Solid phase microextraction/gas chromatography of Salmonella-infected beef

Eight strains of Salmonellae were incubated in TSB culture medium at 37 degrees C for 24 h. Volatile compounds derived from the bacteria were collected using solid-phase microextraction fibers and then applied to gas chromatography (GC). Similarity analysis of the GC patterns thus obtained could separate these strains on principal component similarity (PCS) scattergrams. Five major food-related pathogenic bacteria and 10 other bacteria (including one Salmonella strain) were also classified by growing in the same medium. It is then proposed to utilize this approach to improve the GC/PCS method of Nakai et al. [Nakai, S.; Wang, Z. H.; Dou, J.; Nakamura, S.; Ogawa, M.; Nakai, E.; Vangerstoep, J. J. Agric. Food Chem. 1999, 47, 576-583] that has been developed for screening safe foods by detecting bacteria contaminated foods. Inoculating food samples pre-enriched through preliminary incubation into a culture medium and then subjecting to the GC/PCS method after secondary incubation enhances the detectability of pathogenic bacteria.     

The effect of vesicular-arbuscular mycorrhizal inoculation on nutrient uptake and yield of alley-cropped cassava in a degraded Alfisol of southwestern Nigeria

Leaf and root (tuber) nutrient uptake patterns of cassava (Manihot esculenta Crantz) alley-cropped with gliricidia (Gliricidia sepium), leucaena (Leucaena leucocephala), and senna [(Senna (syn. Cassia) siamea] as influenced by vesicular-arbuscular mycorrhizal (VAM) inoculation in a degraded Alfisol were investigated in consecutive years. The cassava plants were mulched with fresh prunings of each hedgerow tree species at 2-month intervals in the second and third years of alley cropping. While VAM inoculation significantly influenced the root uptake of nutrients, the leaf uptake was not affected except for the uptake of P. In most cases, there was no difference in the nutrient concentration between inoculated and uninoculated plants, either in the leaf or in the root, indicating that the productivity of cassava was regulated by the amount of nutrients the roots could absorb. In spite of similar total soil N in all inoculated and uninoculated alley-cropped cassava plots and similar exchange-able soil K contents in inoculated and uninoculated alley-cropped cassava plots with leucaena and senna, greater uptake of N, P, and K and greater concentrations of K were observed in roots of inoculated alley-cropped cassava with gliricidia and leucaena than with senna. These results indicated that greater mineralization and availability of nutrients to cassava roots from prunings of nodulating gliricidia and leucaena than from non-nodulating senna may be important, particularly with efficient VAM inoculation, in these alley-cropping systems. Also, for similar nutrients in the inoculated and uninoculated cassava soils alley-cropped with each hedgerow species, VAM inoculation significantly enhanced cassava root dry weights, indicating that an effective VAM fungus can be an agent of greater nutrient uptake in a competitive environment.     

Soil Fertility Improvement by Litter Decomposition and Inoculation with the Fungus Mortierella sp. in Avocado Plantations of Colombia

Litter decomposition is a major process in nutrient recycling, despite that few studies have considered this in soil fertility management. The aim of this study was to evaluate the effect of litter decomposition and its inoculation with the fungus Mortierella sp. on soil fertility parameters in Andisols cultivated with avocado cv. Hass. Litterbags containing avocado leaves either uninoculated or inoculated were distributed around the trees. As control litter was not allowed to accumulate on the soil surface. Eighteen months later soil samples were collected just below uninoculated and inoculated litterbags and control sites. Soil pH, potassium, calcium, phosphorus, magnesium, and boron significantly increased with litter and in some sites the increase was higher with inoculation. By contrast, soil aluminum, iron, and manganese were significantly lower in the presence of litter (uninoculated and inoculated), whereas zinc was significantly higher when litter was present.     

A modified chemical procedure for rapid determination of glucosamine and its application for estimation of mold growth in peanut kernels and koji.

