Colonization of secondary woodlands by Anemone nemorosa

Migration of the herb species Anemone nemorosa from older woodlands into adjacent, recently established deciduous woodlands on former arable land was studied. The wood anemone had colonized part of all studied recent woods, varying in age between 30 and 75 years. Cover of A. nemorosa in the recent woods decreased with increasing distance from the older woodland at all sites but one, indicating dispersal limitation during colonization. The advancing edge of most populations was characterized by negative logarithmic decrease in cover with establishment of isolated pioneer individuals and later gradual infill between pioneers. Migration rates were calculated by three methods. The mean migration rate of A. nemorosa based on observed maximum cover in the recent woods was 0.20 m year¹, 0.40 m year^-1 based on half maximum cover and 0.85 m year¹ based on the individual found farthest from the former woodland border. The calculated migration rates were consistently higher than the rate of possible rhizome growth. Seed dispersal and establishment is thus very important for colonization of new woodlands. Migration rates increased with tree canopy cover–especially cover of broad-leaved species with quickly decomposing litter–and with soil pH. Migration rates decreased with increasing grass cover in the field layer. These differences in migration rates may be due to increased micro-site availability for establishment at high canopy cover, low grass cover and high soil pH. Our results show that the wood anemone generally colonizes recent woods from nearby source populations. However, colonization proceeds relatively slowly and is limited by both seed dispersal and availability of suitable micro-sites. Gradients in abundance of A. nemorosa within secondary woods may be detectable for long periods of time and indicate the recent origin of a woodland.     

The demise of Leptotheca Thélohan, 1895 (Myxozoa: Myxosporea: Ceratomyxidae) and assignment of its species to Ceratomyxa Thélohan, 1892 (Myxosporea: Ceratomyxidae), Ellipsomyxa K?ie, 2003 (Myxosporea: Ceratomyxidae), Myxobolus Bütschli, 1882 and Sphaerospora Thélohan, 1892 (Myxosporea: Sphaerosporidae)

A revision of Leptotheca Thélohan, 1895 is presented. The boundaries that separate Leptotheca from Ceratomyxa Thélohan, 1892 and Sphaerospora Thélohan, 1892 are vague and have been highlighted as an area of concern within myxosporean classification. A survey of the literature revealed 63 species that are currently assigned to Leptotheca and a further 11 species that have been relegated as synonyms in Ceratomyxa, Sphaerospora or Myxobolus Bütschli, 1882. The placement of some species in the genus is unclear and demonstrates the need for a revision. The type-species of Leptotheca (L. agilis Thélohan 1892) has many Ceratomyxa-like characters, such that a minor amendation of the diagnosis of Ceratomyxa will then accept the type-species of Leptotheca, rendering the latter genus its synonym. We propose the suppression of Leptotheca, with all species currently assigned to that genus reassigned to Ceratomyxa, Ellipsomyxa K?ie, 2003, Myxobolus or Sphaerospora on the basis of appropriate morphological and biological traits. The diagnoses of Ceratomyxa and Ellipsomyxa are amended appropriately. Molecular analysis may change the placement of some species in the future; however, the aim of this review was to eliminate the ambiguity of assignment of species in the genera Leptotheca, Ceratomyxa and Sphaerospora by suppressing Leptotheca.     

Enzymes in the biosynthesis of aromatic polyketide antibiotics

Aromatic polyketides are secondary metabolites that afford some of the most common antibiotics and anti-cancer drugs currently in clinical use. Not least because of their medical importance, the biosynthesis of these compounds has attracted considerable interest during the past few years; important advances have been made in the structural and mechanistic characterisation of the enzymes involved. These studies are expected to have implications for the production of novel therapeutic agents by combinatorial biosynthesis.     

Clinical Utility of a Commercial LAM-ELISA Assay for TB Diagnosis in HIV-Infected Patients Using Urine and Sputum Samples

Background

The accurate diagnosis of TB in HIV-infected patients, particularly with advanced immunosuppression, is difficult. Recent studies indicate that a lipoarabinomannan (LAM) assay (Clearview-TB®-ELISA) may have some utility for the diagnosis of TB in HIV-infected patients; however, the precise subgroup that may benefit from this technology requires clarification. The utility of LAM in sputum samples has, hitherto, not been evaluated.

Methods

LAM was measured in sputum and urine samples obtained from 500 consecutively recruited ambulant patients, with suspected TB, from 2 primary care clinics in South Africa. Culture positivity for M. tuberculosis was used as the reference standard for TB diagnosis.

Results

Of 440 evaluable patients 120/387 (31%) were HIV-infected. Urine-LAM positivity was associated with HIV positivity (p = 0.007) and test sensitivity, although low, was significantly higher in HIV-infected compared to uninfected patients (21% versus 6%; p<0.001), and also in HIV-infected participants with a CD4 <200 versus >200 cells/mm³ (37% versus 0%; p = 0.003). Urine-LAM remained highly specific in all 3 subgroups (95%–100%). 25% of smear-negative but culture-positive HIV-infected patients with a CD4 <200 cells/mm³ were positive for urine-LAM. Sputum-LAM had good sensitivity (86%) but poor specificity (15%) likely due to test cross-reactivity with several mouth-residing organisms including actinomycetes and nocardia species.

