Stable isotope probing of bacterial community structure and gene expression in the rhizosphere of Arabidopsis thaliana.

The rhizosphere is an active compartment where plant and microorganisms establish a molecular dialogue. In this study, we analysed the impact of Arabidopsis thaliana on bacterial community structure and the expression of certain beneficial genes using DNA- and mRNA-SIP in the rhizosphere of plantlets grown under (13)CO(2) for 13, 21 and 27 days. DNA- and rRNA-SIP revealed changes in bacterial communities inhabiting the rhizosphere soil that were probably related to modification of root exudates, while root-colonizing populations were maintained over time suggesting their metabolic versatility and adaptation. The impact of the plant via root exudates on the expression of the noncoding RNAs rsmZ, acdS gene encoding 1-aminocyclopropane-1-carboxylate deaminase and nosZ gene encoding nitrous oxide reductase, in the root-adhering soil and on the roots of A. thaliana was determined using mRNA-SIP. Results showed that these genes were present and expressed by bacteria inhabiting roots and by those that derive nutrients from the breakdown of organic matter in soils or from root exudates. The expression of rsmZ under natural conditions indicates the importance of noncoding RNAs in bacterial adaptation to their ecological niches.