻¹) and phosphorus (0.2–0.01 mg L⁻¹) supply decreased hyacinth photosynthesis, growth and biomass accumulation relative to plants supplied 200 mg L⁻¹ N and 20 mg L⁻¹ P. This effect depended more on nitrogen supply than phosphorus supply. Chlorophyll fluorescence showed that the photosynthetic light reactions of low nutrient plants were affected and leaves had decreased chlorophyll content, density of functional photosystems II and dissipated a greater proportion of absorbed energy as heat. Gas exchange parameters showed reduced carboxylation efficiency, rates of RuBP regeneration and light saturated photosynthetic rates, but not quantum yields. Effects on photosynthesis translated into lower plant dry biomass. Mirid herbivory exacerbated the effects of low nutrients noted for chlorophyll fluorescence, gas exchange parameters and biomass accumulation, however, these effects were not always significant and there was no obvious correlation between the level of nutrients supplied and the effect of mirid herbivory. Low nutrient supply did, however, affect mirid performance reducing the number of adult insects, nymphs and herbivory intensity suggesting that in the long-term mirid populations would be significantly affected by water nutrient status.     

Methyl jasmonate effect on diterpenoid accumulation in Salvia sclarea hairy root culture in shake flasks and sprinkle bioreactor

Hairy root cultures of Salvia sclarea were grown in shake flasks and 10 L nutrient sprinkle bioreactor, running for 30 days and the effects of methyl jasmonate (MJ) on their growth and capacity to accumulate diterpenoids were measured. We found that MJ concentration and exposure time to the elicitor were factors that strongly affected the diterpenoid production. The highest diterpenoid accumulation (67.5 ± 7.1 mg g⁻¹ dry weight, calculated as a sum of ferruginol, salvipisone, aethiopinone and 1-oxoaethiopinone) without reduction of biomass, was achieved when the 23-day-old hairy roots in bioreactor culture were exposed to 125 μM MJ for 7 days. The roots produced 9 and 3.8 times as much aethiopinone (40 ± 5.9 mg g⁻¹ dry weight) and salvipisone (12.6 ± 0.4 mg g⁻¹ dry weight), respectively, as roots cultured in shake flasks. Our results imply that cultivation of S. sclarea hairy roots in sprinkle bioreactor after elicitation with MJ may be valuable to enhance production of the bioactive diterpenoids.     

Dissolved phosphorus concentrations and sediment interactions in effluent–dominated Ozark streams

Phosphorus (P) loads from point sources have a significant influence on dissolved P concentrations in streams and sediment-water column dynamics. The goal of this study was to quantify dissolved P concentrations and sediment-P interactions in Ozark (USA) headwater streams with high point source P loads. Specifically, the objectives were to: (1) compare soluble reactive P (SRP) upstream and downstream from wastewater treatment plant (WWTP) effluent discharges; (2) examine longitudinal gradients in SRP downstream from WWTPs; (3) evaluate the effect of WTTP P inputs on sediment-water column P equilibrium and sediment exchangeable P. Water and sediment samples were collected, extracted and analyzed from July 2002 through June 2003 at these Ozark streams. Mean SRP concentrations in the select Ozark streams were significantly greater downstream from effluent discharges (0.08–2.10 mg L⁻¹) compared to upstream (0.02–0.12 mg L⁻¹). Effluent discharge from the WWTPs increased equilibrium concentrations between stream sediments and the water column; mean sediment equilibrium P concentration (EPC₀) was between 0.01–0.07 mg L⁻¹ upstream from WWTP and the increase downstream was proportional to that observed in water column SRP. Sediment exchangeable P (EXP) was greater downstream from the effluent discharges (0.3–6.8 mg kg⁻¹) compared to upstream (0.03–1.4 mg kg⁻¹), representing a substantial transient storage of P inputs from WWTPs. Furthermore, P was generally not retained in these stream reaches when dilution was considered using a hydrologic tracer and was released in one stream reach where effluent P concentrations decreased over the study period. Thus, the effect of the WWTPs was profound in these streams increasing water column and sediment-bound P, and also reducing the ability of these stream reaches to retain P. In P-enriched streams, effluent P discharges likely regulate sediment and aqueous phase P equilibrium and sediment bioavailable P, not the sediments.     

