Temporal Changes in the Ectomycorrhizal Community in Two Soil Horizons of a Temperate Oak Forest

The species structure of an ectomycorrhizal (ECM) community was assessed monthly for 15 months in the two horizons (A1 and A2) of an oak temperate forest in northeastern France. Ectomycorrhizal species were identified each month by internal transcribed spacer sequencing. Seventy-five fungal symbionts were identified. The community was dominated by Tomentellaceae, Russulaceae, Cortinariaceae, and Boletales. Four species are abundant in the study site: Lactarius quietus, Tomentella sublilacina, Cenococcum geophilum, and Russula sp1. The relative abundance of each species varied depending on the soil horizon and over time. Some species, such as L. quietus, were present in the A1 and A2 horizons. C. geophilum was located particularly in the A2 horizon, whereas T. sublilacina was more abundant in A1. Some species, such as Clavulina sp., were detected in winter, while T. sublilacina and L. quietus were present all year long. Our results support the hypothesis that a rapid turnover of species composition of the ECM community occurs over the course of a month. The spatial and temporal unequal distribution of ECM species could be explained by their ecological preferences, driven by such factors as root longevity, competition for resources, and resistance to environmental variability.     

Fertilization alters nitrogen isotopes and concentrations in ectomycorrhizal fungi and soil in pine forests

To assess how nitrogen (N) availability affected ectomycorrhizal functioning and to test a theoretical model of ectomycorrhizal ¹⁵N partitioning, we measured C/N and δ¹⁵N in soils and nine fungal taxa in two Swedish N addition experiments. Sporocarp C/N and soil C/N decreased with fertilization, implying that N uptake per unit fungal growth increased. The S horizon was more responsive than the F and H horizons to changes in N addition, with N turnover for these horizons of 24, 57, and 57 y, respectively. Fungal and soil δ¹⁵N patterns identified fungal N sources, with N acquisition primarily from the S, F, or H horizon for two, five, and two taxa, respectively. With increasing N availability, sporocarp ¹⁵N enrichment increased in five taxa, in agreement with our model of fungal-plant N partitioning. However, it decreased in Lactarius rufus and Russula aeruginea, perhaps indicating shifts towards greater inorganic N uptake in these two taxa. This may relate to the generally lower sensitivity of these taxa to N deposition compared to the Cortinarius and Suillus taxa that fit our model of ¹⁵N partitioning.     

The influence of omnivorous elaterid larvae on the microbial carbon cycle in different forest soils

Summary Data are presented on the influence of Athous subfuscus larvae (Coleoptera, Elateridae) on the microbial carbon cycle in the biotically most active horizons of three contrasting beech forest soils: the A_h horizon of a mull soil on limestone (Göttinger Wald, FRG), the F/H horizon of a moder soil on new red sandstone (Solling area, FRG) and in the F/H horizon of a lime ameliorated area close to the second site. Gut content analyses demonstrated that the larvae of A. subfuscus are humiphagous and that this unspecific feeding behaviour is widely independent of soil conditions. Differences in ¹⁴C incorporation demonstrated that only the larvae in the F/H horizon of the limed moder soil directly affected primary decomposer organisms. However, the burrowing activity of the larvae in the topsoil indirectly modified the time course of beech leaf-litter decomposition in the litter layer of all three soils. The microflora of the mull soil contained 2.6%, that of the moder soil 0.7% and that of the limed moder soil 2.2% of total C. The metabolic quotient (qCO₂, 10°C) of the soil microflora was 0.0010 (mgCO₂-C·mg^-1 biomass-C·h^-1) in the mull soil, 0.0034 in the moder soil and 0.0012 in the limed moder soil. The A. subfuscus larvae generally reduced the size of the microbial C pool (<-30%) and increased the metabolic quotient of the microflora (>+50%). Considering these soil-independent effects of A. subfuscus on the C turnover of the soil microflora, the burrowing activity of humiphagous soil arthropods may generally increase nutrient availability to primary producers. The results of this study reveal that some of the micro- and mesoscale effects of humiphagous arthropods on the microbial carbon turnover in beech forest soils are surprisingly similar, even under very different soil conditions. The long-term modification of the time course of leaf litter decomposition, in contrast, indicates that the influence of humiphagous arthropods on the formation of the humus layer is soil-specific. There are profound differences in the role of humiphagous arthropods in limed moder soils and in naturally base-rich soils. It is concluded that liming increases competition within the microfloral population due to accelerated humification. The negative effect of A. subfuscus on ¹⁴C mineralization in the limed substrate could thus be explained by its effects on a microflora that was strongly limited by the availability of carbon.     

