Relaxation Motions Induced in Bacillus subtilis Macrofibres by Cleavage of Peptidoglycan

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Abstract
Bacillus subtilis macrofibres exposed to lysozyme underwent characteristic rotations, termed relaxation motions, in which their twist changed. Intact macrofibres and macrofibre fragments devoid of loop ends responded in the same way. Macrofibre strains for which the helix hand is temperature-dependent and also those of fixed-hand (both left and right) underwent initial relaxation motions towards the right-hand end of the twist spectrum, the only exception being those in which the initial twist state was at or near the right-hand maximum. Often when the initial relaxation motions were completed immediately before structure breakdown the macrofibres underwent one or a few rotations in the opposite direction (towards the left-hand end of the twist spectrum). Crude autolysin extract obtained from wild-type B. subtilis also caused macrofibre relaxation motions at pH 5.6 but at pH 8.0 macrofibre breakdown occurred as a result of septal cleavage. This resulted in the release of helically shaped individual cellular filaments. These findings suggest that strain in the cell wall associated with helical shape was dependent on the integrity of the glycan backbone rather than peptide cross-bridges. In contrast, cleavage of peptide cross-bridges apparently was instrumental in the cell separation process. Left- and right-hand macrofibres, when exposed to lysozyme, exhibited different rates of relaxation, breakdown of fibre structure and protoplast formation. Similarly, the rate of macrofibre breakdown during the lag between temperature shift and inversion reflected the replacement of septal wall material by that of a new conformation corresponding to the new helix hand. The difference in the rates of protoplast formation indicates asymmetry in the overall rate of cleavage by lysozyme which may reflect the activity of left-twist protein(s).