Effect of Elevated Tropospheric Ozone on the Structure of Bacterial Communities Inhabiting the Rhizosphere of Herbaceous Plants Native to Germany

Abstract

Current elevated concentrations of ozone in the atmosphere, as they are observed during summer seasons, can cause severe effects on plant vegetation. This study was initiated to analyze whether ozone-stressed plants also transfer signals below ground and thereby alter the bacterial community composition in their rhizospheres. Herbaceous plants, native to Germany, with tolerance (Anthoxanthum odoratum, Achillea millefolium, Poa pratensis, Rumex acetosa, and Veronica chamaedrys) and sensitivity (Matricaria chamomilla, Sonchus asper, and Tanacetum vulgare) to ozone, raised in the greenhouse, were exposed in open-top chambers to two different ozone regimes, i.e., "summer stress" and a normal ozone background. DNA of bacterial cells from the rhizospheres was directly extracted, and partial sequences of the 16S rRNA genes were PCR amplified with primers targeting the following phylogenetic groups: Bacteria, ␣-Proteobacteria, Actinobacteria, and Pseudomonas, respectively. The diversity of the amplified products was analyzed by genetic profiling based on singlestrand conformation polymorphism (SSCP). Neither the tolerant nor the sensitive plants, the latter with visible above-ground damage, showed ozone-induced differences in any of the SSCP profiles, with the single exception of Actinobacteria-targeted profiles from S. asper. To increase the stress, S. asper was germinated and raised in the continuous presence of an elevated level of ozone. SSCP profiles with Bacteria-specific primers combined with gene probe hybridizations indicated an ozone-related increase in a Xanthomonas-related 16S rRNA gene and a decrease in the respective gene from the plant plastids. The fact that only this latter unrealistic scenario caused a detectable effect demonstrated that ozone stress has a surprisingly small effect on the structural diversity of the bacterial community in rhizospheres.

Structure and function of rhizosphere and non-rhizosphere soil microbial community respond differently to elevated ozone in field-planted wheat

“…This result indicated that fungi are possibly more responsive in the soil of O 3 -stressed early-successional tree species than are bacteria. This minor effect of O 3 on bacteria was corroborated by a study of the bacterial community inhabiting the rhizospheres of herbaceous plants after exposure to eO 3 , which the authors considered to have a surprisingly small effect on the structural diversity of the bacterial community (Dohrmann and Tebbe, 2005). In that study, genetic profiling based on single-strand conformation polymorphisms (SSCP) revealed that the different SSCP profiles generated from the bacterial community of the rhizospheres from O 3 -stressed and control plants were very similar and were not distinguished by statistical methods, which indicated that elevated levels of O 3 did not select for a different bacterial community composition.…”

“…Among previous examinations of soil microbial communities, very few have considered rhizosphere soil microbial responses to O 3 . The rhizosphere is the microbial habitat in the soil that is most strongly influenced by plants (Dohrmann and Tebbe, 2005). In several studies, the composition of root exudates, which mainly serve as C and energy sources for soil microorganisms (especially rhizosphere microbes), has been shown to strongly influence the structural and functional diversity of the microbial community (Kowalchuk et al, 2002;Miethling et al, 2000;Schmalenberger and Tebbe, 2003).…”

Contrasting patterns of seed and root colonization by bacteria from the genus Chryseobacterium and from the family Oxalobacteraceae

“…Physiological analyses of Telluria reveal many features that are consistent with traditional copiotrophic rhizosphere bacteria (Spiegel et al, 1991;Bowman et al, 1993;Anzai et al, 2000). Bacteria from the family Oxalobacteraceae, previously detected in root environments (Hallmann et al, 1997;Mahaffee and Kloepper, 1997a, b;Olsson et al, 1999;McSpadden-Gardner and Weller, 2001;Johansen and Binnerup, 2002;Schmalenberger and Tebbe, 2002;Graff and Conrad, 2005), have increasingly been seen as important components of rhizosphere communities and have been specifically targeted in rhizosphere studies (Dohrmann and Tebbe, 2005). Unlike the Oxalobacteraceae, the community composition of compost-derived Chryseobacterium was not sensitive to the seed or root environment.…”

Importance of soil organic matter for the diversity of microorganisms involved in the degradation of organic pollutants

“…The identification of DNA sequences recovered from bands of SSCP profiles followed the protocol described elsewhere, with three clones selected to identify each band of interest (Dohrmann and Tebbe, 2005).…”