Foodborne Trematode Metacercariae in Fish from Northern Vietnam and Their Adults Recovered from Experimental Hamsters

The prevalence of foodborne trematode (FBT) metacercariae was investigated in fish from 2 localities of northern Vietnam in 2004-2005. Freshwater fish (9 species) were collected from local markets in Hanoi City (n=76) and Nam Dinh Province (n=79), and were examined for FBT metacercariae using the artificial digestion technique. Adult flukes were obtained from hamsters experimentally infected with the metacercariae at day 8 post-infection. Three (Haplorchis pumilio, Centrocestus formosanus, and Procerovum varium) and 6 (Haplorchis taichui, H. pumilio, C. formosanus, P. varium, Stellantchasmus falcatus, and Heterophyopsis continua) species of FBT metacercariae were detected in the 2 regions, respectively. Overall, among the positive fish species, H. pumilio metacercariae were detected in 104 (80.0%) of 130 fish examined (metacercarial density per infected fish; 64.2). C. formosanus metacercariae were found in 37 (40.2%) of 92 fish (metacercarial density; 14.7). P. varium metacercariae were detected in 19 (63.3%) of 30 fish (Anabas testudineus and Mugil cephalus) (metacercarial density; 247.7). S. falcatus metacercariae were found in all 10 M. cephalus examined (metacercarial density; 84.4). H. continua metacercariae (2 in number) were detected in 1 fish of Coilia lindmani. Morphologic characteristics of the FBT metacercariae and their experimentally obtained adults were described. The results have demonstrated that various FBT species are prevalent in northen parts of Vietnam.     

Nitrogen supply rate in Scots pine (Pinus sylvestris L.) forests of contrasting slope aspect

We studied Nitrogen (N) transformations in Pinus sylvestris forest stands in the foothills of the SE Pre-Pyrenees (NE Spain). Plots were selected in two contrasting aspects (two plots per aspect) and N supply rate was measured by the resin-core incubation technique once every three months. N leaching through litter layers (L and F horizons) was evaluated by 5 zero-tension lysimeters in each plot. NH₄ ⁺-N, NO₃ ^--N and soluble organic-N were determined in all solutions. N supply rate showed a clear seasonal pattern. Ammonification and nitrification were segregated in space and in time. While ammonification showed a peak in spring, nitrification was higher in summer. There was evidence suggesting that nitrification occurs mostly in A1 horizon. Nitrification rates differed significantly among plots. N supply rate was 12.7–23.5 kg N·ha^-1·yr^-1 but it did not differ between aspects or plots. Inorganic-N leached through litter layers was 14–17 kg N·ha^-1·yr^-1, and represented a high proportion of N supply rate. Organic-N leached through litter layers (27.8–37.0 kg N·ha^-1·yr^-1) was higher than leached inorganic-N. However, in most cases organic-N did not represent a high proportion of changes in soluble organic-N pools in H and A1 horizons (about 240 kg N·ha^-1·yr^-1). This large decrease in soluble organic-N was much greater than the increase in inorganic-N. The possible fate of these large amounts of organic-N is discussed.     

Linkage Between Culturable Mineral-Weathering Bacteria and their Weathering Effectiveness Along a Soil Profile

In this study, we used culture-dependent methodology to characterize the weathering effectiveness and community of culturable mineral-weathering bacteria in an ultisol profile. A total of 261 isolates were obtained and found to have the ability to weather biotite. The proportions of the highly effective Si and Al solubilizers were significantly higher in the D and E horizons than in the A, B, C, and F horizons, while the A, B, C, and F horizons had the similar proportion of the highly effective Si solubilizers. The B and F horizons had the lowest proportion of the highly effective Al solubilizers. The D horizon had the maximum proportion of the highly effective Fe solubilizers. Lowest proportion of the highly effective Fe solubilizers was observed in the A and F horizons. The 261 mineral-weathering isolates were affiliated with 39 bacterial species within 19 genera. Burkholderia anthina from the A and B horizons, Burkholderia stabilis from the C, D, and E horizons, and Curtobacterium citreum from the F horizon had the significantly higher ability to release Si, Al, and Fe from biotite. The results showed the diverse mineral-weathering bacteria and the linkage between the weathering species and their weathering effectiveness along a soil profile.     

