Gelatin-induced reversion of protoplasts of Bacillus subtilis to the bacillary form: biosynthesis of macromolecules and wall during successive steps.
Protoplasts of Bacillus subtilis plated on SDG medium formed L colonies in quantative yield and propagated in the L-form indefinitely. Protoplasts or L bodies placed in 25% gelatin medium formed bacillary colonies. Details of the reversion of these naked bodies to the walled form are reported here. Protoplasts prepared in minimal medium reverted fairly synchronously 3 to 4 hr after inoculation into gelatin, but protoplasts preincubated in casein hydrolysate (CH)-enriched minimal medium were primed to revert within 1 hr in the gelatin. Preincubation for 1.5 hr in 0.44% CH was required for good priming. Cells must be subjected to this preincubation (step 1) in the naked state; it is effective for L bodies as well as protoplasts. Priming was blocked by chloramphenicol, puromycin, and actinomycin D but was not affected by penicillin, lysozyme, or inhibition of deoxyribonucleic acid (DNA) synthesis. It is concluded that protein and ribonucleic acid (RNA) synthesis are required during step 1, that DNA synthesis is not required, and that wall mucopeptide is not made. The reversion of well-primed protoplasts in the gelatin (step 2) proceeded undisturbed in thymine-starved cells with chromosomes arrested at the terminus. It was scarcely slowed by chloramphenicol in the gelatin but was delayed about 3 hr by both puromycin and actinomycin D. Escape from inhibition occurred while the inhibitors were still actively blocking growth. Penicillin and cycloserine inhibited and lysozyme reversed reversion. Momentary melting of the gelatin delayed reversion. It is concluded that mucopeptide synthesis occurs in step 2, that concomitant RNA, DNA, or protein synthesis is not essential, but that physical immobilization of excreted cell products at the protoplast surface is necessary early in step 2. Newly reverted cells were misshapen and osmotically sensitive. Processes which confer osmotic stability after reversion (step 3) did not occur in the presence of chloramphenicol or actinomycin D.