One-step hydrolysis of chitin to release glucosamine for quantitation was achieved by combining a chitin-containing sample (10-200 mg of sample size) in a test tube with 1 mL of 10 M HCl followed by vacuum treatment for 10 min, incubation at 28 degrees C for 30 min, replenishment with 3 mL of deionized water, nitrogen flushing, screw capping, and heat treatment at 140 degrees C for 60 min. A phosphate buffer solution (pH 12.5, 0.2 M) was effective in pH stabilization and enhancing colorimetric determination of glucosamine content. When the modified procedure was applied to analyze glucosamine content in the mycelia of various molds, glucosamine content varied mainly depending on mold species. In estimations of mold growth of the uninoculated peanut kernels incubated under a humidified condition for 5 weeks, cooked rice and soybean inoculated with conidia of Aspergillus oryzae for koji preparation, logarithms of the internal mold populations and glucosamine contents both increased with increases of incubation time. The modified procedure provided a rapid and reliable estimation of mold growth in various substrates.     

Rhizobium and phosphorus influence on lentil seed protein and lipid

Root nodulation by rhizobial bacteria and P fertilization may affect seed protein and lipid composition in plants by altering nitrogen (N) and phosphorus (P) nutrition or by eliciting metabolic responses by the host plant. This study was conducted to determine the effects of rhizobium and P fertilization on seed protein and lipid contents and yield of lentil (Lens culinaris Medik). Lentil was grown to maturity in a greenhouse with P levels of 0 (low) and 50 (high) mg kg^‐1 soil with or without inoculation with Rhizobium bacteria. At the low level of P, protein and lipid concentrations and protein contents were significantly higher in inoculated than in uninoculated plants. Seed dry weight and protein concentrations and contents were higher in inoculated than in uninoculated plants at the high level of P. Seed protein/lipid (Pro/L) concentration ratios varied between inoculated and uninoculated plants at both P levels, and was related to the intensity of root nodulation. Lipid and protein contents were highly correlated with P content in lentil seeds. Seed lipid and protein contents were lower at the high level of P in uninoculated than inoculated plants. The data indicate different patterns of seed P accumulation and different relationships between seed P content and protein and lipid contents in inoculated and uninoculated plants. This might indicate that the intensity of nodulation altered the response of seed protein and lipid metabolism to increasing P availability, which affected protein and lipid ratios.     

The role of arbuscular mycorrhizal fungi and cattle manure in the establishment of Tocoyena selloana Schum. in mined dune areas

In mined dune areas, revegetation with manured seedlings of native species is a common practice. Establishment of mycorrhized Tocoyena selloana seedlings in the mined coastal sand dunes of Northeast Brazil was tested. In greenhouse, seedlings were grown in substrates with 0, 5, 10, 15 or 20% cattle manure proportions and inoculated with Acaulospora longula, a mixture of native arbuscular mycorrhizal fungi (AMF) or uninoculated. The seedlings responded positively to the inoculation, but growth was limited in the absence of manure, independently of inoculation, and was higher with fertilizing doses ≥10%. The seedlings transplanted to the field were grown in a substrate with 16.5% manure and inoculated with A. longula or Gigaspora albida. After 13 months, 19 AMF species were identified in the rhizosphere and the inoculated plants were more colonized than those uninoculated. Plants associated to G. albida were taller and those associated to A. longula had a tendency of higher biomass than the uninoculated ones. Even though this tendency was not statistically significant, considering the effect on height and the low cost of inoculation it may be a feasible practice to maximize environment restoration.     

Colonization and growth promotion characteristics of Enterobacter sp. and Herbaspirillum sp. on Brassica oleracea

We investigated the effects of inoculating a dicot plant, Brassica oleracea , with nitrogen-fixing endophytic bacteria isolated from monocots. The bacteria used were Enterobacter sp. strain 35 isolated from sugarcane and Herbaspirillum sp. strain B501 isolated from wild rice. Under glasshouse conditions, B. oleracea inoculated with strain 35 had a significantly greater fresh weight than uninoculated plants, and the fresh weight of plants inoculated with strain B501 tended to be higher than that of uninoculated plants. We conducted a laboratory-scale experiment to confirm the above results and to investigate the colonization and nitrogen-fixing abilities of these bacteria. Plants inoculated with Enterobacter sp. strain 35-1, a green fluorescent protein (GFP)-labeled strain derived from strain 35, had larger bacterial populations and greater acetylene reduction activity than those inoculated with Herbaspirillum sp. strain B501 gfp 1. Strain 35-1 colonized the intercellular spaces and the junctions of the lateral roots with the parent root. The results indicated that isolates from monocots can successfully colonize B. oleracea (a dicot) and promote plant growth.     

