Candidatus Brocadia and Candidatus Kuenenia predominated in anammox bacterial community in selected Chinese paddy soils

Abstract

Anammox bacteria have been widely investigated in both natural aquatic habitats and wastewater treatment reactors. However, their distribution in agricultural ecosystems which receive high reactive nitrogen input is hardly known. This study aims to examine the distribution and diversity of anammox bacteria in different Chinese paddy soils and along soil profile horizons. DNA was extracted from paddy soils which were collected from ten sites and along four soil depth horizons (0-20, 20-40, 40-60, 60-80 cm). Community structure and diversity of the anammox bacteria were analyzed using cloning and sequencing methods by targeting 16S ribosomal RNA (rRNA) genes. Quantitative PCR was conducted to study the abundance of anammox hzsB genes. Anammox bacterial 16S rRNA genes were not detected in most of the surface soil profile layers but present in all subsurface and deep horizons. Two genera, Candidatus Brocadia and Candidatus Kuenenia, were the only groups detected, and the former was predominant in tested soils. A site-specific distribution pattern of anammox bacteria and significant relationship between anammox bacteria community composition and soil pH and ammonium concentration were observed. The abundance of anammox bacteria hzsB gene ranged from 3.78 x 10(4) to 1.64 x 10(7) per gram of dry soil in all soils and significantly varied along the soil profile horizons. Anammox bacteria were widely distributed in paddy soils, especially in subsurface and profile depth horizons. Candidatus Brocadia and Candidatus Kuenenia were the dominating anammox groups in the tested soils, and the two genera showed a site-specific distribution pattern across large Chinese paddy soil areas and along soil depth profiles