Distribution of Cold-Adapted Ammonia-Oxidizing Microorganisms in the Deep-Ocean of the Northeastern Japan Sea

Abstract

We investigated the quantities and phylogenies of amoA genes of ammonia-oxidizing archaea (AOA) belonging to Crenarchaeota and ammonia-oxidizing bacteria (AOB) belonging to Betaproteobacteria in water columns and deep-ocean cold seep sediment in the northeastern Japan Sea with a competitive PCR (cPCR) assay. Water samples were collected at depths of 2000 m and 2956 m. Sediment samples were collected where white bacterial mats had developed. The cPCR analysis revealed five to ten times more AOA than betaproteobacterial AOB in both the water columns and sediment. The abundance of the crenarchaeotal amoA gene was estimated at 6×10¹ and 3×10² copies ml^-1 in the water columns at depths of 2000 m and 2956 m, and 1×10⁸ and 1×10⁷ copies g^-1 in pelagic brown sediment and black sediment, respectively. Most archaeal amoA clones from water column at 2000 m fell into the Deep Marine Group. Most archaeal amoA clones from pelagic brown sediment were less closely related to known environmental clones. Moreover, incubation experiments revealed nitrite production at 4°C and 10°C. The results indicate that psychrophilic AOA and AOB may be responsible for nitrification in the deep-ocean region of the northeastern Japan Sea.