Sequencing and phylogenetic analysis
Plasmids were prepared with the QIAprep Miniprep Kit (Qiagen)
using the manufacturer’s protocol. The cloned fragment was
sequenced with a CEQ DTCS-quick start Kit (Beckman Coulter,
Fullerton, CA, USA) and a CEQ 8000 sequencing system (Beckman
Coulter) using the T7 forward primer.
Phylogenetically unusual nifH sequences were checked for chimeric
characteristics by comparing with the GenBank database
(DNA Databank of Japan, Shizuoka, Japan) using the blastn
program from BLAST search (2) with full-length and partial
sequences, and chimeric nifH sequences were omitted from later
analysis.