Spatial and temporal variation in citrate and malate exudation and tissue concentration as affected by P stress in roots of white lupin

Exudation of carboxylates represents one the most efficient strategies used by P-starved white lupin (Lupinus albus L.) to acquire phosphorus from sparingly soluble sources. This exudation occurs through proteoid root clusters, with citrate being the predominant organic acid released. The occasional detection of malate in whole root exudates suggests that this acid would also be released, but from tissues other than root clusters. To investigate the spatial and temporal pattern of exudation, citrate and malate exudation and concentration were measured in whole roots and root sections of white lupin, from seedling emergence to plant senescence due to P starvation. Both organic acids were detected in whole root exudates of P-stressed plants, and they were released at similar rates throughout the experiment. Malate was predominantly exuded from apices of both seedling taproots and proteoid roots, whereas citrate exudation was restricted to proteoid root clusters. Studies directed to address the association between carboxylate exudation and concentration in proteoid root clusters showed a non-linear response for citrate, within the range of 7 to 23 mol g^–1 fresh weight. This association was further assessed by altering citrate concentration in the whole root. Adding P to 24-day-old P-starved plants reduced citrate concentration and exudation to the level of the control P-fed plants, demonstrating that citrate exudation and concentration are associated. Malate exudation and concentration did not correlate significantly. Results indicate that citrate release by P-starved white lupin would occur whenever a certain threshold of citrate concentration is attained, and that the sites, the rates and the span of transient exudation depend on the physiological age of the tissue.     

Colonization on Root Surface by a Phenanthrene-Degrading Endophytic Bacterium and Its Application for Reducing Plant Phenanthrene Contamination

A phenanthrene-degrading endophytic bacterium, Pn2, was isolated from Alopecurus aequalis Sobol grown in soils contaminated with polycyclic aromatic hydrocarbons (PAHs). Based on morphology, physiological characteristics and the 16S rRNA gene sequence, it was identified as Massilia sp. Strain Pn2 could degrade more than 95% of the phenanthrene (150 mg·L⁻¹) in a minimal salts medium (MSM) within 48 hours at an initial pH of 7.0 and a temperature of 30°C. Pn2 could grow well on the MSM plates with a series of other PAHs, including naphthalene, acenaphthene, anthracene and pyrene, and degrade them to different degrees. Pn2 could also colonize the root surface of ryegrass (Lolium multiflorum Lam), invade its internal root tissues and translocate into the plant shoot. When treated with the endophyte Pn2 under hydroponic growth conditions with 2 mg·L⁻¹ of phenanthrene in the Hoagland solution, the phenanthrene concentrations in ryegrass roots and shoots were reduced by 54% and 57%, respectively, compared with the endophyte-free treatment. Strain Pn2 could be a novel and useful bacterial resource for eliminating plant PAH contamination in polluted environments by degrading the PAHs inside plants. Furthermore, we provide new perspectives on the control of the plant uptake of PAHs via endophytic bacteria.     

Biodegradation of Methyl red by Galactomyces geotrichum MTCC 1360

Galactomyces geotrichum MTCC 1360 can decolorize triphenylmethane, azo and reactive high exhaust textile dyes. At shaking condition this strain showed 100% decolorization of a toxic azo dye Methyl red (100 m gl⁻¹) within 1 h in deionized water at 30 °C. The degradation of Methyl red was possible through a broad pH (3–12) and temperature (5–50 °C) range. Glucose and mycelium concentration had increased the decolorization rate, but the addition of 1 gl⁻¹ molasses in deionized water made decolorization possible in only 10 min. Induction in the NADH–dichloro phenol indophenol (NADH–DCIP) reductase, Malachite green reductase, laccase and lignin peroxidase (Lip) activities were observed in the cells obtained after complete decolorization, showing that there is direct involvement in the degradation of Methyl red. The absence of N-N′-dimethyl-p-phenylenediamine (DMPD) in 5 °C, 2-aminobenzoic acid (ABA) in 50 °C and both the compounds in 30 °C sample have shown the differences in the metabolic fate of Methyl red at different temperatures. The untreated dye at 300 mg l⁻¹ concentration showed 88% germination inhibition in Sorghum bicolor, whereas it was 72% in Triticum aestivum. There was no germination inhibition for both the plants by Methyl red metabolites at 300 mg l⁻¹ concentration.

