Cell shape and division septa positioning in filamentous <i>Streptomyces</i> require a functional cell wall glycopolymer ligase CglA

The cell wall of monoderm bacteria consists of peptidoglycan and glycopolymers in roughly equal proportions and is crucial for cellular integrity, cell shape, and bacterial vitality. Despite the immense value of <i>Streptomyces</i> in biotechnology and medicine as antibiotic producers, we know very little about their cell wall biogenesis, composition, and functions. Here, we have identified the LCP-LytR_C domain protein CglA (Vnz_13690) as a key glycopolymer ligase<i>,</i> which specifically localizes in zones of cell wall biosynthesis in <i>S. venezuelae</i>. Reduced amount of glycopolymers in the <i>cglA</i> mutant results in enlarged vegetative hyphae and failures in FtsZ-rings formation and positioning. Consequently, division septa are misplaced leading to the formation of aberrant cell compartments, misshaped spores, and reduced cell vitality. In addition, we report our discovery that c-di-AMP signaling and decoration of the cell wall with glycopolymers are physiologically linked in <i>Streptomyces</i> since the deletion of <i>cglA</i> restores growth of the <i>S. venezuelae disA</i> mutant at high salt. Altogether, we have identified and characterized CglA as a novel component of cell wall biogenesis in <i>Streptomyces</i>, which is required for cell shape maintenance and cellular vitality in filamentous, multicellular bacteria.IMPORTANCE<i>Streptomyces</i> are our key producers of antibitiotics and other bioactive molecules and are, therefore, of high value for medicine and biotechnology. They proliferate by apical extension and branching of hyphae and undergo complex cell differentiation from filaments to spores during their life cycle. For both, growth and sporulation, coordinated cell wall biogenesis is crucial. However, our knowledge about cell wall biosynthesis, functions, and architecture in <i>Streptomyces</i> and in other Actinomycetota is still very limited. Here, we identify CglA as the key enzyme needed for the attachment of glycopolymers to the cell wall of <i>S. venezuelae</i>. We demonstrate that defects in the cell wall glycopolymer content result in loss of cell shape in these filamentous bacteria and show that division-competent FtsZ-rings cannot assemble properly and fail to be positioned correctly. As a consequence, cell septa placement is disturbed leading to the formation of misshaped spores with reduced viability.