Long-term effects of fire frequency and season on herbaceous vegetation in savannas of the Kruger National Park,South Africa

Aim s: The long-term effects of changing fire regimes on the herbaceous component of savannas are poorly understood but essential for understanding savanna dynamics. We present results from one of the longest running (>44 years) fire experiments in savannas, the experimental burn plots (EBPs), which is located in the Kruger National Park (South Africa) and encompasses four major savanna vegetation types that span broad spatial gradients of rainfall (450–700 mm) and soil fertility.Methods: Herbaceous vegetation was sampled twice in the EBPs using a modified step-point method, once prior to initiation of the experiment (1954) and again after 44–47 years. Different combinations of three fire frequency (1-, 2- and 3-year return intervals) and five season (before the first spring rains, after the first spring rains, mid-summer, late summer and autumn) treatments, as well as a fire exclusion treatment, were applied at the plot level (~7 ha each), with each treatment (n = 12 total) replicated four times at each of the four sites (n = 192 plots total). The effects of long-term alterations to the fire regime on grass community structure and composition were analyzed separately for each site.Important Findings: Over the 44+ years duration of the experiment, fires were consistently more intense on sites with higher mean annual rainfall (>570 mm), whereas fires were not as intense or consistent for sites with lower and more variable rainfall (<510 mm) and potentially higher herbivory due to greater soil fertility. Because the plots were open to grazing, the impacts of herbivory along with more variable rainfall regimes likely minimized the effects of fire for the more arid sites. As a consequence, fire effects on grass community structure and composition were most marked for the higher rainfall sites and generally not significant for the more arid sites. For the high-rainfall sites, frequent dry season fires (1- to 3-year return intervals) resulted in high grass richness, evenness and diversity, whereas fire exclusion and growing season fires had the lowest of these measures and diverged the most in composition as the result of increased abundance of a few key grasses. Overall, the long-term cumulative impacts of altered fire regimes varied across broad climatic and fertility gradients, with fire effects on the grass community decreasing in importance and herbivory and climatic variability likely having a greater influence on community structure and composition with increasing aridity and soil fertility.     

Resilience and elasticity of intertidal communities in response to harvesting of the alien mussel Mytilus galloprovincialis

Besides the direct impacts of exploitation on target species, indirect effects on non-target species are unavoidable and find expression in changes in community structure. We quantified the effects of experimental harvesting of Mytilus galloprovincialis on intertidal communities on the South African west coast. In the mid- and low-shore, four months of harvesting at intensities greater than F = 0.3 and F = 0.6 respectively, resulted in significant changes in community composition. These changes were driven by progressively greater spatial dominance by the macroalgae Cladophora flagelliformis, Porphyra capensis and Ulva species as harvesting intensity increased. Four months after cessation of harvesting, community structure had not recovered and even areas subjected to as little as F = 0.3 supported significantly altered communities in both zones. The fact that substantial community changes were induced by even low-intensity exploitation is indicative of low resilience to harvesting. The densities and cover of the dominant taxa returned to a pre-harvest state 16 months after the cessation of harvesting, but multivariate analyses indicated that the overall community composition required 32 months for Cover Letter full recovery. Although these communities displayed elasticity within three years, it is recommended that should a M. galloprovincialis fishery be established in the region, harvesting be implemented at a maximum intensity of F = 0.3. This approach would maximise yields and protect associated intertidal communities.     

<Emphasis Type="Italic">Emergomyces</Emphasis>: a New Genus of Dimorphic Fungal Pathogens Causing Disseminated Disease among Immunocompromised Persons Globally

Purpose of Review

The emergence of a group of previously unknown or unrecognized dimorphic fungal species causing systemic human disease resulted in taxonomic shifts and the creation of a new genus, Emergomyces, within Onygenales. We review the morphology, taxonomy, physiology, and ecology of Emergomyces spp., and the epidemiology, clinicopathology, diagnosis, and management of disease.