Distribution and mobility of scandium and yttrium in selected types of soils in Poland

Abstract

This study was conducted to investigate the chemical speciation of yttrium and scandium in selected types of soils and also determined the total content and profile distribution of those elements. The research was performed on soil samples from forest areas in Puszcza Borecka (Poland) known as a non-contaminated site. Soil samples were collected from natural brown, lessive and rusty soil profiles.

The sequential extraction procedure was applied to separate fractions of scandium and yttrium according to the Tessier method. The range of total content of scandium and yttrium was respectively: 0.63-6.48 mg kg^-1 and 2.25 to 27.93 mg kg^-1. Scandium and yttrium occurred predominantly in residual fraction (F5) in each genetic horizon. Also both elements occurred mainly in fraction bound to organic matter (F4). The mean percentage content of scandium measured in mobile fractions (∑F1-F2) reached about 3% (in Bbr, Bt horizons) to 14% (in Bv horizons) in relation to the total content of the element in the analysed soils. The percentage content of yttrium measured in mobile fractions reached about 4% (in A, Bv horizons) to 28% in Bt horizons in relation to the total content of the element in forest soils of Puszcza Borecka.     

Fishborne Trematode Metacercariae in Freshwater Fish from Guangxi Zhuang Autonomous Region, China

A survey was performed to investigate the infection status of fishborne trematode (FBT) metacercariae in freshwater fish from Guangxi Zhuang Autonomous Region, China. A total of 307 freshwater fish of 31 species were collected from 5 administrative regions of Guangxi Zhuang Autonomous Region. They were examined by artificial digestion method from July 2003 to August 2004. No metacercariae were detected in fish from Fusui-xian. In fish from Mashan-xian and a market in Nanning, 3 species of metacercariae, Haplorchis taichui, Haplorchis pumilio, and Centrocestus formosanus, were mainly detected. Metacercariae (8 in number) of Clonorchis sinensis were found in 1 Chanodichthys dabryi purchased from a market in Nanning. In fish from Yangshuo, Metagonimus yokogawai metacercariae were detected from all 18 fish species examined. Total 13 C. sinensis metacercariae were found in 3 out of 10 Hemibarbus maculatus from Yangshuo. All 7 Zacco platypus from Yangshuo were infected with 8-112 Echinochasmus perfoliatus metacercariae. In fish from Binyang-xian, H. pumilo metacercariae were mainly detected in all 5 fish species examined, and only 1 metacercaria of C. sinensis was found in a Hemiculter leucisculus. From the above results, it was confirmed that some species of freshwater fish play a role of second intermediate hosts for FBT in Guangxi Zhuang Autonomous Region, China. In particular, 4 species of intestinal flukes, M. yokogawai, H. taichui, H. pumilio, and C. formosanus, were prevalent in fish hosts, whereas C. sinensis metacercariae were detected only in 3 fish species.     

Genetic Editing of HBV DNA by Monodomain Human APOBEC3 Cytidine Deaminases and the Recombinant Nature of APOBEC3G

Hepatitis B virus (HBV) DNA is vulnerable to editing by human cytidine deaminases of the APOBEC3 (A3A-H) family albeit to much lower levels than HIV cDNA. We have analyzed and compared HBV editing by all seven enzymes in a quail cell line that does not produce any endogenous DNA cytidine deaminase activity. Using 3DPCR it was possible to show that all but A3DE were able to deaminate HBV DNA at levels from 10⁻² to 10⁻⁵ in vitro, with A3A proving to be the most efficient editor. The amino terminal domain of A3G alone was completely devoid of deaminase activity to within the sensitivity of 3DPCR (∼10⁻⁴ to 10⁻⁵). Detailed analysis of the dinucleotide editing context showed that only A3G and A3H have strong preferences, notably CpC and TpC. A phylogenic analysis of A3 exons revealed that A3G is in fact a chimera with the first two exons being derived from the A3F gene. This might allow co-expression of the two genes that are able to restrict HIV-1Δvif efficiently.     

