Distribution of phytoplankton pigments in nine European estuaries and implications for an estuarine typology

Phytoplankton pigments were studied by LiquidChromatography (HPLC) in nine West Europeanestuaries. Three estuaries, i.e. the Rhine,Scheldt and the Gironde were sampled four timesto cover the different seasons, whereas theother six estuaries were sampled once. Pigmentdistributions in estuaries reflect bothriverine inputs as well as autochthonousblooms. Fucoxanthin was the most commonaccessory photosynthetic pigment showing thatDiatoms were the most common group in thestudied estuaries and were particularlydominant during autumn and winter. In the veryturbid Gironde estuary, degradation processeswere predominant between salinities 1 and 20,while Diatoms, Dinoflagellates and Cryptophytesbloomed above 20 salinity during spring andsummer. This contrasted with the highlyeutrophic but less turbid Scheldt, wherephytoplanktonic blooms occurred at lowsalinities close to the city of Antwerp. In theScheldt, we observed both a tenfold fluctuationof phytoplankton biomass and a fluctuatingpigment diversity index. In contrast,chlorophyll a was always low in theGironde, but we observed large variations ofpigment diversity among samplings duringdifferent seasons. Distribution of pheopigmentsshowed that the maximum turbidity zone (MTZ)was a highly reactive region for heterotrophicphytoplankton degradation. The Scheldt and theThames were the most anthropogenic influencedestuaries contrasting with the Gironde estuarythat has a less urbanised watershed. Anestuarine typology is proposed based on threeclusters emerging from a correspondenceanalysis of pigment variables and variablescharacterising the anthropogenic impact andphysical forcing.     

Contributions of the response regulators Ssk1p and Skn7p in the pseudohyphal development, stress adaptation, and drug sensitivity of the opportunistic yeast Candida lusitaniae

We recently characterized the histidine kinase receptor genes of Candida lusitaniae. For the present study, we have further investigated the role of SSK1 and SKN7, encoding response regulators. The results of functional analysis of mutants indicated that Ssk1p is involved in osmotolerance and pseudohyphal development, whereas Skn7p appears crucial for oxidative stress adaptation.     

Insight into the role of HOG pathway components Ssk2p, Pbs2p, and Hog1p in the opportunistic yeast Candida lusitaniae

In the present study, we have investigated the role of SSK2, PBS2, and HOG1, encoding modules of the high-osmolarity-glycerol mitogen-activated protein kinase pathway in Candida lusitaniae. Functional analysis of mutants indicated that Ssk2p, Pbs2p, and Hog1p are involved in osmotolerance, drug sensitivity, and heavy metal tolerance but not in oxidant stress adaptation.     

Glycerol induces reuterin production and decreases Escherichia coli population in an in vitro model of colonic fermentation with immobilized human feces

Lactobacillus reuteri ATCC 55730 is a probiotic strain that produces, in the presence of glycerol, reuterin, a broad-spectrum antimicrobial substance. This strain has been shown to prevent intestinal infections in vivo; however, its mechanisms of action, and more specifically whether reuterin production occurs within the intestinal tract, are not known. In this study, the effects of L. reuteri ATCC 55730 on intestinal microbiota and its capacity to secrete reuterin from glycerol in a novel in vitro colonic fermentation model were tested. Two reactors were inoculated with adult immobilized fecal microbiota and the effects of daily addition of L. reuteri into one of the reactors (c.10(8) CFU mL(-1)) without or with glycerol were tested on major bacterial populations and compared with addition of glycerol or reuterin alone. The addition of glycerol alone or with L. reuteri increased numbers of the Lactobacillus-Enterococcus group and decreased Escherichia coli. The addition of reuterin significantly and selectively decreased E. coli without affecting other bacterial populations. The observed decrease in E. coli concentration during the addition of glycerol (in presence or absence of L. reuteri) could be due to in situ reuterin production because 1,3-propanediol, a typical product of glycerol fermentation, was detected during the addition of glycerol.     

Single-nucleotide primer extension assay for detection and sequence typing of "Dehalococcoides" spp

A single-nucleotide primer extension (SNuPE) assay in combination with taxon-specific 16S rRNA gene PCR analysis was developed for the detection and typing of populations of the genus "Dehalococcoides". The specificity of the assay was evaluated with 16S rRNA gene sequences obtained from an isolate and an environmental sample representing two Dehalococcoides subgroups, i.e., the Cornell and the Pinellas subgroups. Only one sequence type, belonging to the Pinellas subgroup, was detected in a Bitterfeld-Wolfen region aquifer containing chlorinated ethenes as the main contaminants. The three-primer hybridization assay thus provided a fast and easy-to-implement method for confirming the specificity of taxon-specific PCR and allowed rapid additional taxonomic classification into subgroups. This study demonstrates the great potential of SNuPE as a novel approach for rapid parallel detection of microorganisms and typing of different nucleic acid signature sequences from environmental samples.     

