Genetic profiling of bacterial communities from the rhizospheres of ozone damaged Malva sylvestris (Malvaceae)

The phytotoxicity of tropospheric ozone at elevated concentrations can cause severe effects on plant vegetation. This study analyzed whether ozone-damaged plants transmit signals into the soil and thereby affect the structural diversity of bacteria inhabiting the rhizosphere. To generate highly stressful conditions, Malva sylvestris was raised from seeds under ozone exposure. Additionally, the plant age at the onset of ozone-stress was varied. Rhizosphere bacterial communities were analyzed by single-strand conformation polymorphism (SSCP) of PCR amplified partial 16S ribosomal RNA genes. None of these vigorous stress conditions caused a change in the genetic profiles targeting Bacteria with primers hybridizing to highly conserved regions in the 16S rRNA genes, despite visibly ozone-triggered injuries of the leaves and a reduced root biomass. Differences in the SSCP profiles however were observed between plants of different ages. In a more realistic scenario, plants raised in the greenhouse under normal atmospheric conditions were exposed to ozone episodes as they can occur during summer in industrialized countries of the northern hemisphere. To increase the sensitivity of detection, genetic profiles representing Alphaproteobacteria, Actinobacteria and Pseudomonas were analyzed separately in addition to those of Bacteria. None of the profiles showed any ozone-related alterations. In summary, the results of this study indicated that, even when the plants were visibly injured by ozone, the stress was not transmitted to the soil in a way that affected the structural diversity of the dominant rhizosphere bacterial community.