[New class of RP4 plasmid mutations inducing a mucoid-type of Escherichia coli K-12 cell growth].

A new class of mutations is described which induce mucoid growth of Escherichia coli K-12. Unlike classical capR and capS mutations, the mucoid phenotype of colonies of the cap forms obtained is determined by mutations in genomes of thermosensitive plasmids pEG1 and RP1-6Repts12, derivates of the RP1 Inc P1 Ap Tc Km factor and accompanied by a complete or partial loss of the thermosensitive character of maintenance. The morphological character induced by plasmids is not associated with changes in the sensitivity of bacteria to UV irradiation and is determined by superproduction of capsular polysaccharide differing in the chemical structure from colanic acid, a common capsular polysaccharide of E. coli K-12.