Recent Findings

Emergomyces species have been reported as causes of human disease in Europe, Asia, Africa, and North America. Es. pasteurianus is most cosmopolitan, and Es. africanus, in southern Africa, causes the largest reported disease burden; in fact, emergomycosis is the most common endemic mycosis diagnosed in South Africa. The classic clinical picture is of disseminated disease, often with cutaneous involvement, in immunocompromised individuals.

Summary

Members of the genus Emergomyces are uncommon but important agents of systemic disease in immunocompromised hosts worldwide. Knowledge gaps include the biology of the fungus, and the pathophysiology and management of disease.

     

Host–plant relationships and natural enemies of the invasive mealybug,Rastrococcus iceryoides Green in Kenya and Tanzania

The invasive mango mealybug, Rastrococcus iceryoides Green (Hemiptera: Pseudococcidae), believed to be native to southern Asia has rapidly invaded Kenya and Tanzania. A survey was carried out from February 2008 to July 2009 to study its geographical distribution, host–plant relationships and associated parasitoids in both countries. Our results infer that R. iceryoides is widely distributed across the coastal belts of both countries. Rastrococcus iceryoides was recorded from 29 cultivated and wild host plants from 16 families. Twenty‐one of these host plants are new records. Among the cultivated host plants, M. indica (407.68 ± 9.26/twig and 75.68 ± 7.13/leaf in Kibaha, and 595.86 ± 17.2/fruit in Kinondoni) and Cajanus cajan (L.) Millspaugh (18.15 ± 4.22/leaf and 233.62 ± 18.9/twig in Morogoro) recorded the highest levels of infestation. Parkinsonia aculeata (394.62 ± 11.7/twig, 0.15 ± 0.03/leaf and 8.44 ± 0.94/fruit in Kinango), Caesalpinia sepiaria Roxb. (3.33 ± 0.76/leaf and 155.81 ± 9.16/twig in Kinondoni) and Deinbollia borbonica Scheff. (2.70 ± 0.66/leaf and 112.65 ± 5.3/twig in Kibaha) were found to be the most heavily infested wild host plants. Six parasitoid species were recovered and are reported here for the first time to parasitize R. iceryoides. Anagyrus pseudococci Girault was the most dominant species accounting for 21% parasitism on M. indica and 20% parasitism on P. aculeata in Tanzania and Kenya, respectively. Despite this, the ability of the parasitoid to regulate the population of R. iceryoides was inadequate. Therefore, there is a need for foreign exploration and introduction of efficient coevolved natural enemies from its aboriginal home of southern Asia to minimize its impact on horticulture in Africa.     

Targeting the cell wall of Mycobacterium tuberculosis: a molecular modeling investigation of the interaction of imipenem and meropenem with L,D-transpeptidase 2

The single crystal X-ray structure of the extracellular portion of the L,D-transpeptidase (ex-Ldt_Mt2 – residues 120–408) enzyme was recently reported. It was observed that imipenem and meropenem inhibit activity of this enzyme, responsible for generating L,D-transpeptide linkages in the peptidoglycan layer of Mycobacterium tuberculosis. Imipenem is more active and isothermal titration calorimetry experiments revealed that meropenem is subjected to an entropy penalty upon binding to the enzyme. Herein, we report a molecular modeling approach to obtain a molecular view of the inhibitor/enzyme interactions. The average binding free energies for nine commercially available inhibitors were calculated using MM/GBSA and Solvation Interaction Energy (SIE) approaches and the calculated energies corresponded well with the available experimentally observed results. The method reproduces the same order of binding energies as experimentally observed for imipenem and meropenem. We have also demonstrated that SIE is a reasonably accurate and cost-effective free energy method, which can be used to predict carbapenem affinities for this enzyme. A theoretical explanation was offered for the experimental entropy penalty observed for meropenem, creating optimism that this computational model can serve as a potential computational model for other researchers in the field.     

