Postdivisional synthesis of the Sporosarcina ureae DNA translocase SpoIIIE either in the mother cell or in the prespore enables Bacillus subtilis to translocate DNA from the mother cell to the prespore

Abstract

The differentiation of vegetative cells of Bacillus subtilis into spores involves asymmetric cell division, which precedes complete chromosome partitioning. The DNA translocase SpoIIIE is required to translocate the origin distal 70% of the chromosome from the larger mother cell into the smaller prespore, the two cells that result from the division. We have tested the effect of altering the time and location of SpoIIIE synthesis on spore formation. We have expressed the spoIIIE homologue from Sporosarcina ureae in B. subtilis under the control of different promoters. Expression from either a weak mother cell-specific (sigma(E)) promoter or a weak prespore-specific (sigma(F)) promoter partly complemented the sporulation defect of a spoIIIE36 mutant; however, expression from a strong prespore-specific (sigma(F)) promoter did not. DNA translocation from the mother cell to the prespore was assayed using spoIIQ-lacZ inserted at thrC; transcription of spoIIQ occurs only in the prespore. Translocation of thrC::spoIIQ-lacZ into the prespore occurred efficiently when spoIIIE(Su) was expressed from the weak sigma(E)- or sigma(F)-controlled promoters but not when it was expressed from the strong sigma(F)-controlled promoter. It is speculated that the mechanism directing SpoIIIE insertion into the septum in the correct orientation may accommodate slow postseptational, prespore-specific SpoIIIE synthesis but may be swamped by strong prespore-specific synthesis.

FIG. 1.

Schematic representation of the replacement of the P_spac promoter driving expression of spoIIIE_Su transcription in B. subtilis SL7870 by double-crossover recombination with linearized pVK149 to yield SL7980.

FIG. 2.

Translocation of thrC::P_spoIIQ-lacZ from the mother cell into the prespore. Bacteria were incubated in MSSM and assayed for β-galactosidase activity, which is induced upon entry of thrC::P_spoIIQ-lacZ into the prespore. All strains contained the thrC::P_spoIIQ-lacZ fusion. Solid circles, spo⁺ (SL8509); open triangles, spoIIIE36 (SL8776); solid squares, spoIIIE36 P_spoIID-spoIIIE_Su (SL8808); open squares, spoIIIE36 P_spoIIR-spoIIIE_Su (SL10406); open circles, spoIIIE36 P_spoIIQ-spoIIIE_Su (SL7980).

FIG. 3.

Relative strengths of promoters assessed with transcriptional lacZ fusions. Bacteria were incubated in MSSM and assayed for β-galactosidase activity. Solid circles, spoIIIE36 (SL8776); filled triangles, spoIIIE36 ppsD::P_spoIID-lacZ (SL9559); open circles, spoIIIE36 amyE::P_spoIIR-lacZ (SL10616); open squares, spoIIIE36 amyE::P_spoIIQ-lacZ (SL9319); solid squares, spoIIIE::spc amyE::P_spoIIQ-lacZ (SL11134).