The inoculum used to establish the nitrifying cultures was obtained from the biofilter of a household-size freshwater fish tank. The tank housed five small tropical fish and nitrification occurred (i.e., NOstep step step 3 – was detected). The biofilter was selected for use as inoculum since the microbial community had adapted to a relatively low NHcuatro + condition (?500 ?M was typically measured in the influent to the biofilter) and the biofilter had been in stable operation for more than two years. The synthetic sponge filter (36 cm 2 ) was inoculated () into 60-ml serum bottles sealed with butyl rubber stoppers with 30 ml of synthetic medium containing 4 ?M KH2PO4, 10 ml/L mineral salts, 0.1 ml/L selenite/tungstate solution, and 1 ml/L trace metals (Biebl and Pfennig, 1978). After autoclaving, 3 ?l of filter-sterilized vitamin solution (Balch et al., 1979) were added, lds singles together with NH4Cl and NaHCO3 at final concentrations of 500 and 1,000 ?M, respectively. The NOB were eliminated by amending a separate set of cultures with sodium chlorate (10 mM) (Belser and Mays, 1980) until no NO3 – was detected in subsequent transfers. The cultures with NH4 + without chlorate are referred to as ‘Culture01,’ the ones with NH4 + and chlorate are ‘Culture02,’ while the Culture01 fed with NO2 – instead of NH4 + for experimental purposes are ‘Culture03.’ Cultures were grown at 25°C (akin to the temperature of the aquarium) in the dark without shaking (). Late exponential-phase cultures (?10% v/v) were routinely transferred to fresh media after an incubation period of about 5 to 7 days for 15 months (until the cultures became stable) before characterizations of the cultures were performed.
Characterizations of Cultures
All experiments were conducted in triplicate in 30 ml medium as described in Section “Cultivation of Nitrifiers” with 3 ml of late exponential-phase culture as inoculum. A range of NH4 + concentrations (50, 200, 500, 1,000, and 1,500 ?M) was used to test the growth rates of the nitrifiers in Culture01 and Culture02. The growth of NOB was tested using a range of NO2 – concentrations (50, 200, 500, 1,000, and 1,500 ?M) in Culture03. Different HCO3 – concentrations (1,000 and 3,000 ?M) were tested for all cultures. The potential inhibition effects of NO2 – on the AOB in Culture02 when grown with 500 ?M of NH4 + were studied by adding a range of NO2 – concentrations (500, 1,500, or 10,000 ?M). Liquid samples were withdrawn at regular intervals during the exponential phase (5–24 h) to determine the NH4 + , NO2 – and/or NO3 – concentrations, and the collected samples were filtered (0.2 ?m) prior to storage at -80°C. The ultimate dissolved oxygen concentration and pH of the cultures were measured using a portable oximeter (SevenGo Duo Pro-SG68, Mettler Toledo, Switzerland). The dissolved oxygen concentration was more than 5.6 mg/L and pH ranged from 6.8 to 7.0 in all cultures.
The fresh new constitution of bacterial groups try determined by event a beneficial part of the biofilter (thirty-six cm 2 ) and 20 ml away from Culture01 and you may Culture02 for DNA extraction using new PowerSoil DNA Isolation Package (Mo Bio Labs, Carlsbad, Ca, United states), since discussed prior to now (Lu et al., 2013). The fresh 515F/806R common primer couple (Caporaso ainsi que al., 2011) was utilized so you can amplify the V4 side of the 16S rRNA gene of one’s genomic DNA. Brand new PCR standards, amplicon filtering, and you can library preparing were because revealed before (Leung et al., 2014). The trials had been sequenced towards an Illumina MiSeq program (Genentech Business, Taipei, Taiwan), and that generated coordinated-prevent 250-bp checks out with ?sixty,000 paired-prevent raw reads for each and every sample.
Reads obtained from the sequencing system have been basic processed by removing the new barcodes and you can primers, with alignment of your checks out using Flash (V1.dos.7) (Magoc and you may Salzberg, 2011). New pass and you may reverse checks out provided similar efficiency, therefore the forward reads were used to have analysis. New aimed sequences was basically filtered with the QIIME pipeline (v.step one.8.0) (Caporaso mais aussi al., 2010b) into the program “split_library_fastq.py.” Chimera sequences was basically identified and you can eliminated with UCHIME (Edgar et al., 2011) up against the Gold databases (Bernal ainsi que al., 2001). OTU development try performed adopting the UPARSE pipe (Edgar, 2013) together with dereplicated reads was clustered towards OTUs in the a beneficial 97% series resemblance tolerance. Singleton OTUs was basically eliminated together with remaining large-high quality succession reads have been lined up with PyNAST (Caporaso ainsi que al., 2010a) up against the Ribosomal Database Opportunity (RDP, discharge 11.3).