A method for identification and mapping potentially acid sulfate soils in Jutland, Denmark

A method for mapping potentially acid sulfate soils in Jutland, Denmark is described. First the wetlands were outlined, using already existing topographic maps. Then 7900 profiles, evenly distributed over the wetland areas, were examined to point out areas with potentially acid sulfate soils. The method used to identify potentially acid sulfate material was, for carbonate-free samples, a pH-measuring at the sampling time and after the samples were inoculated with soil water extract from an acid sulfate soil and 2, 8 or 16 weeks of incubation. For carbonate-containing samples the pyrite content was compared to the acid-neutralizing capacity. A map was constructed showing the ratio of profiles containing potentially acid sulfate soil samples to total number of profiles examined within natural geographical wetland regions.The investigation showed that 35% of the wetlands in Jutland have a high frequency of potentially acid sulfate soils.     

Effects of indigenous and introduced arbuscular mycorrhizal fungi on the growth of Allium fistulosum under field conditions

ABSTRACT

Enhanced phosphorus (P) uptake from the soil and increased plant growth related to arbuscular mycorrhizal (AM) fungi in pot culture, using sterilized soil, are well-known phenomena. However, these enhancements are not widely observed under field conditions because field sterilization is difficult. The aim of this study was to investigate the effects of AM fungi on P uptake and the growth of Allium fistulosum in non-fumigated and fumigated fields, under different levels of P availability. Plants were inoculated with the AM fungus Glomus R-10 and grown in fumigated soil. For the uninoculated treatment, a sterilized inoculum was applied directly. The field was fumigated using dazomet. Superphosphate was applied to the field at the rates of 0 (P0) or 500 (P500) kg P₂O₅ ha^?1. The inoculated and uninoculated plants were transplanted into the fields and sampled three times to measure AM fungal colonization, shoot P concentration, and shoot dry weight of the plants. At the transplanting stage, AM fungal colonization was observed in the inoculated plants (>70%) but not in the uninoculated plants. At the third sampling, irrespective of P treatment, AM fungal colonization was observed both in the uninoculated and inoculated plants in the non-fumigated field, and there was no difference in shoot P content and shoot dry weight between the inoculated and uninoculated plants. AM fungal colonization in the fumigated field was higher in the inoculated than uninoculated plants, irrespective of P treatment; shoot P content and shoot dry weight were both higher in the inoculated plants than in the uninoculated plants with P0. These results suggest that the responses of A. fistulosum to AM fungal inoculation under the low-P and fumigated conditions are similar to those observed in sterilized pot culture conditions.     

Most probable number method for isolation and enumeration of Staphylococcus aureus in foods: collaborative study

Enumeration of Staphylococcus aureus in foods was collaboratively studied by comparing the present AOAC final action method, 46.062, which uses trypticase soy broth with 10% NaCl to a proposed replacement method which uses the same broth with 1% sodium pyruvate added. Fifteen collaborators analyzed uninoculated samples of milk, tuna salad, and ground turkey, as well as samples inoculated with low (10(2) cells/g), middle (10(4) cells/g), and high (10(6) cells/g) levels of S. aureus. The samples were frozen immediately to maintain the inoculated level of S. aureus in the food. A different strain of S. aureus was used for each food; heat-stressed S. aureus cells were used to inoculate the milk samples. The pyruvate-amended broth significantly (alpha = 0.05) increased enumeration of low, middle, and high levels of S. aureus from milk and ground turkey, and from tuna salad at middle and high levels. The pyruvate-amended media method has been adopted official first action to replace method 46.062.     