Defensive adaptations of Thuja plicata to ungulate browsing: a comparative study between mainland and island populations

Forests on the Haida Gwaii (HG) archipelago (British Columbia, Canada) evolved for about 10,000 years in the absence of large-mammal browsing. The introduction of black-tailed deer (Odocoileus hemionus sitkensis) from the mainland prior to 1901 provides an opportunity to evaluate changes in the adaptive defensive responses of plants to herbivory. We compared (1) food choice by deer and (2) chemical defence (terpene concentrations) between HG and mainland red cedars (Thuja plicata) using (1) nursery-grown seedlings never exposed to deer, (2) branches from trees that grew before the introduction of deer ("old trees") and (3) saplings exposed to deer herbivory on the mainland and on HG. We used the first two plant categories to test the hypothesis that plants that evolve under low herbivory levels have lower anti-herbivore defences. We used saplings to study the consequences of the dramatic increase in browsing on HG. During food experiments, deer preferred HG seedlings and old tree branches compared to those from the mainland. Total monoterpene concentrations were much higher than diterpene concentrations in all plant categories. Within plant categories, multivariate analysis showed that terpene profiles differed significantly between HG and mainland red cedars: HG seedlings and old trees had lower monoterpene levels. These results suggest that some monoterpenes may be determinants of deer food choice and that the defences of HG plants are less effective than those of mainland plants. The deer used branches from HG and mainland saplings indiscriminately. However, terpene profiles differed significantly between HG and mainland saplings, with multivariate analysis suggesting a higher defensive response in browsed HG saplings. Monoterpene profiles were different in lightly and heavily browsed saplings from HG, suggesting that under the current browsing regime, individuals with the greatest constitutive defences, or with greatest potential for induced defences, grow better and are selected on HG.     

Differential regulation of gelatinase A and B and TIMP-1 and -2 by TNFalpha and HIV virions in astrocytes

Changes in the fine balance between matrix metalloproteinases and their tissue inhibitors, which drives extracellular matrix turnover, may be critical to central nervous system inflammation in HIV infection as well as in neurotoxicity. Although they do not produce virus when infected by HIV, astrocytes may be directly affected by the virion, because some viral proteins are known to transduce signaling in brain cells and are also sensitive to the major proinflammatory cytokine TNFalpha. We therefore studied the effects of HIV and TNFalpha on MMP-2, MMP-9 and their inhibitors, TIMP-1 and TIMP-2, in astrocytes, by zymography and ELISA, respectively, or by RT-PCR for both of them. HIV slightly increased the production of pro-MMP-2 and pro-MMP-9 by astrocytes, in a dose-dependent manner. TNFalpha strongly induced pro-MMP-9. TIMP-1 and TIMP-2 levels were affected only slightly, if at all, by HIV and TNFalpha. Thus, astrocyte/HIV contact may lead to extracellular matrix activation, which may be strongly amplified by the inflammatory response. Our data strongly suggest that, besides their physiological production of MMP-2, astrocytes would be a major source of MMP-9 in the inflamed brain.     

Bilirubin oxidase‐like proteins from Podospora anserina: promising thermostable enzymes for application in transformation of plant biomass

Plant biomass degradation by fungi is a critical step for production of biofuels, and laccases are common ligninolytic enzymes envisioned for ligninolysis. Bilirubin oxidases (BODs)‐like are related to laccases, but their roles during lignocellulose degradation have not yet been fully investigated. The two BODs of the ascomycete fungus Podospora anserina were characterized by targeted gene deletions. Enzymatic assay revealed that the bod1^Δ and bod2^Δ mutants lost partly a thermostable laccase activity. A triple mutant inactivated for bod1, bod2 and mco, a previously investigated multicopper oxidase gene distantly related to laccases, had no thermostable laccase activity. The pattern of fruiting body production in the bod1^Δbod2^Δ double mutant was changed. The bod1^Δ and bod2^Δ mutants were reduced in their ability to grow on ligneous and cellulosic materials. Furthermore, bod1^Δ and bod2^Δ mutants were defective towards resistance to phenolic substrates and H₂O₂, which may also impact lignocellulose breakdown. Double and triple mutants were more affected than single mutants, evidencing redundancy of function among BODs and mco. Overall, the data show that bod1, bod2 and mco code for non‐canonical thermostable laccases that participate in the degradation of lignocellulose. Thanks to their thermal stability, these enzymes may be more promising candidate for biotechnological application than canonical laccases.     

Particulate organic carbon in the estuarine turbidity maxima of the Gironde,Loire and Seine estuaries: origin and lability

A study of the particulate organic carbon (POC) in the estuarine turbidity maxima (ETMs) of the three major French macrotidal estuaries shows that the average contents are 1.5, 3.3 and 3.1% (expressed in % of dry suspended sediment) in the Gironde, Loire and Seine Estuaries, respectively. There is no seasonal variation of POC contents in the Gironde Estuary, whereas, they often increase in the Loire and the Seine Estuaries in spring and summer. The lability of the estuarine particulate organic matter was estimated by two analyses: 1/labile organic matter was measured as the organic carbon loss during incubation tests over one month; 2/ the hydrolysable organic fraction was determined after 6N HCl digestion. The organic fractions of the ETMs are mainly refractory. Any increase in the amount of POC as compared to the background levels (cited above) is always correlated to an increase of organic matter lability. The yearly average fluvial contributions by various particulate organic pools (soil and litter organic matter; organic matter of phytoplanktonic and human origin) that enter the three estuaries were quantified. In the Garonne River, soil and litter are the major (90%) POC sources. In the Loire system, due to the eutrophication of the river water, phytoplankton contributes up to 50% of the total POC load. In the Seine river, soil and litter contribute 70% of the total POC input; POC of human origin is also significant (10%), due to the impact of the City of Paris (10 million inhabitants). The lability of the different types of organic matter ranks as follows: phytoplankton ∼litter > human-origin organic matter >> soil. By combining the POC budgets and the lability of each type of organic fraction, it was possible to explain why the POC of the three ETMs is different and characterizes its refractory vs. labile nature.