Modulation of Metabolism and Switching to Biofilm Prevail over Exopolysaccharide Production in the Response of Rhizobium alamii to Cadmium

PLOS ONE, Nov 2011

Heavy metals such as cadmium (Cd2+) affect microbial metabolic processes. Consequently, bacteria adapt by adjusting their cellular machinery. We have investigated the dose-dependent growth effects of Cd2+ on Rhizobium alamii, an exopolysaccharide (EPS)-producing bacterium that forms a biofilm on plant roots. Adsorption isotherms show that the EPS of R. alamii binds cadmium in competition with calcium. A metabonomics approach based on ion cyclotron resonance Fourier transform mass spectrometry has showed that cadmium alters mainly the bacterial metabolism in pathways implying sugars, purine, phosphate, calcium signalling and cell respiration. We determined the influence of EPS on the bacterium response to cadmium, using a mutant of R. alamii impaired in EPS production (MSΔGT). Cadmium dose-dependent effects on the bacterial growth were not significantly different between the R. alamii wild type (wt) and MSΔGT strains. Although cadmium did not modify the quantity of EPS isolated from R. alamii, it triggered the formation of biofilm vs planktonic cells, both by R. alamii wt and by MSΔGT. Thus, it appears that cadmium toxicity could be managed by switching to a biofilm way of life, rather than producing EPS. We conclude that modulations of the bacterial metabolism and switching to biofilms prevails in the adaptation of R. alamii to cadmium. These results are original with regard to the conventional role attributed to EPS in a biofilm matrix, and the bacterial response to cadmium.

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Modulation of Metabolism and Switching to Biofilm Prevail over Exopolysaccharide Production in the Response of Rhizobium alamii to Cadmium

et al. (2011) Modulation of Metabolism and Switching to Biofilm Prevail over Exopolysaccharide Production in the Response of Rhizobium alamii to Cadmium. PLoS ONE 6(11): e26771. doi:10.1371/journal.pone.0026771 Modulation of Metabolism and Switching to Biofilm Prevail over Exopolysaccharide Production in the Response of Rhizobium alamii to Cadmium Mathieu Schue 0 1 Agnes Fekete 0 1 Philippe Ortet 0 1 Catherine Brutesco 0 1 Thierry Heulin 0 1 Philippe Schmitt-Kopplin 0 1 Wafa Achouak 0 1 Catherine Santaella 0 1 Paul Cobine, Auburn University, United States of America 0 a Current address: CNRS, UPR 9025, Lab Enzymologie Interfaciale et Physiologie de la Lipolyse , Marseille, France b Current address: CEA, DSV, IBEB , Laboratoire de Bioe nerge tique Cellulaire , Saint-Paul-lez-Durance , France 1 1 CEA, Lab Ecol Microbienne Rhizosphere & Environm Extre , iBEB, DSV, Saint-Paul-lez-Durance, France, 2 CNRS , Unite Mixte Rech Biol Vegetale & Microbiol Enviro, UMR 6191 , Saint-Paul-lez-Durance , France , 3 Universite Aix Marseille , Saint-Paul-lez-Durance , France , 4 Helmholtz-Zentrum Muenchen-German Research Center for Environmental Health, Institute for Ecological Chemistry, Department of BioGeochemistry and Analysis , Neuherberg, Germany , 5 Department for Chemical-Technical Analysis Research Center Weihenstephan for Brewing and Food Quality, Technische Universita t M u nchen , Freising-Weihenstephan , Germany Heavy metals such as cadmium (Cd2+) affect microbial metabolic processes. Consequently, bacteria adapt by adjusting their cellular machinery. We have investigated the dose-dependent growth effects of Cd2+ on Rhizobium alamii, an exopolysaccharide (EPS)-producing bacterium that forms a biofilm on plant roots. Adsorption isotherms show that the EPS of R. alamii binds cadmium in competition with calcium. A metabonomics approach based on ion cyclotron resonance Fourier transform mass spectrometry has showed that cadmium alters mainly the bacterial metabolism in pathways implying sugars, purine, phosphate, calcium signalling and cell respiration. We determined the influence of EPS on the bacterium response to cadmium, using a mutant of R. alamii impaired in EPS production (MSDGT). Cadmium dosedependent effects on the bacterial growth were not significantly different between the R. alamii wild type (wt) and MSDGT strains. Although cadmium did not modify the quantity of EPS isolated from R. alamii, it triggered the formation of biofilm vs planktonic cells, both by R. alamii wt and by MSDGT. Thus, it appears that cadmium toxicity could be managed by switching to a biofilm way of life, rather than producing EPS. We conclude that modulations of the bacterial metabolism and switching to biofilms prevails in the adaptation of R. alamii to cadmium. These results are original with regard to the conventional role attributed to EPS in a biofilm matrix, and the bacterial response to cadmium. - The exposure of bacterial cells to heavy metals in their environment mediates biological effects, usually through the direct or indirect action of reactive oxygen species [1,2]. In fact, nonredox-reactive metals, such as cadmium, show a high degree of reactivity towards sulfur, nitrogen and oxygen atoms in biomolecules. Cadmium may bind sulfur in essential enzymes, and alter their functions. Many studies have focused on the molecular mechanism of bacterial cell tolerance to cadmium, mainly for the case of species that are resistant to high metal concentrations, such as Stenotrophomonas [3] or Cupriavidus metallidurans (review in [4]). However, cadmium concentrations and its availability in metal contaminated soils are generally low. At low cadmium concentrations, Dedieu et al. [5] studied the interactions of Sinorhizobium meliloti extracellular compounds on cadmium speciation and availability, and Page`s et al. [6] reported on the completely different adaptation mechanisms of phenotypic variants of Pseudomonas brassicacearum in the presence of cadmium. Varied mechanisms account for cadmium detoxication in bacteria, involving exclusion, binding and sequestration. Cadmium is removed from cells by metal efflux transporters [7,8,9], reduced as cadmium sulfide [10], precipitated as insoluble salts [11], immobilized within the cell walls [12], or linked to chelating agents [13,14]. Cell exudates, such as proteins, siderophores and to a minor extent polysaccharide, play a role in the short-term interaction between Sinorhizobium meliloti and cadmium [5,15]. Because the adsorption of cadmium as well as of other metals can be associated with the secretion of exopolysaccharide (EPS) or capsular material [2,16,17], EPSs are considered as potential metal transporters in soil [18,19]. Gram-negative soil bacteria belonging to the commonly named rhizobia are able to produce EPSs with a large diversity of chemical structures [20,21]. These EPSs are the main contributors in legume-rhizobia interactions, leading to nodulation and nitrogen fixat (...truncated)


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Mathieu Schue, Agnes Fekete, Philippe Ortet, Catherine Brutesco, Thierry Heulin, Philippe Schmitt-Kopplin, Wafa Achouak, Catherine Santaella. Modulation of Metabolism and Switching to Biofilm Prevail over Exopolysaccharide Production in the Response of Rhizobium alamii to Cadmium, PLOS ONE, 2011, Volume 6, Issue 11, DOI: 10.1371/journal.pone.0026771