Interactions between Fusarium species from sugarcane and the stalk borer, Eldana saccharina (Lepidoptera: Pyralidae)

In this study, beneficial relationships between Fusarium species in sugarcane and the stalk borer, Eldana saccharina (Lepidoptera: Pyralidae) were demonstrated in vitro . In addition, Fusarium species with antagonistic properties were found to inhabit sugarcane. Attenuated Fusarium isolates from sugarcane stalks collected across the South African sugar industry were incorporated into diet formulated to mass rear E. saccharina . Of the over 200 Fusarium isolates obtained, 10 that significantly improved the survival and development of E. saccharina larvae and considered to be beneficial were selected for further study, as were 10 that were detrimental or antagonistic to the stalk borer. Twelve of the selected isolates were identified as F. sacchari by direct sequencing of translation elongation factor-1α fragments, eight of which resulted in reduced numbers of surviving larvae and significantly lower larval masses. F. proliferatum isolates resulted in increased survival and mass of E. saccharina and three of the five isolates assigned to the F. pseudonygamai group enhanced E. saccharina development. Results from olfactory choice experiments suggested the production of attractive and repellent metabolites by certain isolates. Findings from this study may offer additional or alternative strategies for managing E. saccharina infestation of sugarcane.     

A Review of the Advancements in Probiotic Delivery: Conventional vs. Non-conventional Formulations for Intestinal Flora Supplementation

Probiotic delivery systems are widely used nutraceutical products for the supplementation of natural intestinal flora. These delivery systems vary greatly in effectiveness to exert health benefits for a patient. Probiotic delivery systems can be categorized into conventional, pharmaceutical formulations, and non-conventional, mainly commercial food-based, products. The degree of health benefits provided by these probiotic formulations varies in their ability to deliver viable, functional bacteria in large enough numbers (effectiveness), to provide protection against the harsh effects of the gastric environment and intestinal bile (in vivo protection), and to survive formulation processes (viability). This review discusses the effectiveness of these probiotic delivery systems to deliver viable functional bacteria focusing on the ability to protect the encapsulated probiotics during formulation process as well as against harsh physiological conditions through formulation enhancements using coatings and polymer enhancements. A brief overview on the health benefits of probiotics, current formulation, patient and legal issues facing probiotic delivery, and possible recommendations for the enhanced delivery of probiotic bacteria are also provided. Newer advanced in vitro analyses that can accurately determine the effectiveness of a probiotic formulation are also discussed with an ideal probiotic delivery system hypothesized through a combination of the two probiotic delivery systems described.     

Bioreduction of platinum salts into nanoparticles: a mechanistic perspective

A mechanism for the bioreduction of H₂PtCl₆ and PtCl₂ into platinum nanoparticles by a hydrogenase enzyme from Fusarium oxysporum is proposed. Octahedral H₂PtCl₆ is too large to fit into the active region of the enzyme and, under conditions optimum for nanoparticle formation (pH 9, 65°C), undergoes a two-electron reduction to PtCl₂ on the molecular surface of the enzyme. This smaller molecule is transported through hydrophobic channels within the enzyme to the active region where, under conditions optimal for hydrogenase activity (pH 7.5, 38°C) it undergoes a second two-electron reduction to Pt(0). H₂PtCl₆ was unreactive at pH 7.5, 38°C; PtCl₂ was unreactive at pH 9, 65°C.     

Genetic diversity of <Emphasis Type="Italic">Bradysia difformis</Emphasis> (Sciaridae: Diptera) populations reflects movement of an invasive insect between forestry nurseries

The fungus gnat, Bradysia difformis (Sciaridae: Diptera) has recently been recorded for the first time from South Africa where it has been found in forestry nurseries. The presence of this insect in all the major forestry nurseries as the dominant and only sciarid species raises intriguing questions regarding its origin and population genetic structure. A 395 bp portion of the mitochondrial COI gene was analysed from B. difformis individuals collected from four nursery populations in South Africa and three nursery populations in Europe. Shared haplotypes between South African and European populations indicated a historical connection. South African populations showed high genetic diversity and low genetic differentiation. These patterns most likely reflect multiple and/or relatively large introductions of B. difformis into South Africa from its origin combined with subsequent and continued movement of plants between nurseries.