Whole-cell spectroscopy is a convenient tool to assist molecular identification of cultivatable marine bacteria and to investigate their adaptive metabolism |
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Authors: | Stéphanie Salaün Nelly Kervarec Dominique Haras Stéphane La Barre |
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Institution: | a Université Pierre et Marie Curie-Paris 6, UMR 7139 Végétaux marins et Biomolécules, Station Biologique F-29682, Roscoff, France b CNRS, UMR 7139 Végétaux marins et Biomolécules, Station Biologique F-29682, Roscoff, France c Université de Bretagne-Sud, Laboratoire de Biotechnologie et de Chimie Marines, EA3884, BP 92116, 5632 Lorient, France d Service Commun de Résonance Magnétique Nucléaire, Université de Bretagne Occidentale, UFR Sciences et Techniques, 6 avenue Le Gorgeu, BP 809 29285, Brest, France e Institut de Chimie, FRE 2446, 4 rue Blaise Pascal, Université Louis Pasteur, 67084 Strasbourg, France |
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Abstract: | Recent developments in whole-cell spectroscopic methods allow rapid characterization of microorganisms of interest to human health, but have yet to be widely applied to marine microbiological studies. In this study of bacteria associated with the kelp Laminaria digitata, we have isolated 18 epiphytic bacterial strains from several thalli, sequenced their 16S rDNA, built corresponding phylogenetic trees, and characterized them using spectroscopic methods. Molecular taxonomy revealed Gram+Actinobacteria and Gram−Alphaproteobacteria, Gammaproteobacteria and Bacteroidetes. Twelve marine reference strains (Gram+Firmicutes, and Gram−Alphaproteobacteria, Gammaproteobacteria and Bacteroidetes) were treated accordingly. Whole-cell MALDI-TOF MS spectral profiles of 29 of the 30 strains were built into a database against which 16 replicate spectra of each strain were compared and categorized into groups. The proton HR-MAS NMR stack plots allowed visual delineation into taxonomic groups according to their most common peaks, in agreement with identifiable compounds from corresponding D2O solution spectra. With both methods, these groups corresponded to taxa identified by 16S rDNA sequences, MALDI-TOF MS being more discriminative than HR-MAS NMR. Culture age did not influence the spectral signatures in both approaches. Most cells grown under minimal conditions (VNSS medium) afforded HR-MAS NMR profiles markedly different to those grown in enriched conditions (ZoBell medium), indicating different adaptive metabolic responses between the two media. Spectral signatures obtained under strictly controlled conditions can be used as rapid and reliable tools for taxonomic purposes and as markers of physiological status. |
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Keywords: | Marine bacteria MALDI-TOF MS HR-MAS NMR 16S rDNA taxonomy Physiological adaptation Brown algae |
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