Biologie

ENGLISH ABSTRACT (& RESUME FRANCAIS). Different aspects of vascular plants diversity have been studied in four sites of French Guyana rainforest. The analysis of structural and taxonomic diversity of each components of plant population was enabled by a life form classification of species and by the definition of biovolume and presence indices. Diversity distribution trends evidence invariable progression in species-area relationships within homogeneous vegetation units. This evenness is observed for each life form guild and in every study sites. This allows to propose a species diversity index, independent from sampling surface areas. This index shows higher diversity in terra firme primary forests, compared to secondary and swamp forests. A correlation between the number of woody climbers families and total species diversity is observed in the plot samples, providing a diversity indicator guild. A heterogeneity index was also determined in order to take into account the variety of differentiated vegetation units inside the forest continuum. Finally, the proportion of redundant taxa was estimated, giving rise to hypothetical evolutionary explanation for the intensity of speciation in tropical rainforests. The tools elaborated in this work can be used to delimit high species and habitat diversity areas. Complementary to qualitative floristical informations, biodiversity measurements may provide essential data for the management of biological forest resources and for the conservation of an invaluable natural heritage

RÉSUMÉ. Différents aspects de la diversité des plantes vasculaires ont été étudiés dans quatre sites de forêt tropicale de basse altitude en Guyane. Une classification des espèces par cortèges de formes et la définition d’indices de bio-volume et de présence ont permis d’analyser la structure et la diversité taxonomique de chaque composante du peuplement. Les modèles de distribution de la diversité spécifique font apparaître une progression invariable dans les relations aire-espèces dans des ensembles homogènes de végétation. Cette régularité a été observée pour chaque cortège et dans toutes les stations. Ceci permet de proposer un indice de diversité spécifique, indépendant de la superficie d’échantillonnage. Cet indice montre une diversité plus élevée dans les forêts primaires comparée aux forêts secondaires et marécageuses. La recherche de cortèges indicateurs a révélé une corrélation entre le nombre de familles de lianes ligneuses et la diversité spécifique totale des parcelles échantillonnées. Un indice d’hétérogénéité de l’habitat a également été défini afin de rendre compte de l’existence d’unités de végétation différenciées à l’intérieur du continuum forestier. Enfin, le degré de redondance taxonomique a été mesuré et comparé entre chaque site étudié, donnant lieu à des hypothèses permettant d’expliquer l’intensité de la spéciation en forêt tropicale. Les outils élaborés au cours de ce travail permettent de délimiter les zones où la diversité d’espèces et d’habitats est la plus grande. Complémentaire aux informations floristiques qualitatives, la quantification de la biodiversité peut fournir des informations essentielles pour la gestion des ressources biologiques et la conservation d’un patrimoine naturel inestimable.

Within the framework of a flora and vegetation study carried out in the Bakhuis Mountains in Suriname, South America, descriptors of plant species and habitat biodiversity were used to set local-scale botanical conservation priorities. Species' diversity and habitat heterogeneity indices, relative scarcity, fragility indices for habitats and ratios of species of concern, such as rare, endemic or subendemic taxa, were processed through a multi-criteria analysis to determine a conservation priority index. One of the main objectives of the study was the setting of defensible conservation priorities at a local and regional scale. Results are discussed, with a focus on land use planning and biodiversity conservation in one of the three major evergreen rainforest regions in the world. Among the 13 vegetation types described in the study perimeter, two that were restricted in area were considered to be of higher concern for wildlife conservation: meso-xeric dwarf thickets found on latero-bauxitic hardcap hilltops, with a distinctive floristic composition, and Buxus citrifolia mesic forest patches, described for the first time in Suriname.

Rôle des perturbations actuelles et passCes dans la dynamique et la mosaïque forestikre. Rev. Ecologie (Terre et Me), 50,209-22 RiCra, B., Philippe, M., Dosso. M., Bernard, R., Vidal-Majar, D. and Dechambre, M. (1994). Etude du Systeme sol-vtgetation en fôret tropicale guyanaise a l'aide d'observation radar en visCe verticale.

Bactris nancibaensis un palmier de sous-bois extrêmement rare, endémique du nord de la Guyane est une espèce intégralement protégée. Son aire de répartition particulièrement restreinte permet de la classer parmi les espèces prioritaires de premier rang de la flore guyanaise. La rédaction d'un Plan National d'Action pour sa conservation a été demandée par les services régionaux chargés de l'environnement afin de préparer l'organisation, dans les meilleures conditions, des mesures et actions permettant d'assurer sa conservation. Le document présenté ici rassemble les données relatives à cet objectif.

Rôle des perturbations actuelles et passCes dans la dynamique et la mosaïque forestikre. Rev. Ecologie (Terre et Me), 50,209-22 RiCra, B., Philippe, M., Dosso. M., Bernard, R., Vidal-Majar, D. and Dechambre, M. (1994). Etude du Systeme sol-vtgetation en fôret tropicale guyanaise a l'aide d'observation radar en visCe verticale.

Guyane s'est deroulee en trois etapes : 1) constitution d'une base de donnees informatisee regroupant le maximum d'informations sur les 5 210 especes de Ia !lore regionale ; 2) exploitation scientifique de Ia base de donnees et extraction de 700 especes d'interet patrimonial (plantes protegees par convention internationale, plantes rares, menacees, endemiques, plantes sauvages apparentees aux plantes cultivees et arbres d'interet particulier) ; 3) selection parrni ces especes et seton des criteres precis de rarete et de menaces de 83 taxons (soil 1,5% des especes guyanaises) meritant un statui officiel de protection. La lisle des plantes a proteger comprend essentiellement des plantes herbacees ou ligneuses de Ia region littorale, des collines auteur de Cayenne et des savanes et marais cotiers, c'est-a-dire les especes les mieux connues des sites les plus menacees.

