For the digestion, genomic DNA containing agarose plugs were
equilibrated in 1 mL 1 SmaI buffer for 1 h with gentle agitation
and digested with 30 units of SmaI at 30 C overnight, and equilibrated
in 1 mL of 0.5 TBE buffer for 1 h prior to electrophoresis.
The agarose plugs were inserted into the wells of 1 g/100 mL PFGE
grade agarose gel (Bio-Rad) that was immersed in 0.5 TBE buffer.
The wells were covered with low melting temperature agarose.
Electrophoresis was performed in a CHEF DRII system (Bio-Rad,
California, USA) with 5.3e34.9 pulse times at 6 V/cm at 14 C for
20 h. In the end of electrophoresis run, the gel was stained in
600 mL dH2O containing 2 mg/100 mL of ethidium bromide for
45 min, and visualized in a gel documentation system (Vilber
Lourmat, France). For cluster analysis, the similarity among profiles
was calculated on the basis of the Dice’s coefficient. The dendrogram
was constructed according to the unweighted pair group
method with arithmetic averages clustering algorithm (UPGMA).