Towards a more transparent use of the potential natural vegetation concept – an answer to Chiarucci et al.

In this paper, the concerns of Chiarucci et al. ( 2010 ) regarding use of the potential natural vegetation (PNV) concept are addressed, as voiced in the forum section of the Journal of Vegetation Science. First, we rectify some unfounded expectations concerning PNV, including a relationship with prehuman vegetation and phytosociology. Second, we point out issues that pose considerable challenges in PNV and require common agreement. Here, we address the issue of time and disturbance. We propose to use the static PNV concept as a baseline, a null model for landscape assessment and in comparisons. Instead of changing the PNV concept itself, we introduce a new term, potential future natural vegetation (PFV) to cover estimations of potential successional outcomes. Finally, we offer a new view of PNV with which we intend to make the use of PNV estimates more transparent. We formalize the PNV theory into a partial cause‐effect model of vegetation that clearly states which effects on vegetation are factored out during its estimation. Further, we also propose to assess PNV in a probabilistic setting, rather than providing a single estimate for one location. This multiple PNV would reflect our uncertainty about the vegetation entity that could persist at the locality concerned. Such uncertainty arises from the overlap of environmental preferences of different mature vegetation types. Thus reformulated, we argue that the PNV concept has much to offer as a null model, especially in landscape ecology and in site comparisons in space and time.     

Acanthocheilonema sabanicolae n. sp. (Filarioidea: Onchocercidae) from the savanna armadillo (Dasypus sabanicola) in Venezuela, with comments on the genus Acanthocheilonema

A new species of Acanthocheilonema, Acanthocheilonema sabanicolae n. sp., is described from the subcutaneous tissues of the savanna armadillo (Dasypus sabanicola) in Venezuela. The adults (females 25-30.6 mm long by 61-78 micron wide; males 10.9-15.3 mm long by 42-44 micron wide) and the microfilariae (112-131 micron long by 3-5 micron wide) are the smallest within the genus. The microfilaria, a skin dweller, assumes a characteristic C-shaped curve, when fixed in 2% formalin, which serves to distinguish A. sabanicolae from others in the genus. Moreover, the spicules are notably smaller than any others in the Acanthocheilonema. Acanthocheilonema sabanicolae is the first species in this genus to be described from edentates, and, along with A. reconditum of dogs and A. pricei of opossums, is the third species of Acanthocheilonema to be reported from South America. Morphological features, vectors, and vertebrate hosts of the genus Acanthocheilonema are reviewed.     

Quantitative investigations of amperometric spike feet suggest different controlling factors of the fusion pore in exocytosis at chromaffin cells

Around 30% of exocytosis events recorded by amperometry at carbon fiber microelectrodes exhibit a pre-spike feature (PSF) termed a “foot”. This wave is associated with the release of the neurotransmitters via a transitory fusion pore, whilst the large, main exocytotic spike is due to complete release. The amperometric data reported herein were obtained using bovine chromaffin cells stimulated with either potassium or barium ions, two commonly-employed elicitors of exocytosis. Identical trends are observed with both activators: (i) they induce the same ratio (close to 30%) of events with a foot in the population of amperometric spikes, and (ii) spikes with a foot can be divided into two primary categories, depending on the temporal variation of the current wave (viz. as a ramp, or a ramp followed by a plateau). Correlations between the characteristics of the whole current spike, and of its observed foot, have been sought; such analyses demonstrate that the maximum current of both foot and spike signals are highly correlated, but, in contrast, the integrated charges of both are poorly correlated. Moreover, the temporal duration of the PSF is fully uncorrelated with any parameter pertaining to the main current spike. On the basis of these reproducible observations, it is hypothesized that the characteristics (dimensions and topology, at least) of each secretory vesicle determine the probability of formation of the fusion pore and its maximum size, whilst molecular factors of the cell membrane control its duration, and, consequently, the amount delivered prior to the massive exocytosis of catecholamines observed as a spike in amperometry.     

