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Ndiaye M.L.,Cheikh Anta Diop University | Ndiaye M.L.,University of Geneva | Dieng Y.,Cheikh Anta Diop University | Niang S.,Cheikh Anta Diop University | And 4 more authors.
African Journal of Microbiology Research | Year: 2011

The aim of our survey was to assess the effect of irrigation water of the microbiological quality on the production chain of lettuce in the Dakar area. Microbiological analysis showed that 35% of irrigation water was contaminated by Salmonella spp. between the two water-types used for irrigation (groundwater and wastewater), no significant difference (p>0.05) in their degree of contamination was found. The incidence of different types of irrigation water on the contamination rate of lettuces from the farm (Pikine and Patte d'Oie) was not different either (p>0.05). However, the contamination rate of lettuce from markets of Dalifort and Grand-Yoff that were supplied by the area of Patte d'Oie was greater than those of Sham and Zinc supplied by Pikine (p<0.05). Comparison of serotypes of Salmonella isolated from irrigation water and lettuce showed that irrigation water may affect the microbiological quality of lettuce. Manures, frequently used as organic amendment in cultivating lettuce are another potential source of contamination. These results showed that lettuce may constitute effective vectors for the transmission of pathogens to consumers. Extensive treatment of the used wastewater and/or composting of manure could considerably reduce these risks. © 2011 Academic Journals.


Ndiaye M.L.,Laboratoire Of Traitement Des Eaux Use University | Ndiaye M.L.,University of Geneva | Niang S.,Laboratoire Of Traitement Des Eaux Use University | Pfeifer H.-R.,Center dAnalyse Minerale | And 4 more authors.
Irrigation and Drainage | Year: 2011

The aim of this survey is to assess the microbiological impact of irrigation water on lettuces produced on two urban agricultural sites and sold on markets; 6 and 7%, respectively, of lettuces coming from the sites of Pikine and Patte d'Oie were Salmonella spp. positive. Lettuces irrigated with shallow groundwater ("Céanes" water) were more contaminated (8% at both Pikine and Patte d'Oie sites) compared to those irrigated with wastewater (4% at Pikine) or well water (5% at Patte d'Oie). As for the lettuces in marketplaces, their contamination seems to depend on the type of treatment occurring before sale. Lettuces previously washed in the "Céanes" were more contaminated than those rinsed with tap water at the marketplace. Salmonella spp. have been isolated from all marketplaces. However, the rates of contamination in markets surrounding Patte d'Oie are higher (9 and 11% at Grand Yoff and Dalifort) than those surrounding Pikine (4 and 2% at Zinc and Sham) or Rufisque, the control (2%). Our results confirm that the reuse of wastewater in irrigation is an alternative to animal manure. Its risk of microbial contamination can be significantly reduced by washing the vegetables with tap water before they are sold. © 2010 John Wiley & Sons, Ltd.


Peduzzi S.,Alpine Biology Center Foundation | Storelli N.,Institute of Microbiology Canton Tessin | Storelli N.,University of Geneva | Welsh A.,Swedish University of Agricultural Sciences | And 5 more authors.
Systematic and Applied Microbiology | Year: 2012

Strain Cad16 T is a small-celled purple sulfur bacterium (PSB) isolated from the chemocline of crenogenic meromictic Lake Cadagno, Switzerland. Long term in situ observations showed that Cad16 T regularly grows in very compact clumps of cells in association with bacteria belonging to the genus Desulfocapsa in a cell-to-cell three dimensional structure. Previously assigned to the genus Lamprocystis, Cad16 T, was here reclassified and assigned to the genus Thiodictyon. Based on comparative 16S rRNA gene sequences analysis, isolate Cad16 T was closely related to Thiodictyon bacillosum DSM234 T and Thiodictyon elegans DSM232 T with sequence similarities of 99.2% and 98.9%, respectively. Moreover, matrix-assisted laser desorption/ionization time of flight mass spectrometry (MALDI-TOF MS) analysis separated Cad16 T from other PSB genera, Lamprocystis and Thiocystis. Major differences in cell morphology (oval-sphere compared to rod-shaped) and arrangement (no netlike cell aggregates), carotenoid group (presence of okenone instead of rhodopinal), chemolithotrophic growth as well as the ability to form syntrophic associations with a sulfate-reducing bacteria of the genus Desulfocapsa suggested a different species within the genus Thiodictyon.This isolate is therefore proposed and described as . Candidatus "Thiodictyon syntrophicum" sp. nov., a provisionally novel species within the genus . Thiodictyon. © 2012 Elsevier GmbH.