The scientific relevance of the paper

The azo dye Methyl red (100 mg l⁻¹) was decolorized by G. geotrichum MTCC 1360 within 1 h at shaking condition in deionized water. This organism could decolorize Methyl red at wide pH and temperature ranges. Decolorization time was reduced to 10 min by the addition of molasses to deionized water. There was induction in laccase and Lip, NADH–DCIP reductase and Malachite green reductase activities. The metabolic fate of Methyl red changes with temperature which can be evidenced by the formation of 2-ABA at 5 °C, N-N′-DMPD at 50 °C and both the compounds were absent at 30 °C. Phytotoxicity showed that metabolites of dye had induced shoot and root length of both the tested plants.     

High-performance liquid chromatographic method for determination of DDT and its degradation products in rat plasma, liver and brain: validation and application to a pharmacokinetic study

A sensitive and reliable high-performance liquid chromatographic (HPLC) method, using a solid-phase extraction (SPE), was established and validated for determination of p,p′-DDT [1,1,1-trichloro-2,2-bis(4-chlorophenyl)ethane] and its metabolite p,p′-DDE [1,1-(2,2-dichloroethanylidene)-bis(4-chlorobenzene)] in rat plasma, liver and brain. After being diluted with water, plasma, liver and brain samples were applied to a solid-phase extraction C₁₈ cartridge. The extraction containing p,p′-DDT and p,p′-DDE from the cartridge were cleaned-up using a Florisil Sep-Pak cartridge. The samples were analyzed by HPLC using UV detection at 238 nm. The limit of detection for p,p′-DDT and p,p′-DDE was 0.1 mg kg⁻¹ liver or brain and 0.1 mg l⁻¹ plasma. For six replicate samples at 40, 4 and 0.2 mg kg⁻¹, intra-day precision values were within 4.9% for plasma, 6.4% for liver, and 9.7% for brain. Inter-day precision values at 4 mg kg⁻¹ were within 8.2% for plasma and tissues. The method performances were shown to be selective for p,p′-DDT and p,p′-DDE, and linear over the range 0.04–12 mg kg⁻¹ (mg l⁻¹ for plasma). The absolute recoveries of p,p′-DDT and p,p′-DDE in rat plasma and tissues were over 92%. The method was proved to be applicable to the pharmacokinetic study of DDT in rats after a single oral administration.     

Significant enhancement of oleanolic acid accumulation by biotic elicitors in cell suspension cultures of Calendula officinalis L.

The effects of elicitors on cell growth and oleanolic acid (OA) accumulation in shaken cell suspension cultures of Calendula officinalis were investigated. Elicitors were added individually at various concentrations to 5-day-old cell cultures and their effects monitored at 24 h intervals for 4 days. Different effects on OA accumulation were observed depending on the day of treatment. Jasmonic acid was the most efficient elicitor. After 72 h of treatment with 100 μM JA, the intracellular content of OA reached its maximum value (0.84 mg g⁻¹ DW), which was 9.4-fold greater than that recorded in an untreated control cultures. The addition of chitosan at 50 mg l⁻¹ produced a 5-fold enhancement of OA accumulation (0.37 mg g⁻¹ DW) after 48 h of treatment. Treatment with yeast extract at 200 mg l⁻¹ for 96 h or with pectin at 2 mg l⁻¹ for 48 h produced identical cellular levels of OA (0.22 mg g⁻¹ DW). Lastly, 48 h elicitation with homogenate of the fungus Trichoderma viride produced a 1.8-fold increase in oleanolic acid content (0.12 mg g⁻¹ DW). In addition to significantly stimulating OA accumulation and its secretion into the culture medium, the elicitors also caused slight inhibition of cell growth.     

