Mycobacterium ulcerans is the causative agent of Buruli ulcer, one of the most common mycobacterial diseases of humans. Recent studies have implicated aquatic insects in the transmission of this pathogen, but the contributions of other elements of the environment remain largely unknown. We report here that crude extracts from two green algae added to the BACTEC 7H12B culture medium halved the doubling time of M. ulcerans and promoted biofilm formation. Using the 7H12B medium, modified by the addition of the algal extract, and immunomagnetic separation, we also demonstrate that M. ulcerans is associated with aquatic plants in an area of the Ivory Coast where Buruli ulcer is endemic. Genotype analysis showed that plant-associated M. ulcerans had the same profile as isolates recovered in the same region from both aquatic insects and clinical specimens. These observations implicate aquatic plants as a reservoir of M. ulcerans and add a new potential link in the chain of transmission of M. ulcerans to humans.Mycobacterium ulcerans is an emerging environmental pathogen (2). It is the etiologic agent of Buruli ulcer, a necrotic skin disease highly prevalent in many countries throughout west Africa and one of the most common mycobacterial diseases in humans after tuberculosis and leprosy (2). M. ulcerans is the only mycobacterium known to produce a toxin, a polyketide-derived macrolide called mycolactone (10, 11). The infection begins with a painless nodule or papule that spreads over the surrounding tissue. Ischemic and necrotized tissue disappears and is replaced by centralized ulceration of the limb. At present, the only effective treatment consists of excision of the lesions, and this is often followed by extensive skin grafting (6).Until very recently M. ulcerans had never been isolated in culture from the environment. Indirect evidence from epidemiological studies suggests that M. ulcerans is an environmental mycobacterium present in swampy areas. Humans are thought to be infected through minor wounds or skin abrasions via contact with mycobacterium-containing water (33). In a previous study we demonstrated that aquatic insects are a possible mode of transmission of M. ulcerans to humans. We showed that, in an experimental mouse model, aquatic insects (Naucoridae) were able to transmit an infection by biting, thereby inoculating bacilli that had accumulated in the salivary glands of the insects (16). We were then able to isolate in pure culture M. ulcerans from the salivary glands of Naucoridae captured in a region of endemicity in the Ivory Coast. However it seems unlikely that these insects are the only environmental source of M. ulcerans. In another recent study, data gathered using an M. ulcerans-specific PCR to survey environments of endemicity in southeastern Australia identified aquatic plants as a possible reservoir of this pathogen (30).In this report, we test the hypothesis that M. ulcerans is associated with aquatic plants by studying the effects of crude aquatic plant extracts on the growth of M. ulcer...

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Une littérature abondante traite des difficultés de régénération naturelle des forêts d'Épicéa commun (

Abstract. The dynamics of Vaccinium myrtillus (bilberry) patches were studied in spruce (Picea abies) forest at the higher montane and lower subalpine level in the Tarentaise valley (Savoy, France). Although aerial parts of the shrub may give some indication of age and density of the patches, the annual growth and death of rhizomes are better indicators of patch dynamics. In some cases, dead and young rhizomes may occur simultaneously in the same patch, indicating that growth and death proceed continuously on the inside of dense patches. At mountain sites, slope position of plants significantly influences rhizome growth. A theoretical model of growth of bilberry patches is proposed which takes into account the anisotropic influenceof slope and the postulated independence of different rhizome units belonging to the same individual.

Morphologica1 features of twelve humus profiles demonstrating the diversity of vegetation types present in subalpine forests were compared, together with soil fauna. Two forest stands of spruce [Picea abies (L.) Karst.] in association with bilberry (Vaccinium myrtillus L.), located at 1630 and 1880 m altitude (Mâcot-La Plagne, Tarentaise valley, Savoy, France), were studied. Morphological observations of small soil volumes were made on disturbed samples by the method of Ponge, but here transformed into quantitative data. Analysis of the data gave evidence of a large degree of heterogeneity of the form of humus in a given forest stand, but most of the observed variation might be exp1ained by differences in vegetation, due to phases of the forest cycle and sylvicultural practices. Regeneration sites are characterized by the development of a herbaceous coyer under which a mull humus is built through the activity of burrowing earthworm species. During the phase of intense growth of spruce organic matter accumulates in the top few centimeters. At this stage, the Al horizon previously formed under the action of endogeous earthworms becomes inactive but its crumby structure remains stable.Anecic worms (earthworms with a high amplitude of vertical movements) appear again under adult trees. As a result, changes in the form of humus are observed, with seemingly mull formation (burying of litter) but without true incorporation of organic matter to mineral matter. This humus was named dysmull. Thus soil conditions that prevail in the regeneration sites were developed to some extent under pre-existing adult trees. A parallel the Macot-La Plagne commune, and belong to the same communal forest. The sites were studied for several years by the