Ltd., Tokyo, Japan). The denaturing gradient was from 27.5 learn more to 42.5% [100% corresponded to 7.08 M urea and 40% (wt/vol) formamide]. Gels were subjected to a constant
voltage of 50 V for 4 h at 60°C. After electrophoresis, the gels were stained for 20 min in ethidium bromide solution. DNA was visualized under UV light, digitally captured, and analyzed using a Gel Imaging System (Nippon Genetics Co. Ltd., Tokyo, Japan). (3) Cloning of PCR product and sequencing Prominent DNA bands from the DGGE gels were extracted and used as PCR templates with the forward primer PRBA338f without a GC clamp and the reverse primer PRUN518r. The nucleotide sequences obtained were compared with those of the 16S rRNA genes of the strains isolated. To analyze the full-length 16S rRNA gene sequences, specific primers were designed based on the partial sequences of the isolate that became more dominant in the culture during continuous growth in
basal medium containing 4-aminopyridine (Table 1). PCR amplification of part of the 3-hydroxy-4-pyridone dioxygenase gene The enrichment culture grown in 4-aminopyrdine-containing medium was harvested in the mid-exponential growth phase by centrifugation. Mixed genomic DNA in the cell pellets was Ku 0059436 extracted using Qiagen DNeasy Blood & Tissue Kit (Hilden, Germany) according to the manufacturer’s instructions and was used as a template for PCR. To amplify part of the 3-hydroxy-4-pyridone dioxygenase (3,4-dihydroxypyridine 2,3-dioxygenase) gene, pydA, the primers PydAf and PydAr were designed based
on the conserved region of previously reported dioxygenases from Rhizobium sp. TAL1145 (DDBJ/EMBL/GenBank accession no. AY729020), Hyphomicrobium Phospholipase D1 sp. MC1 (YP_004673996), Bordetella bronchiseptica RB50 (NP_890665), and Bordetella parapertussis 12822 (NP_885852) (Table 1). The following PCR protocol was used: initial denaturation at 95°C for 2 min; 35 cycles of denaturation at 95°C for 60 s, annealing at 45°C for 30 s, extension at 72°C for 30 s; and final extension at 72°C for 5 min. Harvesting of cells, preparation of mixed genomic DNA, and amplification were carried out in triplicate. Analytical methods The optical density (OD660) of the cultures was measured using a Hitachi U-2800 spectrophotometer. The 1H-NMR spectra of the isolated metabolites and the prepared standard compounds were measured with a Joel JNM-AL300 spectrometer (300 MHz, Joel Ltd., Tokyo, Japan). Released ammonia in the culture fluid was measured using the indophenol blue method [21]. Total protein in the culture was measured using the modified Lowry method, to confirm the utilization of 4-aminopyridine as a carbon, nitrogen, and energy source by the enrichment culture [22].