Gas chromatographic detection of D-(-)-2,3-butanediol and butyric acid produced by sporeformers in cream-style corn and canned beef noodle soup: collaborative study

A gas chromatographic method that identifies sporeformers as the cause of spoilage in swollen cans of low-acid foods was collaboratively studied in 2 stages. Two organic compounds produced by sporeformers, D-(-)-2,3-butanediol and butyric acid, are measured in the upper phase after centrifugation of the liquid portion of the can contents. Each sample is assayed on 2 packed columns designed for the assay of aqueous solutions of volatile fatty acids, using flame ionization detectors. For study 1, 16 duplicate inoculated cans of cream-style corn and beef noodle soup were sent to 9 collaborators. For study 2, 7 collaborators received 11 duplicate inoculated cans of the 2 foods. Duplicate uninoculated cans of each food served as negative controls. The inocula were 6 sporeforming organisms (4 Clostridium and 2 gas-forming Bacillus species) and 2 nonsporeformers. After the deletion of marginal samples, the percentages of correctly identified sporeformers and nonsporeformers in beef noodle soup were 83 (110/132) and 90 (54/60), respectively; corresponding percentages for cream-style corn were 80 (98/123) and 100 (35/35). The method has been adopted official first action.     

Degradation of the fungicide metalaxyl and its non-extractable residue formation in soil clay and silt fractions

The proportion of organic matter and mineral composition are important factors determining the formation and type of non-extractable residues (NERs) of pesticides in soil. In this study, we investigated the enantioselectivity in degradation and NER formation of the chiral fungicide metalaxyl in soil particle size fractions (silt and clay). Microbial and extracellular enzyme activities during these processes were monitored in incubation of silt and clay samples isolated from sterilized and non-sterilized soil samples collected from a long-term agricultural field experimental site in Ultuna, Sweden. The temporal influence on the fate of the fungicide was noted by short-term (10-d) and long-term (92-d) incubations. Besides the acquisition of quantitative data with gas chromatography-mass spectrometry (GC/MS), stereoselective analyses were performed with chiral GC/MS. Quantitative results pointed to a higher metabolism rate of the pesticide through microbial activity than through extracellular enzyme activity. This was also confirmed by the enantioselective depletion of R-metalaxyl and the subsequent formation of R-metalaxyl acid in microbially active samples from non-sterilized soil. The silt fraction containing a high amount of organic matter exhibited a significant hydrolyzable proportion of metalaxyl NERs that was releasable under alkaline conditions. On the contrary, the clay fraction showed an enhanced affinity for covalently bound residues. Based on our results, we recommend differentiating between reversibly and irreversibly bound proportions of pesticides in persistence and environmental risk assessment because the reversible fraction contained potentially bioavailable amounts of residues that may be released under natural conditions.     

丛枝菌根对酸枣实生苗耐盐性的影响

本文研究了在土中加入不同量NaCl条件下 (0、1 5、3 0、4 5gkg-1干土 )接种丛枝菌根真菌 (AMF)Glomusmosseae对盆栽酸枣 (ZizyphusspinosusHu)实生苗生长及耐盐性的影响。结果表明 ,无论接种与否 ,植株的高度、根茎叶的干鲜重均随土壤NaCl浓度的增加而降低 ,而根、茎、叶和整株的Na浓度及Na全量均随土壤NaCl浓度的增加而增大。在土壤盐浓度相同的条件下 ,接种AMF植株的生长量 (株高、鲜重、干重等 )和叶片的叶绿素含量显著高于不接种植株。接种AMF的植株茎、叶中Na浓度低于不接种植株 ,而根中Na浓度、植株Na总量显著高于不接种植株。盐浓度最大的接种处理 ,其植株生长量和叶片叶绿素含量均高于不加盐不接菌处理。播种时进行盐胁迫处理和播种后 4 0d开始进行盐胁迫处理对菌根的侵染率、植株生长的影响差异不显著。上述四种盐浓度播种时进行盐处理的接种AMF植株的总干重比不接种植株分别提高 16 4 %、14 9%、4 8%、35 % ,在播种后 4 0d进行盐处理的接种AMF的植株比不接种植株分别提高 194 %、12 7%、72 %、4 6 %。结果证明 ,酸枣实生苗具有较强的耐盐性 ,其生长对菌根真菌有很强的依赖性 ,接种菌根真菌提高了其耐盐能力。     