Interaction of Pb and Cd with gum kondagogu (Cochlospermum gossypium): A natural carbohydrate polymer with biosorbent properties

Gum kondagogu (Cochlospermum gossypium), an exudates tree gum from India was explored for its potential to decontaminate toxic metals (Pb²⁺ and Cd²⁺). Optimum biosorption of metals were determined by investigating the contact time, pH, initial concentration of metal ions and biosorbent dose at 25 ± 2 °C. The maximum metal biosorption capacity for gum kondagogu was observed for Pb²⁺ (48.52 mg g⁻¹) and Cd²⁺ (47.48 mg g⁻¹) as calculated by Langmuir isotherm model. Kinetic studies showed that the biosorption rates could be described by pseudo-second-order expression. The metal interactions with biopolymer were assessed by FT-IR, SEM–EDXA and XPS analysis. Results based on these techniques suggest that mechanism of metal binding by the biopolymer involves micro-precipitation, ion-exchange and metal complexation.     

In vitro propagation of plant virus using different forms of plant tissue culture and modes of culture operation

Plant virus accumulation was investigated in vitro using three different forms of plant tissue culture. Suspended cells, hairy roots and shooty teratomas of Nicotiana benthamiana were infected with tobacco mosaic virus (TMV) using the same initial virus:biomass ratio. Viral infection did not affect tissue growth or morphology in any of the three culture systems. Average maximum virus concentrations in hairy roots and shooty teratomas were similar and about an order of magnitude higher than in suspended cells. Hairy roots were considered the preferred host because of their morphological stability in liquid medium and relative ease of culture. The average maximum virus concentration in the hairy roots was 0.82 ± 0.14 mg g⁻¹ dry weight; viral coat protein represented a maximum of approximately 6% of total soluble protein in the biomass. Virus accumulation in hairy roots was investigated further using different modes of semi-continuous culture operation aimed at prolonging the root growth phase and providing nutrient supplementation; however, virus concentrations in the roots were not enhanced compared with simple batch culture. The relative infectivity of virus in the biomass declined by 80–90% during all the cultures tested, irrespective of the form of plant tissue used or mode of culture operation. Hairy root cultures inoculated with a transgenic TMV-based vector in batch culture accumulated green fluorescent protein (GFP); however, maximum GFP concentrations in the biomass were relatively low at 39 μg g⁻¹ dry weight, probably due to genetic instability of the vector. This work highlights the advantages of using hairy roots for in vitro propagation of TMV compared with shooty teratomas and suspended plant cells, and demonstrates that batch root culture is more effective than semi-continuous operations for accumulation of high virus concentrations in the biomass.     

Further pharmacological evidence of the neuroprotective effect of catalpol from Rehmannia glutinosa

We have previously evaluated the neuroprotective effect of catalpol on aging mice induced by d-galactose, in which catalpol treatment ameliorated cognition deficits and attenuated oxidative damage in mice brain. To thoroughly elucidate the anti-aging effects of catalpol, the liver and spleen antioxidative systems and energy metabolism in senescent mice induced by d-galactose have been studied. Except control group, mice were subcutaneously injected with d-galactose (150 mg kg⁻¹ body weight) for 6 weeks. Meanwhile, drug group mice were treated with catalpol (2.5, 5, 10 mg kg⁻¹ body weight) and piracetam (300 mg kg⁻¹ body weight) for the last 2 weeks. The activities of endogenous antioxidants and the level of glutathione (GSH) and lipid peroxide in the liver and spleen were assayed. Compared to control group, model group mice had significantly lower spleen index (spleen weight/body weight), lower level of GSH, lower activities of superoxide dismutase (SOD) and glutathione peroxidase (GSH-PX), higher level of malondialdehyde (MDA) in the liver and spleen. However, catalpol administration markedly reversed these effects of senescence induced by d-galactose. Simultaneously, catalpol noticeably elevated the decreased activities of lactate dehydrogenase (LDH), glutamine synthetase (GS), Na⁺-K⁺-ATPase, Ca²⁺-Mg²⁺-ATPase and decreased the elevated activity of creatine kinase (CK) in mice liver or spleen. These results implied that the anti-aging effects of catalpol were achieved at least partly by promoting endogenous antioxidant enzyme activities and normalizing energy disturbance. Catalpol may be a potential anti-aging agent and worth testing for further preclinical study aimed for senescence or neurodegenerative diseases such as Alzheimer's and Parkinson's diseases.     