Wirth S.B.,ETH Zurich | Gilli A.,ETH Zurich | Niemann H.,University of Basel | Dahl T.W.,University of Southern Denmark | And 12 more authors.
Geochimica et Cosmochimica Acta | Year: 2013

Here, we present sedimentological, trace metal, and molecular evidence for tracking bottom water redox-state conditions during the past 12,500years in nowadays sulfidic and meromictic Lake Cadagno (Switzerland). A 10.5m long sediment core from the lake covering the Holocene period was investigated for concentration variations of the trace metals Mn and Mo (XRF core scanning and ICP-MS measurements), and for the presence of anoxygenic phototrophic sulfur bacteria (carotenoid pigment analysis and 16S rDNA real time PCR). Our trace metal analysis documents an oxic-intermediate-sulfidic redox-transition period beginning shortly after the lake formation ~12.5kyr ago. The oxic period is characterized by low sedimentary Mn and Mo concentrations, as well as by the absence of any remnants of anoxygenic phototrophic sulfur bacteria. Enhanced accumulation/preservation of Mn (up to 5.6wt%) in the sediments indicates an intermediate, Mn-enriched oxygenation state with fluctuating redox conditions during a ~2300-year long transition interval between ~12.1 and 9.8kyr BP. We propose that the high Mn concentrations are the result of enhanced Mn2+ leaching from the sediments during reducing conditions and subsequent rapid precipitation of Mn-(oxyhydr)oxide minerals during episodic and short-term water-column mixing events mainly due to flood-induced underflows. At 9800±130calyr BP, a rapid transition to fully sulfidic conditions is indicated by the marked enrichment of Mo in the sediments (up to 490ppm), accompanied by an abrupt drop in Mn concentrations and the increase of molecular biomarkers that indicate the presence of anoxygenic photosynthetic bacteria in the water column. Persistently high Mo concentrations >80ppm provide evidence that sulfidic conditions prevailed thereafter until modern times, without any lasting hypolimnetic ventilation and reoxygenation. Hence, Lake Cadagno with its persistently stable chemocline offers a framework to study in great temporal detail over ~12kyr the development of phototrophic sulfur bacteria communities and redox processes in a sulfidic environment, possibly depicting analogous conditions in an ancient ocean. Our study underscores the value of combining sedimentological, geochemical, and microbiological approaches to characterize paleo-environmental and -redox conditions in lacustrine and marine settings. © 2013 Elsevier Ltd.


Peduzzi S.,Cantonal Institute of Microbiology | Peduzzi S.,Alpine Biology Center Foundation | Welsh A.,Texas State University | Demarta A.,Cantonal Institute of Microbiology | And 4 more authors.
International Journal of Systematic and Evolutionary Microbiology | Year: 2011

Two isolates, designated CadH11 T and Cad448 T, representing uncultured purple sulfur bacterial populations H and 448, respectively, in the chemocline of Lake Cadagno, a crenogenic meromictic lake in Switzerland, were obtained using enrichment and isolation conditions that resembled those used for cultured members of the genus Thiocystis. Phenotypic, genotypic and phylogenetic analyses of these isolates confirmed their assignment to the genus Thiocystis. However, 16S rRNA gene sequence similarities of 98.2% between CadH11 T and Cad448 T, and similarities of 97.7 and 98.5 %, respectively, with their closest cultured relative Thiocystis gelatinosa DSM 215 T, as well as differences in DNA G+C content and carbon source utilization suggested that the isolates belonged to two distinct species. DNA-DNA hybridization of CadH11T and Cad448T with T. gelatinosa DSM 215 T showed relatedness values of 46.4 and 60.8 %, respectively; the relatedness value between CadH11 T and Cad448 T was 59.2 %. Based on this evidence, strains CadH11 T and Cad448 T represent two novel species within the genus Thiocystis, for which the names Thiocystis chemoclinalis sp. nov. and Thiocystis cadagnonensis sp. nov. are proposed, respectively. The type strains of T. chemoclinalis sp. nov. and T. cadagnonensis sp. nov. are CadH11 T (5JCM 15112 T 5KCTC 5954 T) and Cad448 T (5JCM 15111 T 5KCTC 15001 T), respectively. © 2011 IUMS.

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