Ovine pedomics: the first study of the ovine foot 16S rRNA-based microbiome

We report the first study of the bacterial microbiome of ovine interdigital skin based on 16S rRNA by pyrosequencing and conventional cloning with Sanger-sequencing. Three flocks were selected, one a flock with no signs of footrot or interdigital dermatitis, a second flock with interdigital dermatitis alone and a third flock with both interdigital dermatitis and footrot. The sheep were classified as having either healthy interdigital skin (H) and interdigital dermatitis (ID) or virulent footrot (VFR). The ovine interdigital skin bacterial community varied significantly by flock and clinical condition. The diversity and richness of operational taxonomic units was greater in tissue from sheep with ID than H or VFR-affected sheep. Actinobacteria, Bacteriodetes, Firmicutes and Proteobacteria were the most abundant phyla comprising 25 genera. Peptostreptococcus, Corynebacterium and Staphylococcus were associated with H, ID and VFR, respectively. Sequences of Dichelobacter nodosus, the causal agent of ovine footrot, were not amplified because of mismatches in the 16S rRNA universal forward primer (27F). A specific real-time PCR assay was used to demonstrate the presence of D. nodosus, which was detected in all samples including the flock with no signs of ID or VFR. Sheep with ID had significantly higher numbers of D. nodosus (10⁴–10⁹ cells per g tissue) than those with H or VFR feet.     

Phytotoxic polyacetylenes from roots of Russian knapweed (Acroptilon repens (L.) DC.)

There are several factors thought to assist invasive weeds in colonization of ecosystems. One of these factors is allelopathy, the negative effect of chemicals produced by one plant on neighboring plants, frequently mediated through root exudates and other plant leachates. Acroptilon repens (Asteraceae) is one of the most invasive and ecologically threatening weed species in western North America. A bioassay-guided fractionation of the root extracts of this plant led to the isolation of five polyacetylenic compounds, of which one [5′-methoxy-1′-(5-prop-1-yn-1-yl-2-thienyl)-hexa-2′,4′-diyin-6′-yl acetate] was hitherto unknown. The structures of these compounds were elucidated on the basis of spectroscopic analysis (IR, ESIMS, ¹H, ¹³C NMR and 2D NMR). All of the compounds obtained, except 1-chloro-4-(5-penta-1,3-diyn-1-yl-2-thienyl)but-3-yn-2-ol, showed phytotoxic activity against Arabidopsis thaliana seedlings. The presence of 4′-chloro-1′-(5-penta-1,3-diyn-1-yl-2-thienyl)-but-2′-yn-3′-ol was detected in the root exudates of aeroponically grown A. repens plants. None of the polyacetylenes isolated in this study were found in Colorado soils collected between September 2006 and July 2007 in an A. repens colonized site. However, polyacetylene 5 in A. repens infested soil from Washington was found in June, 2007. Contrary to our previous report, the compound 7,8-benzoflavone (6) was not detected in root exudates, nor was it encountered in extracts of roots, aerial parts or infested soil. Since we could not repeat this work, the original report has been retracted [Stermitz, F.R., Bais, H.P., Foderaro, T.A., Vivanco, J.M., 2003. 7,8-Benzoflavone: a phytotoxin from root exudates of invasive Russian knapweed [A retraction]. Phytochemistry 64, 493-497.].     

APOBEC3G Restricts HIV-1 to a Greater Extent than APOBEC3F and APOBEC3DE in Human Primary CD4+ T Cells and Macrophages

