Distribution and Community Composition of Ammonia-Oxidizing Archaea and Bacteria in Coastal Sediments in Response to Sediment Material Gradients at Sendai Bay, Japan

Abstract

To examine how ammonia-oxidizing organisms in coastal sediments are affected by environmental changes, the distributions of ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB) were determined along an environmental gradient from the coastal mud to the offshore coarse sand at Sendai Bay, Japan. Sediment samples were collected in December 2011 and July 2012. The abundance of AOA ammonia monooxygenase alpha subunit gene (amoA) was high in the coastal muddy areas and low in the offshore sandy areas during both months. There was a strong positive correlation between AOA-amoA abundance and ammonia content in the sediment. AOB-amoA abundance was remarkably low in the muddy sediments in December. However, the distribution of AOB-amoA was similar to that of AOA-amoA in July. Clone library analysis indicated that the community composition for both types of organisms differed in sandy and muddy sediments and that the diversity was considerably lower in the muddy sediments during both months. These results suggest that the abundance of ammonia-oxidizing organisms was controlled by the ammonia levels in the sediment. However, there are some inhibitive conditions for AOB: presumably, the low organic matter supply to the surface oxic layer during autumn in the muddy sediment in Sendai Bay.