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

Abstract

The localization, viability, and culturability of Pseudomonas fluorescens 92 rkG5 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 92 rkG5.

The rhizosphere: a playground and battlefield for soilborne pathogens and beneficial microorganisms

“…Advances in molecular techniques, fluorescence labeling, and imaging such as confocal laser microscopy, may be useful in the future. These techniques have been used to study colonization of roots by biocontrol bacteria and fungi (Gamalero et al 2005;Bloemberg et al 2000;Lu et al 2004) and infection of roots by Fusarium (Lagopodi et al 2002;Bolwerk et al 2005;Olivain et al 2006), but these have been descriptive and have not employed spatial statistics.…”

Plant growth-promoting bacteria in the rhizo- and endosphere of plants: Their role, colonization, mechanisms involved and prospects for utilization

“…For example, some rhizosphere-restricted bacteria as well as some endophytes have been detected on and/or inside plants as VBNC cells (Hurek et al, 2002;Gamalero et al, 2004Gamalero et al, , 2005, but it is currently unknown why cells switch to this state. Switching to a VBNC state on and inside plants might indicate that bacteria experience stress during host colonization, but this phenomenon is still poorly understood.…”

Transparent soil microcosms allow 3D spatial quantification of soil microbiological processesin vivo

“…High bacterial abundance was found on the root tips 11,[13][14][15] and at root branching zones. 13 Yet other studies reported an absence or scarcity of bacterial colonisation at the root tips [16][17][18][19][20] perhaps caused by the high turnover of mucilage and border cells at the root apex. 20 It is likely that the choice of the technique used to determine bacterial numbers along the root has a strong influence on bacterial count estimates.…”