APOBEC3 proteins inhibit HIV-1 replication in experimental systems and induce hypermutation in infected patients; however, the relative contributions of several APOBEC3 proteins to restriction of HIV-1 replication in the absence of the viral Vif protein in human primary CD4⁺ T cells and macrophages are unknown. We observed significant inhibition of HIV-1Δvif produced in 293T cells in the presence of APOBEC3DE (A3DE), APOBEC3F (A3F), APOBEC3G (A3G), and APOBEC3H haplotype II (A3H HapII) but not APOBEC3B (A3B), APOBEC3C (A3C), or APOBEC3H haplotype I (A3H HapI). Our previous studies showed that Vif amino acids Y⁴⁰RHHY⁴⁴ are important for inducing proteasomal degradation of A3G, whereas amino acids ¹⁴DRMR¹⁷ are important for degradation of A3F and A3DE. Here, we introduced substitution mutations of ⁴⁰YRHHY⁴⁴ and ¹⁴DRMR¹⁷ in replication-competent HIV-1 to generate vif mutants NL4-3 YRHHY>A5 and NL4-3 DRMR>A4 to compare the antiviral activity of A3G to the combined antiviral activity of A3F and A3DE in activated CD4⁺ T cells and macrophages. During the first 15 days (round 1), in which multiple cycles of viral replication occurred, both the NL4-3 YRHHY>A5 and NL4-3 DRMR>A4 mutants replicated in activated CD4⁺ T cells and macrophages, and only the NL4-3 YRHHY>A5 mutant showed a 2- to 4-day delay in replication compared to the wild type. During the subsequent 27 days (round 2) of cultures initiated with peak virus obtained from round 1, the NL4-3 YRHHY>A5 mutant exhibited a longer, 8- to 10-day delay and the NL4-3 DRMR>A4 mutant exhibited a 2- to 6-day delay in replication compared to the wild type. The NL4-3 YRHHY>A5 and NL4-3 DRMR>A4 mutant proviruses displayed G-to-A hypermutations primarily in GG and GA dinucleotides as expected of A3G- and A3F- or A3DE-mediated deamination, respectively. We conclude that A3G exerts a greater restriction effect on HIV-1 than A3F and A3DE.     

The relationship between occurrence of invasive bryozoan <Emphasis Type="Italic">Pectinatella magnifica</Emphasis> (Leidy 1851) and parameters of the aquatic environment in the Biosphere Reserve Třeboňsko (Czech Republic)

In the period from 2012 to 2014, twenty localities with a varying density level of the invasive bryozoan Pectinatella magnifica were investigated in the T?eboň region. These localities included water bodies ranging from eutrophic-hypertrophic fishponds to mesotrophic-oligotrophic flooded sandpits. The aim of the study was to investigate and compare the water bodies’ physical, hydrochemical and hydrobiological parameters. Control localities (localities with absence of P. magnifica) were found to be significantly different from localities with occurrence of P. magnifica in most of the measured parameters. Also shown was that P. magnifica tends to form colonies in localities showing above-average qualitative parameters within the T?eboň region: balanced oxygen and pH regime, low concentration of suspended solids (Secchi depth over 1 m) and nitrogen forms (mean TN 1.5 mg L^?1), chlorophyll-a mean concentration 54 µg L^?1, and zooplankton mean density 117 ind L^?1 and biomass 2 mg of wet weight L^?1. Furthermore, P. magnifica was also found in brown humic waters. While the sites with P. magnifica occurrence are often mesotrophic flooded sandpits and fishponds under nature protection, fishponds for recreational use, and those with low intensity of fishery management (without formation of massive cyanobacterial water blooms, oxygen regime fluctuations, etc.), localities unoccupied by invasive bryozoans are mostly strictly eutrophic-hypertrophic, semi-intensified, carp fishponds.     

Saxitoxin binding to neural membranes from pyrethroid susceptible and resistant tobacco budworm moths Heliothis virescens

1. [³H]Saxitoxin, a sodium channel probe, was found to bind reversibly with high affinity to a single class of noninteracting sites in membrane preparations from whole head homogenates of tobacco budworm, Heliothis virescens (F.), moths from a pyrethroid susceptible strain and from a pyrethroid resistant strain with nerve insensitivity and metabolic resistance mechanisms.2. No significant interstrain differences were detected in saturation (K_D, B_max) and kinetic (k₊₁, k₋₁) experiments.3. Also, five pyrethroids, two formamidines, and DDT had no significant effect on [³H]saxitoxin binding when tested at concentrations of 1 × 10⁻⁴ and 1 × 10⁻⁸ M.4. It appeared that a decreased density in sodium channels in resistant strain moths as compared with that in susceptible strain moths was not a factor in pyrethroid-induced resistance in this particular strain of tobacco budworm.     

