Dynamic of the genetic structure of bacterial and fungal communities at different developmental stages of Medicago truncatula Gaertn. cv. Jemalong line J5

Abstract

Summary• The genetic structure of bacterial and fungal communities was characterized in the rhizosphere of Medicago truncatula Gaertn. cv. Jemalong line J5 at five developmental stages (three vegetative and two reproductive stages), and in three compartments (bulk soil, rhizosphere soil and root tissues).• The genetic structure of microbial communities was determined by cultivationindependent methods using directly extracted DNA that was characterized by automated ribosomal intergenic spacer analysis (ARISA).• Principal component analyses (PCA) indicate that, for all developmental stages, the genetic structure of microbial communities differed significantly by compartment, with a major shift in the community in root tissues corresponding to the most intimate compartment with the plant.• Differences were also recorded during plant development, the most significant being observed during the transition between vegetative and reproductive stages. Throughout this period, plants were shown to establish the highest level of symbiotic association (mycorrhization, nodulation) with arbuscular mycorrhizal fungi and Rhizobia. During the reproductive stages, the dynamics of the genetic structure differed between bacterial and fungal communities. At the last reproductive stage, the genetic structure of bacterial communities became close to that recorded during the first vegetative stages, suggesting a resilience phenomenon, whereas the genetic structure of fungal communities remained different from the vegetative stages and also from the early reproductive stages, suggesting a persistence of the rhizosphere effect.

Identification of Bacterial Groups Preferentially Associated with Mycorrhizal Roots of Medicago truncatula

“…These data are in agreement with our previous work (24) and underline the gradient of the rhizosphere effect.…”

“…1). A-RISA DNA fingerprinting was previously shown to be sensitive and robust enough to detect spatiotemporal changes in the genetic structures of the bacterial communities in the rhizosphere of M. truncatula (24).…”

“…In contrast to previous studies (5,19), our strategy avoided the inoculation of AM fungal isolates and allowed taking into account the diversity of Table 1). The genetic structures of bacterial communities were assessed by A-RISA DNA fingerprinting (24) in the two corresponding bulk soils and in the rhizosphere soils and root tissues of the three plant genotypes cultivated in these soils (Fig. 1).…”

“…Containers were randomly distributed in the growth chamber and moved each day. The plants were sampled after 34 days, corresponding to the appearance of a shoot ramification of order 2 (24).…”

Dynamics of the bacterial community structure in the rhizosphere of a maize cultivar

“…Some studies suggested that seasonal variations in the activity and relative abundance of rhizosphere bacterial communities are plant-dependent (Dunfield and Germida, 2003;Houlden et al, 2008;Mougel et al, 2006;Smalla et al, 2001). Although some research showed dynamic changes of maize rhizosphere bacterial community at different growth stages using culture-dependent (Cavaglieri et al, 2009;Nacamulli et al, 1997) and fingerprinting methods (Di Cello et al, 1997), detail phylogenetic compositions cannot be monitored due to low resolution of these approaches.…”