Cellulose-negative Mutants of Acetobacter xylinum

Summary: Cellulose-negative mutants of Acetobacter xylinum have been isolated. Chemical mutagenesis induced a high frequency of such mutants without significant cell killing. Cellulose synthesis could be activated phenotypically in the majority of the mutants by antibiotics that block RNA or protein synthesis. Therefore these mutations are not in the structural genes coding for the enzymes involved in cellulose synthesis, but their nature is not known. All of the spontaneous cellulose-negative mutants and the mutants induced by ethyl methanesulphonate or nitrous acid reverted when grown statically, but about 10% of the nitrosoguanidine-induced mutants did not. Growth experiments with mixed cultures of the wild-type and cellulose-negative mutants were used to analyse the biological function of cellulose in A. xylinum. The cellulose-producing wild-type has a strong selective advantage compared with the cellulose-negative mutants when grown statically. This is in agreement with the hypothesis (Schramm & Hestrin, 1954) that cellulose enables the cells to reach the surface of the liquid medium, where the supply of oxygen is abundant. Cellulose-negative mutants may be enriched in shake flask cultures because of selective aggregation of cellulose-producing cells.