ApoFnr binds as a monomer to promoters regulating expression of enterotoxin genes of Bacillus cereus.

International audienceBacillus cereus Fnr is a member of the Crp/Fnr (cAMP-binding protein/fumarate nitrate reduction regulatory protein) family of helix-turn-helix transcriptional regulators. It is essential for the expression of Hbl and Nhe enterotoxin genes independently of the oxygen tension in the environment. We studied aerobic Fnr binding to target sites in promoters regulating the expression of enterotoxin genes. B. cereus Fnr was overexpressed and purified as either a C-terminal His-tagged (FnrHis) fusion protein or an N-terminal fusion protein tagged with the Strep-tag (IBA BioTAGnology) (StrepFnr). Both recombinant Fnr proteins were produced as apoforms (clusterless) and occured as mixtures of monomers and oligomers in solution. However, apoFnrHis was mainly monomeric, while apoStrepFnr was mainly oligomeric, suggesting that the His-tagged C-terminal extremity may interfere with oligomerization. The oligomeric state of apoStrepFnr was dithiothreitol sensitive, underlining the importance of a disulphide bridge for apoFnr oligomerization. Electrophoretic mobility shift assays showed that monomeric apoFnr, but not oligomeric apoFnr, bound to specific sequences located in the promoter regions of the enterotoxin regulators fnr, resDE and plcR and the structural genes hbl and nhe. The question of whether apoFnr binding is regulated in vivo by redox-dependent oligomerization is discussed

Suspended particulate matter distribution and composition on the northern Portuguese margin

On the North Atlantic continental margins, the Portuguese continental shelf has a singular morphology and hydrology. These characteristics are reflected in the sedimentary processes that occur on the continental shelf and in deeper areas. The main objective of the present paper is to review the nature, spatial distribution and dynamics of suspended particulate matter (SPM) on the continental shelf north of 41° N, in winter conditions. The data were collected during the Corrente da Vertente (CORVET) cruise sponsored by the Portuguese Hydrographic Institute in November 1996. During the cruise, hydrographic data (conductivity, temperature, and nephelometry) were obtained along transepts perpendicular to bathymetric contours. At most of these stations, suspended sediment samples were also collected from near-bottom turbid water (the bottom nepheloid layer, BNL) and from the surface turbid water (-5 m). SPM over the shelf consists of inorganic particles, skeletal biogenic particles and organic debris. Inorganic matter is dominated ( 60 %) by fine silt particles ( 15 μm) in the inner shelf near river mouths, although in the middle-to-outer shelf biogenic debris prevails in coarser particles (greater than 28 μm). Currents and waves induce resuspension events, which are clearly shown by concentration fluctuations in the BNL. These events are greatly intensified during storms. The nephelometrical distribution near the bottom can reflect this events with a rise of the values in the middle shelf far away from the river inputs. Near the continental slope, the BNL nourish the intermediate nepheloid layer (INL). The nourishment increases during storm events, showing the importance of these events to the transport of particles to deeper areas.La plataforma continental portuguesa, situada en el ámbito más vasto del margen continental del Atlántico norte, puede ser considerada como única a causa de sus características morfológicas e hidrológicas. Estas características se reflejan en los procesos sedimentarios que ocurren tanto en la plataforma continental como en las áreas más profundas. El objetivo principal de este trabajo es caracterizar el tipo, la distribución espacial y la dinámica de la materia particulada en suspensión de la plataforma continental situada al norte de 41° N, en condiciones invernales. Los datos fueron obtenidos en el mes de noviembre de 1996 durante la misión CORVET (Corrente da Vertente) promovida por el Instituto Hidrográfico de la Marina Portuguesa, según secciones perpendiculares a la costa. Las muestras de materia en suspensión fueron obtenidas a 5 m de la superficie y en cercanía del fondo. El análisis de las muestras indica que la materia particulada en suspensión de la plataforma continental está constituida esencialmente por partículas terrígenas, bioclastos siliciosos y calcáreos, así como de otros detritos orgánicos. Cerca de la desembocadura de los ríos, más del 60 % de la materia terrígena está compuesta de partículas finas ( 15 μm); en cambio, en el resto de la plataforma los bioclastos son dominantes y presentan, generalmente, dimensiones superiores ( 28 μm). Las corrientes y las olas inducen periodos de resuspensión de las partículas sedimentarias más finas localizadas en la plataforma media. Este fenómeno, ilustrado por las variaciones de concentración de la capa nefeloide de fondo, es particularmente intenso durante las tormentas, alimentando entonces una capa nefeloide intermediaria que circula cerca del borde de la plataforma. Los valores observados muestran la importancia de los periodos energéticos en el traslado de las partículas de la plataforma continental hacia los sectores más profundos.Instituto Español de Oceanografí

