Specific archaeal communities are selected on the root surfaces of ruppia spp. and phragmites australis

Abstract

Archaea, although being active members of microbial communities, have been poorly characterized in the rhizoplane of wetland plants. In this study, we compared the archaeal communities found on the root surface of Ruppia spp. and Phragmites australis. Four lagoons, two euhaline andtwo oligohaline, were sampled during two periods of the year.Archaeal communities were investigated by means of 16SrRNA gene cloning and sequencing. Archaeal sequencesclustered in 171 distinct Operational Taxonomic Units affiliatedto the Euryarchaeota (43 %), Crenarchaeota (36 %) andThaumarchaeota (21 %). Communities found in theunvegetated sediment samples showed a high variabilitymainly due to changes in the pH and conductivity. Ruppiaspp. roots exhibited a clear selection effect overHalobacteriales (>80 % of detected sequences) despite thgeographical location and sampling time. In contrast, thearchaeal community on the root surface of Phragmitesaustralis was largely dependent on the sampling locationand time. Methanogenic lineages were not found to be relevantin almost any of the analysed samples. Our findingssuggest that archaeal communities in the root surface of thestudied macrophytes are mainly composed (40 to 86 %) ofputative heterotrophic archaea, such as Halobacteriales,Thermoplasmatales and the Miscellaneous CrenarchaeoticGroup