Acquisition of Iron by Alkaliphilic Bacillus Species

The biochemical and molecular mechanisms used by alkaliphilic bacteria to acquire iron are unknown. We demonstrate that alkaliphilic (pH > 9) Bacillus species are sensitive to artificial iron (Fe³⁺) chelators and produce iron-chelating molecules. These alkaliphilic siderophores contain catechol and hydroxamate moieties, and their synthesis is stimulated by manganese(II) salts and suppressed by FeCl₃ addition. Purification and mass spectrometric characterization of the siderophore produced by Caldalkalibacillus thermarum failed to identify any matches to previously observed fragmentation spectra of known siderophores, suggesting a novel structure.Iron is an abundant element in nature; however, in most aqueous aerobic environments iron forms insoluble ferric hydroxide, Fe(OH)₃. This poses a major problem for most aerobic bacteria, as ferric hydroxide has a solubility constant of 10⁻³⁹ M, therefore limiting the concentration of ferric ions to 10⁻¹⁸ M at pH 7.0. For example, bacteria living in seawater (approximate pH 8.0) require iron, yet dissolved iron is only present at 0.02 to 2.0 nM (5). Despite this apparent lack of bioavailability, iron has been repeatedly demonstrated to be an essential element for aerobic bacterial growth (1).With the lack of readily accessible iron at physiological pH, most bacteria have evolved systems to deal with the incumbent problem of iron acquisition. Under iron-rich conditions, Fe²⁺ uptake receptors, such as FeoAB, are synthesized in bacteria, which passively import iron in the immediate vicinity of the cell (1, 23). No equivalent system has been identified for Fe³⁺ transport. To acquire Fe³⁺ under aqueous aerobic conditions, bacteria commonly have import systems involving the synthesis, secretion, and regathering of a group of secondary metabolites known as siderophores (1, 11). Siderophores are low-molecular-weight chemical moieties that chelate Fe³⁺ and typically have complex formation (K_f) constants in the range of 10²³ to 10⁵² (11). Siderophores, like other chelators, are known to increase the solubility of iron by hindering the formation of Fe-oxyhydroxides at high pH, at which the Fe-oxyhydroxides are the dominating inorganic species (27). Siderophores are also known to facilitate the dissolution of Fe from minerals (3). Siderophore-iron complexes can either be transported through cellular membranes using dedicated transport systems or if the Fe(III) central atom is reduced, making the iron bioavailable for cellular processes (10, 14). Three major groups of siderophores have been described in bacteria: hydroxamates, catecholates, and carboxylates. Hydroxamates and catechols are commonly produced by aerobic bacteria living at neutral to alkaline pH, whereas carboxylates are significantly more common in bacteria living in mildly acidic pH (11-13). In the genus Bacillus, Bacillus megaterium and Bacillus subtilis are producers of schizokinen and bacillibactin, respectively (6, 20). Bacillus anthracis produces both a catechol and a hydroxamate siderophore (7, 34), and B. licheniformis strain VK21 is the only known example of a thermoresistant catecholate-producing Gram-positive bacterium (32).Although there is extensive literature on iron capture mechanisms in bacteria that thrive at neutral pH, there is little information at a biochemical or molecular level on how aerobic bacteria growing at extreme alkaline pHs (i.e., pH 9 to 11) acquire iron. At alkaline pH, the solubility constant for iron decreases far below the requirement for living cells, and the concentration of bioavailable iron is estimated to be approximately 10⁻²³ M at pH 10 (11). Taking this extreme lack of iron into account, the sequestering mechanisms of alkaliphilic bacteria must be powerful, yet there has been little analysis of the types of iron-chelating molecules these bacteria produce.     

The Trypanosoma cruzi nucleolus: a morphometrical analysis of cultured epimastigotes in the exponential and stationary phases

Our group is interested in rRNA and ribosome biogenesis in the parasitic protozoan Trypanosoma cruzi. Epimastigotes represent an extracellular replicative stage of T. cruzi and can be cultured in axenic media. The growth curve of epimastigotes allows assessment of potential differences in the nucleoli of cells undergoing growth-rate transitions. To establish cellular parameters for studying ribosome biogenesis in T. cruzi, a morphometric analysis of the nucleoli of cultured cells in the exponential and stationary phases was conducted. Electron micrograph-based measurements of nuclear sections from independent cells demonstrated that the nucleolar area is over twofold higher in exponentially growing cells, as compared with epimastigotes in the stationary phase. The granular component of the nucleoli of actively growing cells was the main structural element. Cycloheximide moderately reduced the apparent size of the nucleoli without an apparent disruption of their architecture. Our results provide a firm basis for the establishment of an experimental model to study the organization of the nucleolus during the growth and development of T. cruzi.     

A new two-color Fab labeling method for autoantigen protein microarrays

Antigen microarrays hold great promise for profiling the humoral immune response in the settings of autoimmunity, allergy and cancer. This approach involves immobilizing antigens on a slide surface and then exposing the array to biological fluids containing immunoglobulins. Although these arrays have proven extremely useful as research tools, they suffer from several sources of variability. To address these issues, we have developed a new two-color Fab labeling method that allows two samples to be applied simultaneously to the same array. This straightforward labeling approach improves reproducibility and reliably detects changes in autoantibody concentrations. Using this technique we profiled serum from a mouse model of systemic lupus erythematosus (SLE) and detected both expected and previously unrecognized reactivities. The improved labeling and detection method described here overcomes several problems that have hindered antigen microarrays and should facilitate translation to the clinical setting.     

Identification of novel small-molecule Ulex europaeus I mimetics for targeted drug delivery

Lectin mimetics have been identified that may have potential application towards targeted drug delivery. Synthetic multivalent polygalloyl constructs effectively competed with Ulex europaeus agglutinin I (UEA1) for binding to intestinal Caco-2 cell membranes.     

Changes in predictor influence with time and with vegetation type identity in a post-abandonment situation

Variation in the explanatory potential of separate variable groups describing past vegetation patterns and/or abiotic environment were investigated using data from two points in time for three vegetation types, which are variants of the steppe grassland component of the forest steppe biome. First, we compared the predictive power of environmental variables assessed by the performance of generalised linear models (GLMs) explaining the distribution of three vegetation types in 1988 and 2002. Second, we fitted models based on conceptual hypotheses to explain vegetation distribution in 2002. Specifically, we wanted to examine, whether (i) current abiotic topo-environment, (ii) past neighbourhood configuration, or (iii) historical vegetation patterns or a combination of these determine best the current distribution of vegetation types. We developed basic predictor sets for each hypothesis, and using GLMs we tested to what degree these predictor sets were capable of explaining the currently observed patterns of individual vegetation types. We compared model accuracy by AUC and TSS values. Predictive performance of models changed both with time and with vegetation type. The analyses of changes over time showed that two of the three vegetation types had come closer to an equilibrium with abiotic conditions, while the third had moved farther away from equilibrium. Knowledge of past conditions was sufficient to predict the distribution of one of the three investigated vegetation types alone, thus no topo-environmental predictors were needed to successfully predict this type. The other two vegetation types were best explained by current topo-environmental predictors. We conclude that historical conditions clearly improve predictive models, though there may be variation in their contribution to models of different vegetation types and this may depend on how far vegetation types are from an equilibrium state.