Wheat and soil bromide dynamics after fumigation with methyl bromide in a mediterranean climate

Summary Soil and wheat bromide dynamics are studied in methyl bromide-fumigated plots in a Mediterranean climate. Bromide residues range between 5 to 10 ppm in the fumigated soil and they are distributed to a depth of 50–60 cm, where a compacted layer exists, in accordance with soil organic matter and moisture distribution. The total amount of bromide in soil is 5.8 gm⁻² up to a depth of 1 m and it remains almost constant during the wheat growth period. The plant bromide concentration decreases throughout the development of spring wheat. The bromide distribution in the different plant organs was identical in the two years studied and it is correlated with the chloride content. Fumigation increases the phosphorus concentration in wheat and does not affect sulphur and chloride. Though the bromide concentration in the fumigated soils is high, the levels in the plants growing in it do not cause scorched areas. This may be due to antagonic Br/Cl and Br/NO₃ effects.     

甲基溴土壤消毒替代技术条件下的线虫生态学研究

为评价和筛选几种甲基溴替代技术及其对土壤线虫群落的影响 ,2 0 0 1年 6月～ 2 0 0 2年 3月对 5种土壤消毒处理的线虫数量和群落结构及微生物量动态作了测定和分析。试验共分离到土壤线虫 4个目 14个科属 ,包括小杆目 (Rhabditida)、垫刃目(Tylenchida)、矛线目 (Dorylaimida)、单宫目 (Monhysterida)。小杆目线虫占总数的 88.7% ,表明食细菌的小杆目线虫是该温室土壤线虫群落的优势类群。分析表明甲基溴 VIF、威百亩、威百亩 VIF三种措施的消毒效果达到了甲基溴处理的水平 ,可作为甲基溴土壤消毒替代技术 ,而太阳能 BCA处理未达到甲基溴消毒的效果。研究显示同一处理的线虫数量在两个番茄品种(AF179和毛粉 80 2 )间不存在显著差异 ,即表明这两种番茄品种不是影响土壤线虫数量动态的主要因素。对消毒处理后土壤线虫各营养类群在群落中的比例进行分析 ,发现与对照相比 ,化学消毒提高了线虫群落中优势类群 (即食细菌线虫 )的比例 ,而使弱势类群的比例下降 ,这表明土壤线虫的弱势类群对化学熏蒸剂更加敏感。两番茄品种小区中土壤食细菌、食真菌线虫数量与微生物量碳之间呈显著正相关关系 ,表明微生物生物量的消长受土壤消毒措施的影响 ,同时也证实了上述两营养类群线虫与土壤微生物间的食物依赖关系。     

Soil fumigation with methyl bromide: the uptake and distribution of inorganic bromide in tomato plants

Tomato plants grown in soil previously fumigated with methyl bromide accumulated inorganic bromide in the foliage. The concentration present depended on the rate of application of methyl bromide to the soil and on the interval between, soil fumigation and planting, two factors determining the concentration in the soil of inorganic bromide arising from the breakdown of the fumigant. The concentration of bromide in the leaves decreased from the base to the tip of the plant, and increased with the age of the tissue. Bromide was accumulated in the fruit, but to a lesser extent than in the leaves. Mature fruit from plants grown in soil fumigated at the commercially applied rate of 1.5 lb/100 ft² (73 g/m²) contained at the most 45 μg/g of fresh tissue, and generally not more than half this value. The concentration of bromide in fruit was related to the concentration of inorganic bromide present in the soil, but not to the state of ripeness or the position of the fruit on the plant. Similar results were obtained for leaves and fruit from plants grown in soil supplemented with inorganic bromide.     