Root phosphate exudation and pH shift in the rhizosphere are not responsible for aluminum resistance in rice

A series of hydroponic experiments and an agar culture experiment were carried out to investigate aluminum (Al) accumulation and translocation in two rice (Oryza sativa L.) cultivars (Kasalath and Koshihikari) that differ in Al resistance. Al-resistance mechanisms, including Pi exudation under Al stress and pH shifts in the rhizosphere, were also studied. Al content in rice shoots was 41 mg kg⁻¹ on average and did not differ between the two cultivars, which demonstrated that the rice cultivars were not Al accumulators. The majority of Al (95–97%) accumulated in roots. Al content in roots in the resistant cultivar (Koshihikari) was lower than that in the sensitive cultivar (Kasalath), which indicated that Al-exclusion mechanisms were mainly acting in rice. However, the rate of Pi exudation from the whole root or root tips was very low in both cultivars and was not significantly influenced by Al exposure, and thus seemed not to be the main Al-resistance mechanism. On the other hand, experiments with pH-buffered solution and color changes following culture in agar medium containing bromocresol purple revealed that the Al-induced pH increase could not explain the high Al resistance of rice. In addition, the Al content in shoots of Koshihikari was lower after the formation of iron plaque on the root surface, whereas that of Kasalath was not lower. These results suggested that rice roots cell wall components or root surfaces such as iron plaque, rather than pH changes and/or root exudates including organic acids and phosphate, play important roles in Al resistance in rice.     

Characterization of two quaternary ammonium chloride-resistant bacteria isolated from papermaking processing water and the biocidal effect on their biofilm formation

Biofilm formation and growth on equipment surfaces is detrimental to papermaking processes. However, a fundamental understanding leading to an optimal control strategy is yet to be found. Quaternary ammonium compounds (QAC) are being increasingly applied in the papermaking processes. Among them, the most frequently applied, N-alkyl-benzyl-dimethyl ammonium chloride, was employed in this study. To foster fundamental understanding of QAC efficacy towards biofilm control, two of the highest QAC-resistant strains of bacteria were isolated from the papermaking processing water and employed as model organisms. By the 16S rRNA gene sequencing technique, two Gram-negative rods with QAC resistance were identified as Morganella morganii (HB22) and the biofilm-forming Pseudomonas putida (HB45). The minimal inhibition concentration (MIC) values were 8 mg L⁻¹ for HB22 and 16 mg L⁻¹ for HB45, respectively, against QAC in basal medium (BM). However, both strains could grow under more than 150 mg L⁻¹ QAC in basal medium at neutral pH. As observed by crystal violet assay and fluorescent confocal microscopy, HB45 formed biofilm more slowly on stainless steel coupon which is the prime material of papermachine than on the surface of polystyrene, the most common material for food packaging and semi-finished/finished products. HB45 formed biofilm more slowly on stainless steel coupons than on polystyrene Petri dish surfaces, as observed by crystal violet assay and fluorescent confocal microscopy. For HB45, there was a marginal increase of inhibition of biofilm formation by increasing QAC concentration from 50 to 75 mg L⁻¹. By comparison of inhibition concentration in liquid state and in biofilm formation, the results implicate that the current practice in papermaking processes of adding biocide to qualitatively control planktonic bacterial communities does not ensure control of biofilm formation.