Use of mycorrhizal seedlings on recovery of mined dunes in northeastern Brazil

The exploitation of minerals from coastal dunes in northeastern Brazil requires subsequent revegetation for ecosystem recovery. In mined dunes areas, we have compared the growth of Guazuma ulmifolia and Tabebuia roseo-alba seedlings using substrates containing 10 or 15% of cattle manure, uninoculated or inoculated with a mixture of native arbuscular mycorrhizal fungi (AMF) or exotic AMF (Acaulospora longula). The inoculated plants had a higher percentage of colonization than those that were uninoculated. Plants of G. ulmifolia had the highest growth when inoculated with native AMF and fertilized with 10% manure or inoculated with A. longula and fertilized with 15% manure. In general, fertilization with 15% manure did not produce greater seedling development and had a negative effect on the effectiveness of the symbiosis. Twenty one AMF species were recorded in the planting areas at the end of the experiments, with a predominance of species that form acaulosporoid spores in areas with T. roseo-alba and gigasporoid spores in areas with G. ulmifolia plants. The incorporation of 10% cattle manure and native AMF in the substrate of T. roseo-alba and G. ulmifolia seedlings contributes to the initial establishment of plants in the field and to the incorporation of AMF propagules in the soil of the revegetated mined dunes.     

两株细菌与丛枝菌根真菌联合接种对红壤中DEHP降解的影响

采用绿豆为供试植物,通过温室盆栽试验研究接种邻苯二甲酸二(2-乙基己基)酯(DEHP)降解菌与丛枝菌根(Arbuscular mycorrhiza,AM)真菌对DEHP污染土壤的修复作用以及对植物生长的影响。试验土壤中添加DEHP浓度为100mg kg-1,试验设AM真菌Acaulospora 90034、降解菌Bacillus sp.DW1和Gordonasp.DH3单独接种以及互相组合的联合接种处理,同时设置不接种的对照处理(CK)。苗后60d收获植株。结果表明,AM真菌能很好地侵染绿豆的根系。菌根侵染提高了绿豆植株的干重,同时也促进了绿豆的磷营养,但接种DW1与DH3对菌根侵染率与绿豆生长都没有显著影响。三种菌剂无论是单独或者联合接种都能显著促进土壤中DEHP的降解,但三种菌剂同时接种对DEHP的降解能起到最好的协同作用。同时,接种AM真菌也减少了DEHP在绿豆地上部分的累积,这些都为DEHP污染农田土壤的生物修复提供了理论依据。     

长期施肥黑土微生物区系及功能多样性的变化

Black soil （Mollisol） is one of the main soil types in northeastern China. Biolog and polymerase chain reactiondenaturing gradient gel electrophoresis （PCR-DGGE） methods were used to examine the influence of various fertilizer combinations on the structure and function of the bacterial community in a black soil collected from Harbin, Heilongjiang Province. Biolog results showed that substrate richness and catabolic diversity of the soil bacterial community were the greatest in the chemical fertilizer and chemical fertilizer＋manure treatments. The metabolic ability of the bacterial community in the manure treatment was similar to the control. DGGE fingerprinting indicated similarity in the distribution of most 16S rDNA bands among all treatments, suggesting that microorganisms with those bands were stable and not influenced by fertilization. However, chemical fertilizer increased the diversity of soil bacterial community. Principal com- ponent analysis of Biolog and DGGE data revealed that the structure and function of the bacterial community were similar in the control and manure treatments, suggesting that the application of manure increased the soil microbial population, but had no effect on the bacterial community structure. Catabolic function was similar in the chemical fertilizer and chemical fertilizer＋manure treatments, but the composition structure of the soil microbes differed between them. The use of chemical fertilizers could result in a decline in the catabolic activity of fast-growing or eutrophic bacteria.     