溴甲烷熏蒸对土壤反硝化作用及nosZ型反硝化微生物群落结构的影响

【目的】探究溴甲烷熏蒸对土壤反硝化作用的影响及机制。【方法】本研究采用nos Z-PCR-RFLP(Restriction fragment length polymorphism)方法、nos Z-MPN-PCR(Most-Probable-Number-PCR)计数法和土壤硝酸根的消灭率方法研究溴甲烷熏蒸对土壤nos Z型反硝化细菌群落结构、数量及反硝化活性的影响。【结果】实验结果说明溴甲烷熏蒸剂熏蒸土壤100 d土壤的反硝化作用与对照无显著差异(P>0.05)。溴甲烷熏蒸土壤和对照土样nos Z型反硝化细菌群落的Margalef指数,Shannon-Wiener和Evenness指数无显著差异(P>0.05)。溴甲烷熏蒸土壤和对照土壤中存在Uncultured bacterium partial rhodopsendomonas、pseudomonas fluorescens、Herbacspirillum、Mesorhizobium和Bradyrhizobium,并且此6种微生物均是试验土样和对照土样的优势种群;对照土壤中检测到Azospirillum、Rhizobium melibei和Nitrosospira multiformis,在溴甲烷熏蒸土壤中未检测到;而溴甲烷熏蒸土壤中检测到Uncultured Azospirillum,Mesorhizobium在对照土壤中未检测到。通过nos Z-MPN-PCR计数法得出反硝化细菌数量比对照低1.4倍。【结论】说明溴甲烷熏蒸100d土壤的nos Z型反硝化微生物群落组成和反硝化细菌数量发生变化,而土壤的反硝化作用与对照无显著差异。     

Allelopathy in a broad spectrum of environments as illustrated by bracken

Bracken is a weed that strongly dominates a wide variety of vegetation types throughout the world. The primary mechanism of interference that this fern brings to bear upon associated plants that allows it to establish and maintain dominance is allelopathy. But due to the nature of the interaction between allelopathy and the environment, bracken has evolved a mechanism of toxin release which allows the fern to exert its dominance most effectively in each particular habitat in which it grows. In southern California, toxin release is timed for the initiation of the wet season and thus the initiation of germination of associated plants. Toxins come primarily from the dead, standing fronds. In the Pacific Northwest, toxin release is timed for the breaking of dormancy in spring after the snow melts and soil temperature rises. Toxins come primarily from bracken litter, roots and rhizomes. In tropical Costa Rica, toxin release takes place all year round, timed for the continual growth of associated plants. Toxins come primarily from a continual production by the green fronds. The interrelationship between allelopathy and the environmental complex is discussed.     

Degradation of 1,3-dichloropropene by a soil bacterial consortium and Rhodococcus sp. AS2C isolated from the consortium

A bacterial consortium capable of degrading the fumigant 1,3-D ((Z)- and (E)-1,3-dichloropropene) was enriched from an enhanced soil. This mixedculture degraded (Z)- and (E)-1,3-D only in the presence of a suitable biodegradable organic substrate, such as tryptone, tryptophan, or alanine. After 8 months of subculturing at 2- to 3-week intervals, a strain of Rhodococcus sp. (AS2C) that was capable of degrading 1,3-D cometabolically in the presenceof a suitable second substrate was isolated. (Z)-3-chloroallyl alcohol (3-CAA) and (Z)-3-chloroacrylic acid (3-CAAC), and (E)-3-CAA and (E)-3-CAAC were the metabolites of (Z)- and (E)-1,3-D, respectively. (E)-1,3-D was degraded faster than (Z)-1,3-D by the strain AS2C and the consortium. AS2C also degraded (E)-3-CAA faster than (Z)-3-CAA. Isomerization of (E)-1,3-D to (Z)-1,3-D orthe (Z) form to the (E) form did not occur.     

