Metabolic cooperation between Bacillus subtilis and Escherichia coli.

Though microbial species of both Bacillus subtilis and Escherichia coli have been extensively analyzed as to their physiological and genetic characteristics, little attention has been paid to their mutual relationship. Wereport here our observation that mixed cultures of auxotrophic cells of B. subtilis and E. coli can grow on minimal glucose agar, indicating a probable metabolic cooperation. Auxotroph strains of B. subtilis and E. coli were used. A strain named Sh of E. coli B/r requiring isoleucine and valine for growth in addition to tryptophan was isolated after treatment with TV-methyl-JV'-nitro-TV-nitrosoguanidine from E. coli B/r WP2 trp of Witkin.1* A strain named NIG11212) of B. subtilis requiring histidine and methionine was prepared as a leu+ transformant ofHA101 (his met leu) with DNAof strain 168T requiring thymine but wild as to leucine biosynthesis. The minimal glucose agar mediumconsisted of a modified Vogel-Bonner's minimal salts solution containing per liter, 1 g (NH4)2SO4, 10g KH2PO4, 0.1g MgSO4-7H2O and 0.5g Na3 citrate, neutralized with KOH (about 1.94 g required), supplemented with 4 g glucose and solidified with 1.5% Difco agar. The bacteria were cultured in liquid B2 broth which contained 10g wet Kyokuto beef extract, 10 g dry powder of Daigo polypeptone and 5% NaCl per liter, adjusted to pH 7.0. Use of this kind of complex mediumwas essential to obtain the results described below. Difco nutrient broth could be used. However, bacteria precultured in Difco Penassay mediumdid not exhibit the phenomenon. When bacteria of B. subtilis NIG1121