Modeling EEG fractal dimension changes in wake and drowsy states in humans—a preliminary study

Aim of this preliminary study was to examine and compare topographic distribution of Higuchi's fractal dimension (FD, measure of signal complexity) of EEG signals between states of relaxed wakefulness and drowsiness, as well as their FD differences. The experiments were performed on 10 healthy individuals using a fourteen-channel montage. An explanation is offered on the causes of the detected FD changes. FD values of 60 s records belonging to wake (Hori's stage 1) and drowsy (Hori's stages 2-4) states were calculated for each channel and each subject. In 136 out of 140 epochs an increase in FD was obtained. Relationship between signal FD and its relative alpha amplitude was mathematically modeled and we quantitatively demonstrated that the increase in FD was predominantly due to a reduction in alpha activity. The model was generalized to include other EEG oscillations. By averaging FD values for each channel across 10 subjects, four clusters (O2O1; T6P4T5P3; C3F3F4C4F8F7; T4T3) for the wake and two clusters (O2O1P3T6P4T5; C3C4F4F3F8T4T3F7) for the drowsy state were statistically verified. Topographic distribution of FD values in wakefulness showed a lateral symmetry and a partial fronto-occipital gradient. In drowsiness, a reduction in the number of clusters was detected, due to regrouping of channels T3, T4, O1 and O2. Topographic distribution of absolute FD differences revealed largest values at F7, O1 and F3. Reorganization of channel clusters showed that regionalized brain activity, specific for wakefulness, became more global by entering into drowsiness. Since the global increase in FD during wake-to-drowsy transition correlated with the decrease of alpha power, we inferred that increase of EEG complexity may not necessarily be an index of brain activation.     

Liming and nitrogen fertilization affects phosphatase activities, microbial biomass and mycorrhizal colonisation in upland grassland

We have studied the effects of factorial combinations of lime and N additions on soil microbial biomass, respiration rates and phosphatase activity of an upland grassland. We also used an Agrostis capillaris seedling bioassay to assess the effect of the treatments on the activity of arbuscular-mycorrhizal (AM) fungi and root surface phosphatase enzymes and the concentrations of N and P in the bioassay plant shoots. In the F and H horizons, soil microbial biomass carbon (C^mic) decreased in response to the liming, while addition of lime and N together reduced basal respiration rates. In the Ah horizon, C^mic was unaffected by the treatments but basal respiration rates decreased in the plots receiving nitrogen. Soil phosphatase activity decreased only in the Ah horizon in plots receiving lime, either in combination with N or alone. The mass of root fwt. colonized by AM fungi increased in response to the treatments in the order nitrogenR²=28.7%, P=0.004). The results demonstrate the sensitivity of both free-living heterotrophic microorganisms and symbiotic mycorrhizal fungi to short-term (2 years) applications of lime and N to long-term upland grassland, particularly in relation to the key P cycling activities undertaken by these organisms.     

Synthesis of pyrazole encompassing 2-pyridone derivatives as antibacterial agents

A series of novel compounds 6-amino-1-((1,3-diphenyl-1H-pyrazole-4-yl)methyleneamino)-4-(aryl)-2-oxo-1,2-dihydropyridine-3,5-dicarbonitriles (4a–t) were synthesized and characterized by IR, ¹H NMR, ¹³C NMR and mass spectral data. These compounds were screened for their in vitro antibacterial activity against Staphylococcus aureus, Streptococcus pyogenes (Gram positive), Escherichia coli, Pseudomonas aeruginosa (Gram negative) by serial broth dilution and cytotoxic activity (NIH 3T3 & HeLa) by MTT assay. The results indicated that compounds 4g, 4i, 4m, 4o, 4r and 4t exhibit potent antibacterial activity against bacterial strains at non-cytotoxic concentrations.     

Bioconcentration of Cd and Zn in the soils of an uncontaminated forest in the Quebec Laurentians

Fine-scale trace element (TE) concentration patterns exist in soils that were never exposed to the direct deposition of TE in the past. We aimed to understand the role of vegetation, in particular trees, in defining these spatial patterns in the soil horizons of an uncontaminated forest ecosystem. Living tree leaves and surface soil samples (L, F, and B horizons) were collected from a ca. 1400 m² plot in the Hermine watershed where a strong gradient in the abundance of Yellow birches (Betula alleghaniensis—BA) exists. TE analysis showed that BA leaves had up to 13 times more Cd and Zn than the other tree species. Significantly similar spatial patterns were detected between the density of BA trunks, the abundance of BA leaves in the litter (L) layer, and Cd and Zn concentrations in the F horizon. The opposite trend was found in the upper B horizon, where Cd and Zn were depleted under a denser BA canopy. We submit that soil depletion could be associated with the preferential phytoextraction of Cd and Zn by BA over a period of several decades. Our study stresses the role of biological cycling by trees on the profile redistribution and the generation of patterns of soil TE in quasi-pristine forests.