Conclusions

These preliminary data indicate that in a high burden primary care setting the diagnostic usefulness of urine-LAM is limited, as a rule-in test, to a specific patient subgroup i.e. smear-negative HIV-infected TB patients with a CD4 count <200 cells/mm³, who would otherwise have required further investigation. However, even in this group sensitivity was modest. Future and adequately powered studies in a primary care setting should now specifically target patients with suspected TB who have advanced HIV infection.     

Three-dimensional reconstruction of a human metaphase chromosome from electron micrographs

A complete human metaphase chromosome has been reconstructed from a series of electron microscopical projections obtained by tilting the specimen stage at 3 degree intervals from –60 to +60 degrees. The reconstructed structure is about 3.0 m long, 1.6 m wide, and 0.8 m thick. The mass distribution was fairly homogeneous within the chromatids and neither a hollow nor a dense core was observed. The distribution and course of fibers observed are most consistent with a looping model of chromosome structure.     

Immunogenicity of plant‐produced porcine circovirus‐like particles in mice

Porcine circovirus type 2 (PCV‐2) is the main causative agent associated with a group of diseases collectively known as porcine circovirus‐associated disease (PCAD). There is a significant economic strain on the global swine industry due to PCAD and the production of commercial PCV‐2 vaccines is expensive. Plant expression systems are increasingly regarded as a viable technology to produce recombinant proteins for use as pharmaceutical agents and vaccines. However, successful production and purification of PCV‐2 capsid protein (CP) from plants is an essential first step towards the goal of a plant‐produced PCV‐2 vaccine candidate. In this study, the PCV‐2 CP was transiently expressed in Nicotiana benthamiana plants via agroinfiltration and PCV‐2 CP was successfully purified using sucrose gradient ultracentrifugation. The CP self‐assembled into virus‐like particles (VLPs) resembling native virions and up to 6.5 mg of VLPs could be purified from 1 kg of leaf wet weight. Mice immunized with the plant‐produced PCV‐2 VLPs elicited specific antibody responses to PCV‐2 CP. This is the first report describing the expression of PCV‐2 CP in plants, the confirmation of its assembly into VLPs and the demonstration of their use to elicit a strong immune response in a mammalian model.     

Some novel flavin-nicotinamide biscoenzymes and their reactivities

The present study was undertaken to investigate flavin-nicotinamide reactions and interactions. A series of novel flavin-nicotinamide biscoenzymes have been synthesized by a general three-step procedure. The structures of these compounds were confirmed by nuclear magnetic resonance spectra, absorption spectra and elemental analysis. These compounds consist of short linear hydrocarbon chains interconnecting the N-1 of nicotinamide and the N-10 of the 7,8-dimethyl-isoalloxazine ring. The compounds were reduced with sodium dithionite (Na₂S₂O₄) and the flavin portion was reoxidized with ferricyanide. Re-reduction of the flavin portion by the nicotinamide portion of the molecule was followed anaerobically at 442 nm. When the interconnecting hydrocarbon chain was unsaturated, a second order reaction was observed with a rate equal to that of lumiflavin and 1-propyl-1,4-dihydronicotinamide (NprNicH₂) under the same conditions. When the two halves of the biscoenzymes were connected by saturated three- and four-carbon chains, the expected unimolecular reaction was not observed. Instead, the reduced biscoenzyme, after separation from excess sodium dithionite, was shown to have a strong absorption at 298 nm. This absorption is characteristic of hydration of dihydronicotinamides at the 5,6-double bond.In further studies, the C₃-biscoenzyme exhibited an absorption at 600 nm due to a complex between the reduced flavin and oxidized nicotinamide portions of the molecule. Absorbance at 600 nm increased linearly with the C₃-biscoenzyme concentration, clearly indicating that this is an intramolecular complex. When the C₃-biscoenzyme was at 0°C in 60–75% dimethylformamide buffer solution, no absorption at 600 nm was observed. When excess dithionite was removed, the spectrum under these conditions showed definite peaks at 297 and 357 nm. These respective peaks were attributed to hydrated dihydronicotinamide and dihydronicotinamide species present in the reaction mixture.The reduced flavin was postulated to be a catalyst for the hydration of dihydronicotinamide. This hypothesis was tested by incubating 1-propyl-1,4-dihydronicotinamide alone and with several concentrations of reduced riboflavin under basic anaerobic conditions. The results show that the reduced flavin increases the rate of disappearance of the dihydronicotinamide species and that the product shows an absorption near 298 nm. These results indicate that a reduced form of the flavin nucleus catalyzes the hydration of dihydronicotinamides.