Abstract
Nitrifying biofilters are used in aquaria and aquaculture systems to prevent accumulation of ammonia by promoting rapid conversion to nitrate via nitrite. Ammonia-oxidizing archaea (AOA), as opposed to ammonia-oxidizing bacteria (AOB), were recently identified as the dominant ammonia oxidizers in most freshwater aquaria. This study investigated biofilms from fixed-bed aquarium biofilters to assess the temporal and spatial dynamics of AOA and AOB abundance and diversity. Over a period of four months, ammonia-oxidizing microorganisms from six freshwater and one marine aquarium were investigated at 4–5 time points. Nitrogen balances for three freshwater aquaria showed that active nitrification by aquarium biofilters accounted for ≥81–86% of total nitrogen conversion in the aquaria. Quantitative PCR (qPCR) for bacterial and thaumarchaeal ammonia monooxygenase (amoA) genes demonstrated that AOA were numerically dominant over AOB in all six freshwater aquaria tested, and contributed all detectable amoA genes in three aquarium biofilters. In the marine aquarium, however, AOB outnumbered AOA by three to five orders of magnitude based on amoA gene abundances. A comparison of AOA abundance in three carrier materials (fine sponge, rough sponge and sintered glass or ceramic rings) of two three-media freshwater biofilters revealed preferential growth of AOA on fine sponge. Denaturing gel gradient electrophoresis (DGGE) of thaumarchaeal 16S rRNA genes indicated that community composition within a given biofilter was stable across media types. In addition, DGGE of all aquarium biofilters revealed low AOA diversity, with few bands, which were stable over time. Nonmetric multidimensional scaling (NMDS) based on denaturing gradient gel electrophoresis (DGGE) fingerprints of thaumarchaeal 16S rRNA genes placed freshwater and marine aquaria communities in separate clusters. These results indicate that AOA are the dominant ammonia-oxidizing microorganisms in freshwater aquarium biofilters, and that AOA community composition within a given aquarium is stable over time and across biofilter support material types.
Highlights
Ammonia (NH3) is toxic to fish at concentrations exceeding 0.1 mg NH3-N L21 [1], which can be problematic for confined ecosystems such as ornamental aquaria, ponds, and recirculating aquaculture systems
Ammonia Oxidation in Aquarium Biofilters scaling (NMDS) based on denaturing gradient gel electrophoresis (DGGE) fingerprints of thaumarchaeal 16S rRNA genes placed freshwater and marine aquaria communities in separate clusters. These results indicate that Ammonia-oxidizing archaea (AOA) are the dominant ammonia-oxidizing microorganisms in freshwater aquarium biofilters, and that AOA community composition within a given aquarium is stable over time and across biofilter support material types
To understand AOA and ammonia-oxidizing bacteria (AOB) temporal abundance, samples from six freshwater and one marine aquarium biofilter were collected over a period of 79–113 days
Summary
Ammonia (NH3) is toxic to fish at concentrations exceeding 0.1 mg NH3-N L21 [1], which can be problematic for confined ecosystems such as ornamental aquaria, ponds, and recirculating aquaculture systems. Ammonia-oxidizing bacteria (AOB) belonging to the b- and c-Proteobacteria were thought to be solely responsible for nitrification in aquarium biofilters and other natural and engineered environments [2]. This idea was challenged by the isolation of Nitrosopumilus maritimus, an autotrophic archaeon that gains energy through the oxidation of ammonia to nitrite [3]. High substrate affinity of AOA (e.g. Km 51.86–9.66 mg N L21 total ammonia for N. maritimus) may enable adaptation to limited nutrient conditions [19, 20] and explain the presence of AOA in natural oligotrophic environments with low ammonia concentrations [21, 22]
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