     

Characterization of Shiga toxin-producing Escherichia coli isolated from healthy pigs in China

Background

Shiga toxin-producing Escherichia coli (STEC) is recognized as an important human diarrheal pathogen. Swine plays an important role as a carrier of this pathogen. In this study we determined the prevalence and characteristics of STEC from healthy swine collected between May 2011 and August 2012 from 3 cities/provinces in China.

Results

A total of 1003 samples, including 326 fecal, 351 small intestinal contents and 326 colon contents samples, was analyzed. Two hundred and fifty five samples were stx-positive by PCR and 93 STEC isolates were recovered from 62 stx-positive samples. Twelve O serogroups and 19 O:H serotypes including 6 serotypes (O100:H20/[H20], O143:H38/[H38], O87:H10, O172:H30/[H30], O159:H16, O9:H30/[H30]) rarely found in swine and ruminants were identified. All 93 STEC isolates harbored stx ₂ only, all of which were stx _2e subtype including 1 isolate being a new variant of stx _2e. 53.76%, 15.05% and 2.15% STEC isolates carried astA, hlyA and ehxA respectively. Four STEC isolates harbored the high-pathogenicity island. Of the 15 adherence-associated genes tested, 13 (eae, efa1, iha, lpfA _O113, lpfA _O157/OI-154, lpfA _O157/OI-141, toxB, saa, F4, F5, F6, F17 or F41) were all absent while 2 (paa and F18) were present in 7 and 4 STEC isolates respectively. The majority of the isolates were resistant to tetracycline (79.57%), nalidixic acid (78.49%), trimethoprim-sulfamethoxazole (73.12%) and kanamycin (55.91%). The STEC isolates were divided into 63 pulsed-field gel electrophoresis patterns and 21 sequence types (STs). Isolates of the same STs generally showed the same or similar drug resistance patterns. A higher proportion of STEC isolates from Chongqing showed multidrug resistance with one ST (ST3628) resistant to 14 antimicrobials.

Conclusions

Our results indicate that swine is a significant reservoir of STEC strains in China. Based on comparison by serotypes and sequence types with human strains and presence of virulence genes, the swine STEC may have a low potential to cause human disease.     

Genome-Based Analysis and Gene Dosage Studies Provide New Insight into 3-Hydroxy-4-Methylvalerate Biosynthesis in Ralstonia eutropha

Recombinant Ralstonia eutropha strain PHB⁻4 expressing the broad-substrate-specificity polyhydroxyalkanoate (PHA) synthase 1 from Pseudomonas sp. strain 61-3 (PhaC1_Ps) synthesizes a PHA copolymer containing the branched side-chain unit 3-hydroxy-4-methylvalerate (3H4MV), which has a carbon backbone identical to that of leucine. Mutant strain 1F2 was derived from R. eutropha strain PHB⁻4 by chemical mutagenesis and shows higher levels of 3H4MV production than does the parent strain. In this study, to understand the mechanisms underlying the enhanced production of 3H4MV, whole-genome sequencing of strain 1F2 was performed, and the draft genome sequence was compared to that of parent strain PHB⁻4. This analysis uncovered four point mutations in the 1F2 genome. One point mutation was found in the ilvH gene at amino acid position 36 (A36T) of IlvH. ilvH encodes a subunit protein that regulates acetohydroxy acid synthase III (AHAS III). AHAS catalyzes the conversion of pyruvate to 2-acetolactate, which is the first reaction in the biosynthesis of branched amino acids such as leucine and valine. Thus, the A36T IlvH mutation may show AHAS tolerance to feedback inhibition by branched amino acids, thereby increasing carbon flux toward branched amino acid and 3H4MV biosynthesis. Furthermore, a gene dosage study and an isotope tracer study were conducted to investigate the 3H4MV biosynthesis pathway. Based on the observations in these studies, we propose a 3H4MV biosynthesis pathway in R. eutropha that involves a condensation reaction between isobutyryl coenzyme A (isobutyryl-CoA) and acetyl-CoA to form the 3H4MV carbon backbone.