Description of toluene inhibition of methyl bromide biodegradation in seawater and isolation of a marine toluene oxidizer that degrades methyl bromide

Methyl bromide (CH3Br) and methyl chloride (CH3Cl) are important precursors for destruction of stratospheric ozone, and oceanic uptake is an important component of the biogeochemical cycle of these methyl halides. In an effort to identify and characterize the organisms mediating halocarbon biodegradation, we surveyed the effect of potential cometabolic substrates on CH3Br biodegradation using a 13CH3Br incubation technique. Toluene (160 to 200 nM) clearly inhibited CH3Br and CH3Cl degradation in seawater samples from the North Atlantic, North Pacific, and Southern Oceans. Furthermore, a marine bacterium able to co-oxidize CH3Br while growing on toluene was isolated from subtropical Western Atlantic seawater. The bacterium, Oxy6, was also able to oxidize o-xylene and the xylene monooxygenase (XMO) pathway intermediate 3-methylcatechol. Patterns of substrate oxidation, lack of acetylene inhibition, and the inability of the toluene 4-monooxygenase (T4MO)-containing bacterium Pseudomonas mendocina KR1 to degrade CH3Br ruled out participation of the T4MO pathway in Oxy6. Oxy6 also oxidized a variety of toluene (TOL) pathway intermediates such as benzyl alcohol, benzylaldehyde, benzoate, and catechol, but the inability of Pseudomonas putida mt-2 to degrade CH3Br suggested that the TOL pathway might not be responsible for CH3Br biodegradation. Molecular phylogenetic analysis identified Oxy6 to be a member of the family Sphingomonadaceae related to species within the Porphyrobacter genus. Although some Sphingomonadaceae can degrade a variety of xenobiotic compounds, this appears to be the first report of CH3Br degradation for this class of organism. The widespread inhibitory effect of toluene on natural seawater samples and the metabolic capabilities of Oxy6 indicate a possible link between aromatic hydrocarbon utilization and the biogeochemical cycle of methyl halides.     

Microbial biomass of a grassland soil as estimated by the fumigation and direct counting methods

The total biomass of microorganisms estimated by means of the fumigation method in the root-free soil from a submontane grassland under variant management ranged from 40.8 to 60.7 mg C per 100 g, as compared with 69.4 to 143.0 mg C per 100 g for the rhizosphere soil. The biomass of bacteria and that of fungi calculated for the root-free soil from direct counts was 4.1 to 19.6 mg C per 100 g and 19.9 to 32.7 mg C per 100 g, respectively. A correlation (r=0.738) was found between results obtained by the two methods.     

Development of a combined cold storage and methyl bromide fumigation treatment to control the American serpentine leaf miner Liriomyza trifolii (Diptera:Agromyzidae) in imported chrysanthemum cuttings

Individual chrysanthemum cuttings and leaves infested with eggs and larvae of the alien leaf miner Liriomyza trifolii, and batches of pupae, were treated in the laboratory to find an effective quarantine treatment to control the pest in imported cuttings. The laboratory tests were based on a statutory quarantine treatment of 2 days' cold storage at 1–2°C followed by methyl bromide fumigation at 15°C with a concentration time product (CTP) of 54 g h/m³, which is used to control Spodoptera littoralis on imported chrysanthemum cuttings. Treatments of 2 days' storage at 1–2°C followed by methyl bromide fumigation at 15°C with a range of CTPs were used to obtain accurate dose-response lines and estimate the LD99 and LD99 9 for each stage of L. trifolii. The largest estimates of the LD99 for eggs, larvae and pupae up to 3 days old were 40·04, 34·49 and 42·64g h/m³ respectively. These results indicate that the Spodoptera treatment should give high levels of kill of most stages of L. trifolii. However, the LD99 values for pupae more than 3 days old were greater than those for eggs, larvae and young pupae. Therefore if this treatment were adopted as a quarantine measure against L. trifolii, good prophylactic treatments and rigorous pre-packing inspections in exporting countries would need to be maintained, to minimise any risk of importing pupae. It would also be necessary to ensure that the temperature of the imported cuttings was raised uniformly to 15°C after cold storage and prior to fumigation. The practicality of the technique as a commercial treatment will depend on whether it is possible to achieve this without causing unacceptable phytotoxicity.     

