Geometric principles underlying the proliferation of a model cell system

SUMMARY Wall deficient variants of many bacteria, called L-forms, divide by a simple mechanism that does not depend on the complex FtsZ-based cell division machine. We have used microfluidic systems to probe the growth, chromosome cycle and division mechanism of Bacillus subtilis L-forms. The results show that forcing cells into a narrow linear configuration greatly improves the efficiency of cell growth and chromosome segregation. This reinforces the view that L-form division is driven by an excess accumulation of surface area over volume. Cell geometry was also found to play a dominant role in controlling the relative positions and movement of segregating chromosomes. The presence of the nucleoid appears to influence division both via a cell volume effect and by nucleoid occlusion, even in the absence of the FtsZ machine. Overall, our results emphasise the importance of geometric effects for a range of critical cell functions and are of relevance for efforts to develop artificial or minimal cell systems.