“…Sulfur compounds were obtained from Sigma Chemical Co. (St. Louis, Mo.) or Aldrich Chemical Co., Inc. (Milwaukee, Wis.), and to minimize decomposition (24), they were dissolved in water just prior to use, filter sterilized, and added to cooled-down R2MM-S agar. Plasmids pKC505 (26) and pAL7180 (12) were obtained from Nagaraja Rao, Eli Lilly Laboratories, and from Leonard Katz, Abbott Laboratories, respectively.…”