Aerobic biodegradation of 1,2-dichloroethane and 1,3-dichloropropene by bacteria isolated from a pulp mill wastewater effluent in South Africa

Large volumes of chlorinated aliphatic hydrocarbons are produced annually for a variety of industrial and commercial uses. They therefore constitute common contaminants of soil and groundwater causing serious environmental and human health problems. In this study, three bacteria were isolated from a pulp mill wastewater effluent in South Africa by culture enrichment technique and characterized for their ability to degrade 1,2-dichloroethane (1,2-DCE) and 1,3-dichloropropene (1,3-DCP). Specific growth rate constants of the organisms ranged between 0.864∼1.094 and 0.530∼0.585 d⁻¹ in 1.2-DCE and 1,3-DCP, respectively, while the degradation rate constant of the compounds ranged variously between 0.33 and 1.006 d⁻¹, with 1,2-DCE generally better utilized than 1,3-DCP. Gas chromatographic analysis revealed up to 75 and 80% removal of 1,2-DCE and 1,3-DCP, respectively, above that observed in the control bottles. These organisms also demonstrated high haloalkane dehalogenase activities with specific dehalogenase activities ranging between 0.25∼0.31 U (mg protein)⁻¹. Analysis of their 16S rRNA gene sequences revealed that they belong to the generaPaenibacillus, Bacillus, andMicrobacterium.     

Functional properties of the pOV13 plasmid as a vector for DNA cloning in a broad spectrum of gram negative bacteria

The birepliconed plasmid pOV13 possesses all the properties of a vector for DNA cloning in a broad host range of bacterial cells. pOV13 is transfered by transformation and stably inherited by Escherichia coli, Brucella, Pseudomonas cells determining the resistance to streptomycin, tetrocycline and kanamycin in these bacteria. The plasmid pOV13 is a multicopy plasmid optimal in replication capacity (23kb). The plasmid carries single sites for some restriction endonucleases that are used for DNA cloning, including some restriction sites in antibiotic resistance genes. The examples of DNA cloning with the selection of recombinant clones by the insertional inactivation of kanamycin or tetracycline resistance and expression of the cloned DNAs are presented.     

Repeated inoculation as a strategy for the remediation of low concentrations of phenanthrene in soil

Phenanthrene, a polycyclic aromatic hydrocarbon, becomes increasingly unavailable to microorganisms for degradation as it ages in soil. Consequently, many bioaugmentation efforts to remediate polycyclic aromatic hydrocarbons in soil have failed. We studied theeffect of repeatedly inoculating a soil with a phenanthrene-degrading Arthrobacter sp. on the mineralization kinetics of low concentrations of phenanthrene. After the first inoculation, the initial mineralization rate of 50 ng/g phenanthrene declined in a biphasicexponential pattern. By three hundred hours after inoculation, there was no difference in mineralization rates between the inoculated and uninoculated treatments even though a large fraction of the phenanthrene had not yet been mineralized. A second and third inoculation significantly increased the mineralization rate, suggesting that, though themineralization rate declined, phenanthrene remained bioavailable. Restirring the soil, without inoculation, did not produce similar increases in mineralization rates, suggesting absence of contact between cells and phenanthrene on a larger spatial scale (>mm) is not the cause of the mineralization decline. Bacteria inoculated into soil 280 hours beforethe phenanthrene was added could not maintain phenanthrene degradation activity. We suggest sorption lowered bioavailability of phenanthrene below an induction threshold concentration for metabolic activity of phenanthrene-degrading bacteria.     