Comparative studies of nucleic acid hybridization assay for Listeria in foods

A nucleic acid hybridization assay has been developed for Listeria spp. in dairy foods and environmental samples. The assay is based on detection of unique Listeria 16S rRNA sequences by using a 32P-labeled synthetic DNA probe. Inclusivity and exclusivity of the probe were confirmed with 139 Listeria isolates representing all known species, and 73 non-Listeria bacterial strains. In this paper, we present results from our preliminary studies comparing the hybridization assay with conventional culture on a total of 575 specimens that represent a variety of inoculated and uninoculated foods and environmental samples. The assay, which is done in a filter manifold format after 2 days of cultural enrichment, requires a total assay time of less than 2.5 days. The false-negative rate for all sample groups tested using the GENE-TRAK hybridization assay was less than the rate for culture. Thus, the new assay allows rapid screening of the indicated product groups and provides reliable numerical results.     

砷污染土壤中接种丛枝菌根真菌和蚯蚓对土壤线虫群落和植物砷吸收的影响

The influences of arbuscular mycorrhizal fungi (MF, Acaulospora spp. and Glomus spp.), rice straw and earthworms (RE, Eisenia foetida) on nematode communities and arsenic (As) uptake by maize (Zea mays L.) in As-contaminated soils were examined in a field experiment conducted in Wujiang, Jiangsu Province, China. The experiment was designed as a 2 × 2 factorial with the factors of MF (inoculated or uninoculated) and RE (added or not added). The results demonstrated that MF inoculation led to significantly higher root colonization of MF and root dry weight. Plants inoculated with both MF and RE had the highest As concentrations in root. The number of total nematodes increased with MF inoculation when RE was absent, and decreased with RE addition when MF was inoculated. The improved abundance of nematodes with the MF treatment implied that the tested MF acted as food sources for fungivores. The abundances of omnivores-predators and plant parasites were reduced by earthworm activity. Twenty-seven genera of nematodes were identified, with Filenchus dominant in all treatments. Trophic diversity (TD), Shannon-Weaver diversity (H′), Simpson dominance index (λ), and species richness (SR) indicated higher species diversity, more proportionate species composition, evenly distributed species, and more food sources in the MF, RE, and their interaction treatments. Maturity index (MI) showed a moderately disturbed environment due to As pollution. Besides enhancing plant uptake of contaminants, MF and RE amendments could also improve soil health by restoring the structure of soil communities, as reflected by more stable nematode community structure.     

Comparative study of colorimetric DNA hybridization method and conventional culture procedure for detection of Salmonella in foods

A second generation nucleic acid hybridization assay has been developed and evaluated against the conventional culture method for detection of salmonellae in foods. The assay involves a liquid hybridization with Salmonella-specific oligonucleotide probes, capture of probe:target hybrids onto a solid support (plastic dipstick), and a colorimetric end point detection. The assay can be completed in 2.5 h, following approximately 44 h of culture enrichment. One thousand samples representing 20 food types were analyzed in parallel by both methods. Samples included uninoculated test product, and product inoculated with Salmonella at 2 levels. Eighteen Salmonella serotypes were used as inocula. The data demonstrate that the colorimetric hybridization method and the conventional culture method are equivalent in their ability to detect Salmonella contamination of foods.     

Changes in the vesicular‐arbuscular mycorrhizal dependency of Albizia ferruginea and Enterolobium cyclocarpum in response to soil phosphorus concentration 1

A greenhouse experiment was conducted to determine the degree to which Albizia ferruginea and Enterolobium cyclocarpum respond to colonization of their roots by the vesicular‐arbuscular mycorrhizal fungus (VAMF) Glomus aggregatum. Plants were grown in pots containing a subsurface ultisol uninoculated or inoculated with the fungus at three target soil solution phosphorus (P) concentrations. VAMF inoculation enhanced pinnule P content of Albizia but not of Enterolobium at the native P concentration of the experimental soil. However, dry matter yield was not affected by VAMF inoculation for either species. Mycorrhizal inoculation effect was either negative or nil at the highest soil solution P concentration tested. The highest mycorrhizal inoculation effect was observed at soil P concentration of 0.02 mg/L. Based on these data, both Albizia and Enterolobium were classified as highly mycorrhizal dependent species.