Article

Microbial Ecology

, Volume 50, Issue 2, pp 289-297

Colonization of Tomato Root Seedling by Pseudomonas fluorescens 92rkG5: Spatio–temporal Dynamics, Localization, Organization, Viability, and Culturability

  • Elisa GamaleroAffiliated withDipartimento di Scienze dell'Ambiente e della Vita, Università del Piemonte Orientale “Amedeo Avogadro” Email author 
  • , Guido LinguaAffiliated withDipartimento di Scienze dell'Ambiente e della Vita, Università del Piemonte Orientale “Amedeo Avogadro”
  • , Riccardo TomboliniAffiliated withSezione di Microbiologia Applicata, Dipartimento di Scienze e Tecnologie Biomediche, Università di Cagliari
  • , Lorena AvidanoAffiliated withDipartimento di Scienze dell'Ambiente e della Vita, Università del Piemonte Orientale “Amedeo Avogadro”
  • , Barbara PivatoAffiliated withDipartimento di Scienze dell'Ambiente e della Vita, Università del Piemonte Orientale “Amedeo Avogadro”
  • , Graziella BertaAffiliated withDipartimento di Scienze dell'Ambiente e della Vita, Università del Piemonte Orientale “Amedeo Avogadro”

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Abstract

The localization, viability, and culturability of Pseudomonas fluorescens 92rkG5 were analyzed on three morphological root zones (root tip + elongation, root hair, and collar) of 3-, 5-, and 7-day-old tomato plants. Qualitative information about the localization and viability was collected by confocal laser scanning microscopy. Quantitative data concerning the distribution, viability, and culturability were obtained through combined dilution plating and flow cytometry. Colonization by P. fluorescens affected root development in a complex way, causing a general increase in the length of the collar and early stimulation of the primary root growth (3rd day), followed by a reduction in length (7th day). The three root zones showed different distribution, organization, and viability of the bacterial cells, but the distribution pattern within each zone did not change with time. Root tips were always devoid of bacteria, whereas with increasing distance from the apex, microcolonies or strings of cells became more and more prominent. Viability was high in the elongation zone, but it declined in the older parts of the roots. The so-called viable but not culturable cells were observed on the root, and their proportion in the distal (root tip + elongation) zone dramatically increased with time. These results suggest the existence of a specific temporal and spatial pattern of root colonization, related to cell viability and culturability, expressed by the plant-beneficial strain P. fluorescens 92rkG5.