Relative growth rate correlates negatively with pathogen resistance in radish: the role of plant chemistry

Plant growth rate has frequently been associated with herbivore defence: a large investment in quantitative defence compounds occurs at the expense of growth. We tested whether such a relationship also holds for growth rate and pathogen resistance. For 15 radish (Raphanus sativus L.) cultivars, we determined the potential growth rate and the resistance to fungal wilt disease caused by Fusarium oxysporum. We subsequently aimed to explain a putative negative relationship between growth rate and resistance based on plant chemical composition. Both growth rate and resistance level varied greatly among cultivars. Moreover, there was a strong negative correlation between growth rate and resistance, i.e. there are costs associated with a high resistance level. Roots of slow-growing, resistant cultivars have a higher biomass density. Using pyrolysis mass spectrometry. we part1y explained variation in both growth rate and resistance in terms of the same change in chemical composition. Leaves of slow-growing, resistant cultivars contained more cell wall material. Surprisingly, roots of slow-growing, highly resistant cultivars contained significantly less cell wall material, and more cytoplasmic elements (proteins). We speculate that this higher protein concentration is related to high construction and turn-over costs and high metabolic activity. The latter in turn is thought to be responsible for a rapid and adequate resistance reaction, in which phenols may be involved.     

Emerging role of ferrous iron in bacterial growth and host–pathogen interaction: New tools for chemical (micro)biology and antibacterial therapy

Chemical tools capable of detecting ferrous iron with oxidation-state specificity have only recently become available. Coincident with this development in chemical biology has been increased study and appreciation for the importance of ferrous iron during infection and more generally in host–pathogen interaction. Some of the recent findings are surprising and challenge long-standing assumptions about bacterial iron homeostasis and the innate immune response to infection. Here, we review these recent developments and their implications for antibacterial therapy.     

Survival of Escherichia coli in the environment: fundamental and public health aspects

In this review, our current understanding of the species Escherichia coli and its persistence in the open environment is examined. E. coli consists of six different subgroups, which are separable by genomic analyses. Strains within each subgroup occupy various ecological niches, and can be broadly characterized by either commensalistic or different pathogenic behaviour. In relevant cases, genomic islands can be pinpointed that underpin the behaviour. Thus, genomic islands of, on the one hand, broad environmental significance, and, on the other hand, virulence, are highlighted in the context of E. coli survival in its niches. A focus is further placed on experimental studies on the survival of the different types of E. coli in soil, manure and water. Overall, the data suggest that E. coli can persist, for varying periods of time, in such terrestrial and aquatic habitats. In particular, the considerable persistence of the pathogenic E. coli O157:H7 is of importance, as its acid tolerance may be expected to confer a fitness asset in the more acidic environments. In this context, the extent to which E. coli interacts with its human/animal host and the organism''s survivability in natural environments are compared. In addition, the effect of the diversity and community structure of the indigenous microbiota on the fate of invading E. coli populations in the open environment is discussed. Such a relationship is of importance to our knowledge of both public and environmental health.     

Comparison of peptidase activities in some fungi pathogenic to arthropods

Peptidases, highly specific toward several synthetic chromogenic peptides, were found in the mycelia of four arthropod pathogenic fungi: Aphanomyces astaci, Beauveria bassiana, Metarrhizium anisopliae, and Paecilomyces farinosus. A. astaci peptidases had high hydrolyzing activities toward most of the peptides, especially those with arginine in the P1 position, while those of B. bassiana and P. farinosus readily hydrolyzed peptides with valine and arginine, as well as proline and tyrosine in the P2 and P1 positions, respectively. The hydrolyzing capacities of M. anisopliae peptidases were similar to A. astaci, but showed lower specific activities. Casein or azocoll was only hydrolyzed by A. astaci peptidases. B. bassiana and M. anisopliae had a very low hydrolyzing capacity toward casein and could not degrade azocoll. P. farinosus had no hydrolyzing activity toward casein or azocoll. Only peptidases from the crayfish pathogen A. astaci could degrade the crayfish cuticle. The peptidase preparations of A. astaci and B. bassiana hydrolyzing MeO-Suc-Arg-Pro-Tyr-pNA or Bz-Phe-Val-Arg-pNA were of the serine type. The possible importance of peptidase activity of arthropod pathogenic fungi in the infection process is discussed.     

Keratinolytic and keratinophilic fungi of children's sandpits in the city of Turin

Soils rich in keratinic residues constitute a permanent or occasional reservoir for dermatophytes and keratinolytic and keratinophilic fungi, and are a source of potential infection for man and animals.The keratinolytic and keratinophilic mycoflora of 28 sandpits in Turin was studied to evaluate the risk of fungal skin infections that is run by children as they play in public parks and to lay the ground-work for a next epidemiological study of soil- and animal-inhabiting dermatophytes found in cities, and their impact on human dermatophytoses. Fifty seven species were isolated and a high percentage (52%) showed keratinolytic activity. Species of Microsporum, Trichophyton, Mariannaea, Aphanoascus, Chrysosporium, Malbranchea and Geomyces showed the most active keratinolysis.Work n. 315 performed under the auspices of the Centro di Studio sulla Micologia del Terreno del C.N.R. at the Dipartimento di Biologia vegetale dell Università di Torino.     

Leaf thionins, a novel class of putative defence factors

Leaf thionins of barley have been identified as a novel class of highly abundant polypeptides with antifungal activity, which are present in walls and vacuoles of barley leaf cells. Similar thionins occur not only in monocotyledonous but also in various dicotyledonous plants. The leaf thionins of barley are encoded by a complex multigene family, which consists of at least 50–100 members per haploid genome. The toxicity of these thionins for plant pathogenic fungi and the fact that their synthesis can also be triggered by pathogens strongly suggest that leaf thionins are involved in the mechanism of plant defence against microbiol infection.     

Cryptococcosis as an opportunistic infection in immunodeficiency secondary to paracoccidioidomycosis

We describe the case reports of two patients with immunodeficiency secondary to paracoccidioidomycosis (PCM) and opportunistic Cryptococcus neoformans infections. Secondary immunodeficiency likely occurred as a consequence of the intestinal loss of proteins and lymphocytes associated with malabsorption syndrome due to obstructed lymphatic drainage. Both patients had had severe abdominal involvement during the acute PCM disease. Immunological evaluation showed cellular and humoral immunity impairment. Cryptococcosis manifested as relatively well circumscribed lesions: osteolytic lesions of the skull in one patient, and pulmonary nodules in the other. The latter was treated surgically and with amphotericin B, whereas the other was treated with the combination amphotericin-B and flucytosine. Both patients had a good response to treatment with complete regression of the lesions. They have now 2 and 4 years of follow-up with maintenance therapy and no indication of reactivation of the infection. PCM also did not reactivate. The clinical and immunological characteristics of these patients are discussed and compared to the opportunistic C. neoformans infections of AIDS and transplant patients.     

Fusarium solani invader of the eggs of the insectPanstrongylus geniculatus in a vivarium

A strain ofFusarium solani sensu Snyder & Hansen invaded the eggs of the insectPanstrongylus geniculatus in a vivarium. None of the invaded eggs hatched. To establish experimentally the pathogenicity of thisFusarium species against the eggs ofP. geniculatus, the fungus and the eggs were incubated together under different relative humidities and temperatures. At 64% relative humidity and 26 °C, the fungus grew well colonizing and penetrating all of the chorions.Three embryos died and were also colonized byF. solani. Only 4 nymphs hatched and survived to day 20. It is concluded that the isolate ofF. solani was capable of colonizing and invading the chorion of the eggs under certain humidity and temperature conditions and cause the death of the embryos.