Streptomyces uses both polar and dispersed cell wall synthesis during exploratory growth

Bacterial cell growth involves expansion of the peptidoglycan cell wall. Three mutually exclusive peptidoglycan synthesis mechanisms exist in bacteria: MreB-dependent dispersed growth in many rod-shaped bacteria, polar growth involving specific proteins in actinobacteria and rhizobiales, and septal growth involving FtsZ in many cocci. Here we used imaging, mass spectrometry analysis of peptidoglycan composition, bacterial genetics and colocalization analyses to show that the actinobacterium Streptomyces venezuelae uses both canonical polar peptidoglycan synthesis and MreB-dependent dispersed peptidoglycan synthesis during rapid, exploratory growth. Transmission electron microscopy and peptidoglycan analyses showed changes in cell wall structure and composition with exploratory growth. MreB1 was essential for cell wall integrity and culture viability during exploratory growth and also localized to side walls in regions of new growth. Our results show that MreB1 is required for dynamic cell wall changes over the course of a growth cycle, contributing to a wall that is structurally distinct from that of conventionally growing streptomycetes.