(ABSTRACT IN ENGLISH) In the global context of strong demographic expansion, environmental deteriorations and biodiversity loss, the knowledge of French Guiana ecosystems and biological communities and especially of it’s flora and vegetations is an essential prerequisite to allow the sustainable management and conservation of an invaluable natural heritage.

RESUME - Dans un contexte de forte croissance démographique, de dégradation de l’environnement et de perte de biodiversité à l’échelle mondiale, la connaissance des écosystèmes et des communautés biologiques de Guyane, en particulier de sa flore et des végétations qui l’abrite, est un préalable incontournable pour permettre la gestion durable et la conservation d’un patrimoine naturel irremplaçable…

Initially, the effect of water activity (aw) on heat resistance of Bacillus cereus spores (decimal reduction time) was investigated. A linear relationship was found between log D and 1-aw. The combined effects of temperature (85-105°C), pH (4.5-6.5) and water activity (0.80-1) were then studied. A four parameter model was fitted to the data. This model appeared to be parsimonious with each parameter having a biological significance. Interactions between factors were observed but they accounted for <2.4% of the total variation and they were not taken into account by the model.

3 application of the Weibull frequency distribution model. 4 5 P. MAFART, O. COUVERT, S. GAILLARD and I. LEGUERINEL 6 7 ABSTRACT A simple and parsimonious model originated from the Weibull frequency 8 distribution was proposed to describe non linear survival curves of spores. This model 9 was suitable for downward concavity curves (Bacillus cereus and Bacillus pumilus) as 10 well as for upward concavity curves (Clostridium botulinum). It was shown that 11 traditional F-values calculated from this new model were no more additive, to such an 12 extend that a heat treatment should be better characterized by the obtained decade 13 reduction of spores. A modified Bigelow method was then proposed to assess this decade 14 reduction or to optimize the heat treatment for a target reduction ratio. 15 16 20 logarithm of the number of surviving microorganisms and the treatment time at a given 21 temperature is used to estimate the D-value (time of decimal reduction). However, in many 22 cases , the survival curve of heated microorganisms is not linear and present a downward 23 concavity (presence of a shoulder) or an upward concavity (presence of a tail). A number of 24 models describing non linear survival curves were proposed. Some of them are mechanistic or 25 42 Where N represents the number of surviving cells after a duration of heat treatment t, while 43 N 0 is the initial size of the alive population. For a given temperature, parameter distribution 44 are k and p. 45 Peleg and Cole (1998) wrote out this model in the following decimal logarithmic form: 65 and suspended in sterile distilled water and washed three times by centrifugation (10000xg for 66 15 min) (Bioblock Scientific, model Sigma 3K30). The pellet was then resuspended in 5 ml 67 distilled water and 5 ml ethanol. The obtained suspension was then kept at 4°C during 12 68 hours in order to eliminate vegetative non sporulated bacteria, and washed again three times 69 by centrifugation. 70 Lastly the final suspension (about 10 10 spores ml -1 ) was at last distributed in sterile Eppendorfs 71 microtubes and kept at 4°C.

The combined effects of temperature, pH and organic acids (lactic, acetic and propionic) on the growth kinetics of Listeria innocua ATCC 33090 were studied. First, a multiplicative model was built assuming independent effects of all environmental factors. Thus, the model was expanded by the inclusion of a novel term describing the effects of interactions on the growth/no growth limits. The proposed approach allows an accurate description of the boundary between growth and no growth of Listeria. D

After heat treatment, the temperature incubation and the medium composition, (pH and sodium chloride content) influence the capacity of injured spores to repair heat damage. The concept of heat resistance D-(decimal reduction time) and z-values (temperature increase which results in a ten fold reduction of the D value) is not sufficient and the ratio of spore recovery after incubation should be considered in calculations used in thermal processing of food. This paper aims to derive a model describing the recovery of injured spores as a function of both the heat treatment intensity and the environmental conditions. According to data from numerous investigators, when spores are incubated in unfavorable conditions, the ratio of cell recovery and the apparent D-value are reduced. Moreover the ratio of the apparent D-value and the estimated in optimal incubation D-value is constant and independent of the heat treatment conditions. Beyond these observations it is shown that the ratio of cell recovery with respect to the heat treatment F-value (exposure time, in minutes, at 121.18C which results in the same destruction ratio that the considered heat treatment does) is linear and can be quantified by using two factors independent of the heat treatment: the g-factor reflects the degree of precariousness due to the heat stress while the´-factor reflects more intrinsically the incubation conditions without previous heat treatment. The g-factor varies as a function of the incubation temperature according to an Arrhenius law. © 1997 Elsevier Science B. V. * medium both influence the ratio of cell recovery and Corresponding author. Tel: 11 33 2 98 100060; Fax: 11 33 2 98 100001 estimated heat resistance values. It is generally 0168-1605 / 97 / $17.00

The development of relationships between the pH of a heating medium and the thermal resistance of contaminant micro-organisms is important and of public health significance. A number of mathematical models have been presented in recent years, including that of ( ) Mafart and Leguerinel 1998 . However,

Leguérinel. Modelling the influence of palmitic, palmitoleic, stearic and oleic acids on apparent heat resistance of spores of Bacillus cereus NTCC 11145 and Clostridium sporogenes Pasteur 79.3. International Journal of Food Microbiology, Elsevier, 2010, pp.242-247. <hal-00654177> HAL Id: hal-00654177 http://hal.univ-brest.fr/hal-00654177 Modelling the influence of palmitic, palmitoleic, stearic and oleic acids on apparent heat 1 resistance of spores of Bacillus cereus NTCC 11145 and Clostridium Sporogenes Pasteur 2 79.3. 3 Abstract 15