Anthropogenic influence in the Sado estuary (Portugal): a geochemical approach

Two areas of salt marsh in the Sado estuary – Faralhão, on the industrialized north margin and Malha da Costa, on the south bank, sheltered by a uninhabited sand spit – have been cored to study the geochemical signature of anthropogenic activity in recent (19th century onwards) intertidal sediments. Short cores were taken from each site from both the high and low marsh and were studied for texture, organic matter, pH, carbonates and geochemistry, including the heavy metals Cu, Pb and Zn. The marsh sediments are free of carbonate bioclasts and quite uniform in texture, consisting of acid to neutral clayey silt in addition to organic matter, which is higher in the top 20 cm. The vertical concentration profiles of heavy metals indicates enrichment in the top 30 cm of the sediment of the high marsh, in contrast with underlying high and low marsh sediment that has concentrations of metals at both studied sites similar to the Average Shale international reference/ continental crust sediments. The geochemical signal of anthropogenic influence in the marsh sediment was determined to have commenced from 1900-1920 using the sedimentation rates derived from 210Pb and 137Cs analyses. Spatial contrast in contamination levels was found within the estuary, with sediments of the Faralhão marsh showing higher enrichment factors of all metals. The anthropogenic increase of the supply of metal to the Sado estuary resulted from extensive exploitation of pyrite ore in the drainage basin until the1960’s; since that time, the sediments record a break in metal input, which resulted from a decline of the mining industry. However, in the marsh located closer to the industrial area (Faralhão) this break is followed by a local increase of heavy metal fluxes, which is interpreted as the result of intensification of anthropogenic influence. The comparison of metal concentrations in marsh sediments with target values established in quality guidelines indicates the studied area to be of environmental concern.Con el fin de estudiar el registro geoquímico de la actividad antrópica en sedimentos recientes (a partir del siglo XIX) e intermareales, han sido perforadas dos zonas de marisma en el Estuario del Sado- Faralhão, en el industrializado margen norte, y Malha da Costa, en la orilla sur, resguardada por una flecha litoral de arena no ocupada antrópicamente. Los pequeños sondeos realizados en cada punto de muestreo englobaron la marisma alta y baja. Fueron realizados análisis texturales, de contenido en materia orgánica, de pH, carbonatos y geoquímica, incluyendo los metales pesados Cu, Pb y Zn. Los sedimentos de marisma no muestran carbonato bioclástico y son bastante uniformes en la textura, consistiendo en limo arcilloso ácido a neutro junto con materia orgánica cuyo contenido es mayor en los 20 cm más superficiales. La concentración vertical de los perfiles de metales pesados indica un enriquecimiento en los 30 cm superficiales de la marisma alta, en contraste con los sedimentos subyacentes de marisma alta y baja que poseen concentraciones de metales similares a los referenciados internacionalmente para Average Shale / sedimentos de corteza continental. La señal geoquímica de la influencia antrópica en los sedimentos de marisma fue datada de 1900 a 1920 usando las tasas de sedimentación deducidas mediante 210Pb y 137Cs. Un contraste espacial en los niveles de contaminación fue encontrado en el interior del estuario: la marisma de Faralhão muestra valores con mayor enriquecimiento para todos los metales. El aporte antrópico de metales en el estuario de Sado resulta de la extensa explotación de pirita en la cuenca hasta 1960; a partir de ese momento los sedimentos registran una disminución en el aporte antropogénico de metales, consecuencia de la disminución del trabajo minero. Sin embargo, en la marisma cercana a la zona industrial (Faralhão) a esta interrupción le sigue un restablecimiento del flujo de metales pesados, interpretado como resultado del aumento de la influencia antrópica. La comparación de las concentraciones de metales en sedimentos de marisma con valores fijados establecidos en directrices de calidad sugiere una inquietud ambiental para el área de estudio

Characterization of a novel angular dioxygenase from fluorene-degrading Sphingomonas sp. strain LB126

In this study, the genes involved in the initial attack on fluorene by Sphingomonas sp. LB126 were investigated. The ? and ? subunits of a dioxygenase complex (FlnA1A2), showing 63% and 51% sequence identity respectively, with the subunits of an angular dioxygenase from Gram-positive Terrabacter sp. DBF63, were identified. When overexpressed in E. coli, FlnA1A2 was responsible for the angular oxidation of fluorene, fluorenol, fluorenone, dibenzofuran and dibenzo-p-dioxin. Moreover, FlnA1A2 was able to oxidize polycyclic aromatic hydrocarbons and heteroaromatics, some of which were not oxidized by the dioxygenase from Terrabacter sp. DBF63. Quantification of resulting oxidation products showed that fluorene and phenanthrene were preferred substrates

Late Holocene climatic oscillations traced by clay mineral assemblages and other palaeoceanographic proxies in Ria de Vigo (NW Spain)

This work aims to study recent climatic oscillations and their influence on sedimentation in the Ria de Vigo, a coastal embayment in Galicia, NW Spain. It is based on the study of clay mineral assemblages, in conjunction with other proxies (granulometric, geochemical, geochronological and microfaunal), in the core KSGX 24. A Benthic Foraminifera High Productivity (BFHP) proxy was used to determine changes in the flux of organic matter (OM) at the bottom of the study area. Total organic carbon (TOC) content is not a suitable proxy to estimate changes in the past supply of OM due to diagenetic processes.The sedimentation was finest in 3 sections: ~ 230–214 cm, ~ 185–73 cm and ~ 20–0 cm. These muddy sections are characterised, in general, by higher proportions of detrital minerals, concentrations of several chemical elements related to lithogenic sources and BFHP values. In addition, these sections are impoverished in carbonates, Ca, Sr and La when compared with the layers with the highest sand content.The clay mineral assemblage of the studied site, characterised by the dominance of illite, intermediate concentrations of kaolinite and minor amounts of smectite and chlorite, reveals the prevalence of a typical temperate humid climate in the last 3 ka BP, the estimated age for the core base. However, the quantities of illite and chlorite increase in the muddy layers. The characteristics of these muddy layers were interpreted as representing relatively cold climatic oscillations associated with the strengthening of northerly winds and the prevalence of an upwelling regime corresponding to wellknown periods, such as the first cold period of the Upper Holocene (~ 2.9 ka cal BP), the Dark Ages (between ~ 2.2 - 1.2 ka cal BP) and the Little Ice Age (~ 0.6 ka cal BP)