Life strategy of seed and root colonizing Massilia (Oxalobacteraceae)

The roots of plants are colonized by highly diverse bacterial lineages. For the majority of those, the traits conferring them rhizosphere competence are unknown. The life-strategy of a native cucumber seed- and root-colonizing population, belonging to the genus Massilia, was explored. This was done using culture- independent 16S rRNA gene-based techniques, including mass sequencing, quantitative real-time PCR and Fluorescent in situ hybridization. Over 75 percent of seed and root colonizing Oxalobacteraceae belonged to the genus Massilia. Populations of Massilia colonized and proliferated on the seed coat, seed radicle and roots, and were also attached to hyphae of the phytopathogen Pythium aphanidermatum infecting the seeds. Under low carbon availability medium conditions, rapid growth occurred during the transition from seed to root, and was followed by a substantial decay. Both growth and decay rate have increased by addition of energy sources on one hand and potential competitors on the other hand. In addition, Massilia absolute and relative abundance were significantly correlated in a positive exponential trend (R2=0.62, p<0.05). Therefore, a zymogenic and competition sensitive nature of root colonization by Massilia is suggested. Using this strategy, Massilia may achieve transient extraordinary domination of this ecological niche.