The soil samples were mixed volume-to-volume with a sterile
saline solution (KCl, 8.5 g/liter). 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.