Repurposing the FDA-approved anticancer agent ponatinib as a fluconazole potentiator by suppression of multidrug efflux and Pma1 expression in a broad spectrum of yeast species

Fungal infections have emerged as a major global threat to human health because of the increasing incidence and mortality rates every year. The emergence of drug resistance and limited arsenal of antifungal agents further aggravates the current situation resulting in a growing challenge in medical mycology. Here, we identified that ponatinib, an FDA-approved antitumour drug, significantly enhanced the activity of the azole fluconazole, the most widely used antifungal drug. Further detailed investigation of ponatinib revealed that its combination with fluconazole displayed broad-spectrum synergistic interactions against a variety of human fungal pathogens such as Candida albicans, Saccharomyces cerevisiae and Cryptococcus neoformans. Mechanistic insights into the mode of action unravelled that ponatinib reduced the efflux of fluconazole via Pdr5 and suppressed the expression of the proton pump, Pma1. Taken together, our study identifies ponatinib as a novel antifungal that enhances drug activity of fluconazole against diverse fungal pathogens.     

Intensity of nitrification in soil as a function of time and soil moisture

Proceeding from three previously derived expressions for the intensity of nitrification in soil as a function of time (logΣN=K.logt+q), as a function of incubation moisture (logΣN=A.pF _i+B), as a function of initial moisture (logΣN=C.pF _v+D), it was shown that the nitrification intensity as a function of time and of moisture can be expressed by the bilinear function log ΣN=a.pF _i.logT+b.pF _i+c.logt+d; as a function of time and of initial moisture by the bilinear function logΣ=N=a.pF _v.logt+b.pF _v+c.logt+d; as a function of initial and incubation moisture by the bilinear function log ΣN=a.pF _ipF _v+b.pF _i+c.pF _v+d. The intensity of nitrification as a function of time, incubation moisture and initial moisture may be expressed by the multilinear function log ΣN=a.pF _i.pF _v.logt+b.pF _i.pF _v+c.pF _i.logt+d.pF _v.logt+e .pF _i+f.pF _v=g.logt+h. This function is valid for all the incubation moistures lying between pF _i 3.0 and 4.0 and for all initial moistures between 3.5 and 5.9 provided that the incubation temperature remains constant.     

Influence of biochemical quality on C and N mineralisation from a broad variety of plant materials in soil

We studied C and N mineralisation patterns from a large number of plant materials (76 samples, covering 37 species and several plant parts), and quantified how these patterns related to biological origin and selected indicators of chemical composition. We determined C and N contents of whole plant material, in water soluble material and in fractions (neutral detergent soluble material, cellulose, hemicellulose and lignin) obtained by stepwise chemical digestion (modified van Soest method). Plant materials were incubated in a sandy soil under standardised conditions (15 °C, optimal water content, no N limitation) for 217days, and CO₂ evolution and soil mineral N contents were monitored regularly. The chemical composition of the plant materials was very diverse, as indicated by total N ranging from 2 to 59 mg N g^–1, (i.e. C/N-ratios between 7 and 227). Few materials were lignified (median lignin=4% of total C). A large proportion of plant N was found in the neutral detergent soluble (NDS) fraction (average 84%) but less of the plant C (average 46%). Over the entire incubation period, holocellulose C content was the single factor that best explained the variability of C mineralisation (r=–0.73 to –0.82). Overall, lignin C explained only a small proportion of the variability in C mineralisation (r=–0.44 to –0.51), but the higher the lignin content, the narrower the range of cumulative C mineralisation. Initial net N mineralisation rate was most closely correlated (r=0.76) to water soluble N content of the plant materials, but from Day 22, net N mineralisation was most closely correlated to total plant N and NDS-N contents (r varied between 0.90 and 0.94). The NDS-N content could thus be used to roughly categorise the net N mineralisation patterns into (i) sustained net N immobilisation for several months; (ii) initial net N immobilisation, followed by some re-mineralisation; and (iii) initially rapid and substantial net N mineralisation. Contrary to other studies, we did not find plant residue C/N or lignin/N-ratio to be closely correlated to decomposition and N mineralisation.