Diversity of active anaerobic ammonium oxidation (ANAMMOX) and nirK-type denitrifying bacteria in macrophyte roots in a eutrophic wetland

Abstract

Wetland eutrophication is a global ecological problem. Anaerobic oxidation of ammonium (ANAMMOX) and denitrification are the two major pathways of nitrogen removal in wetlands. However, little is known about the associated bacteria that are present around emergent macrophytes and their transcriptional activities. Here, we examine the transcriptional activity of bacteria that perform ANAMMOX and denitrification in the roots and vegetated sediments of three emergent macrophytes and in unvegetated sediment from a eutrophic wetland. Roots and vegetated sediments of three emergent macrophytes (Phragmites australis, Typha angustifolia, and Scirpus triqueter) and unvegetated sediment were collected from Wuliangsuhai wetland, China. The community structure and transcriptional activity of ANAMMOX and denitrifying bacteria were examined at the DNA and RNA levels. Additionally, the sediment physicochemical properties were determined. ANAMMOX (hzsB) and denitrifying bacteria (nirK, nirS, and nirSII) were detected in all sediments and roots at the DNA level. However, at the RNA level, root-associated ANAMMOX bacteria, including Candidatus Jettenia and Candidatus Brocadia, were detected only in the roots of P. australis. In contrast, nirK-carrying active denitrifiers, such as uncultured bacteria, Sinorhizobium, Rhizobiales, Mesorhizobium, Rhizobium, Devosia, and Bosea (all Rhizobiales), were detected in the roots of T. angustifolia and S. triqueter. The reduction of nitrogen concentration in the sediments of the vegetation zone was probably associated with active ANAMMOX bacteria and denitrifiers. Active root-associated ANAMMOX bacteria and nirK-type denitrifiers were influenced by plant species, and they likely contribute to nitrogen removal in eutrophic wetlands.