The amplified PCR products were gel fractionated on 12% polyacrylamide gel (37 acrylamide:1 bis-acrylamide) in a 1X DGGE buffer (40 mM Tris–HCl, 20 mM sodium acetate, 1 mM EDTA) using Hoefer vertical gel apparatus (SE600) for 150 min. at 300 V at 20 °C, using a circulating water bath temperature set to 20 °C.