All the samples were sonicated briefly in an ultrasonic bath, and enrichment cultures were prepared from a 1/5 dilution of the suspensions in poor broth (PB) nutrient medium (10 g/liter Bacto tryptone, 5 g/liter NaCl [pH 7]) and were incubated for 24 h at 28°C under shaking.
One hundred microliters of the enrichment cultures was plated onto PB or Luria-Bertani (LB) (10 g/liter Bacto tryptone, 5
g/liter yeast extract, 10 g/liter NaCl [pH 7]) agar plates supplemented with either 5 mMAs2O5, 5mMNa2HAsO4, or 10 MHgCl2, and the cultures were incubated for 1 week at 28°C. Colony types differing in shape, color, and margin were isolated and streak purified. The isolated strains were subcultivated onto LB agar alone or LB agar supplemented with 3% (wt/ vol) glucose for 1 week at 30°C, and strains with a mucoid phenotype were selected.