Role of plasmids in the formation of E. coli polycellular forms.

The formation of polycellular forms by E. coli strain K-12 cells containing F-like plasmids pAP22-2 and pAP42 was studied by the method of small-angle laser scattering. The efficiency and patterns of the resultant cell associations depend on genetic characteristics of the studied plasmids.

[Features of expression of the genetic region of plasmid pAP42, controlling the synthesis of "sex" pili and surface exclusion system in various E. coli cells]. / Osobennosti ékspressii geneticheskoi oblasti plazmidy pAP42, kontroliruiushchei sintez "polovykh" pilei i sistemu poverkhnostnogo iskliucheniia, v raznykh kletkakh E. coli.

The results of investigation of serologically--typed and nontyped E. coli cells carrying F-like derepressed plasmid pAP42 testified to the influence of genome of some bacterial hosts on the expression of plasmid genetic region determining "sex" (plasmid--specific) pili synthesis and surface exclusion system (Sfx--system). Similar changes in bacterial cells phenotype can also result from the mutational changes of this plasmid.

[The molecular cloning of a genetic region determining the surface exclusion system of the F-like plasmid pAP42]. / Molekuliarnoe klonirovanie geneticheskoi oblasti, determiniruiushchei sistemu poverkhnostnogo iskliucheniia F-podobnoi plazmidy pAP42.

Molecular cloning of genetic region of F-like plasmid pAP42, coding its surface exclusion system (system Six V) was performed. Restriction and genetic analysis of recombinant plasmids showed that six V locus is situated in Sal I-fragment f5 (4.2 MD) of this plasmid.

[Pili determined by the tra genes of F-like plasmids]. / Pili, determiniruemye tra-genami F-podobnykh plazmid.

The study of structural and functional features of plasmid-specific pili synthetized by E. coli cells under control of 27 F-like plasmids was performed. All the plasmids determined the pili of "flexible" type which were classified into 3 groups on the basis of difference in cell sensitivity to pili-specific phages f1, f2, Q. The possible role of transposons in the variation of pili functional properties was supposed.

[Systems of surface exclusion of F-like plasmids of E. coli and their genetic control]. / Sistemy poverkhnostnogo iskliucheniia F-podobnykh plazmid E. coli i ikh geneticheskii kontrol'.

The F-like plasmids belonging to 5 different Sfx-groups were discovered. The existence of atypical plasmids belonging to different Sfx-groups was shown. The molecular cloning of plasmid DNA fragment (3.9 mD) determining SfxII phenotype was performed.