Ammonia-Oxidizing Archaea and Bacteria Differentially Contribute to Ammonia Oxidation in Sediments from Adjacent Waters of Rushan Bay, China.

Hui He,Zhigang Yu,Lulu Fu,Yu Zhen,Tiezhu Mi

doi:10.3389/fmicb.2018.00116

Abstract

Ammonia oxidation plays a significant role in the nitrogen cycle in marine sediments. Ammonia-oxidizing archaea (AOA) and bacteria (AOB) are the key contributors to ammonia oxidation, and their relative contribution to this process is one of the most important issues related to the nitrogen cycle in the ocean. In this study, the differential contributions of AOA and AOB to ammonia oxidation in surface sediments from adjacent waters of Rushan Bay were studied based on the ammonia monooxygenase (amoA) gene. Molecular biology techniques were used to analyze ammonia oxidizers’ community characteristics, and potential nitrification incubation was applied to understand the ammonia oxidizers’ community activity. The objective was to determine the community structure and activity of AOA and AOB in surface sediments from adjacent waters of Rushan Bay and to discuss the different contributions of AOA and AOB to ammonia oxidation during summer and winter seasons in the studied area. Pyrosequencing analysis revealed that the diversity of AOA was higher than that of AOB. The majority of AOA and AOB clustered into Nitrosopumilus and Nitrosospira, respectively, indicating that the Nitrosopumilus group and Nitrosospira groups may be more adaptable in studied sediments. The AOA community was closely correlated to temperature, salinity and ammonium concentration, whereas the AOB community showed a stronger correlation with temperature, chlorophyll-a content (chla) and nitrite concentration. qPCR results showed that both the abundance and the transcript abundance of AOA was consistently greater than that of AOB. AOA and AOB differentially contributed to ammonia oxidation in different seasons. AOB occupied the dominant position in mediating ammonia oxidation during summer, while AOA might play a dominant role in ammonia oxidation during winter.

Highlights

Nitrification is one of the most essential steps in the nitrogen cycle, including the microbial oxidation of ammonia to nitrite and subsequently to nitrate
The abundance of ammonia monooxygenase (amoA) gene could provide information concerning the potential ammonia-oxidizing activity, while the transcript activity of the amoA gene is a measure of protein production. Both the ratios of active Ammonia-oxidizing archaea (AOA) to total AOA and the ratios of active ammonia-oxidizing bacteria (AOB) to total AOB were less than 1%, which indicated that most of the AOA and AOB amoA genes are likely associated with inactive cells
Nitrosopumilus group of AOA and Nitrosospira group of AOB may be more adaptable in the studied sediments

Summary

Introduction

Nitrification is one of the most essential steps in the nitrogen cycle, including the microbial oxidation of ammonia to nitrite and subsequently to nitrate. As a membrane-bound enzyme, ammonia monooxygenase (AMO) is an important functional protein for ammonia oxidation and can oxide ammonium in AOA and AOB (Rotthauwe et al, 1997; Könneke et al, 2005). The amoA gene has been widely applied in molecular ecology research of AOA and AOB in different environments, such as lakes (Jiang et al, 2009; Hou et al, 2013b), wetlands (Ye et al, 2011; Sims et al, 2012a,b), soils (He et al, 2007; de Gannes et al, 2012; Wang et al, 2014; Zhao et al, 2015) and estuaries (Caffrey et al, 2007; Jin et al, 2011; Zheng et al, 2013). The relative contribution of AOA and AOB to ammonia oxidation is one of the most important issues related to the nitrogen cycle in the ocean

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Discussion

Conclusion