In most bacteria, cell division begins with the polymerization of the GTPase FtsZ at mid-cell, which recruits the division machinery to initiate cell constriction. In the filamentous bacterium... Show moreIn most bacteria, cell division begins with the polymerization of the GTPase FtsZ at mid-cell, which recruits the division machinery to initiate cell constriction. In the filamentous bacterium Streptomyces, cell division is positively controlled by SsgB, which recruits FtsZ to the future septum sites and promotes Z-ring formation. Here, we show that various amino acid (aa) substitutions in the highly conserved SsgB protein result in ectopically placed septa that sever spores diagonally or along the long axis, perpendicular to the division plane. Fluorescence microscopy revealed that between 3.3% and 9.8% of the spores of strains expressing SsgB E120 variants were severed ectopically. Biochemical analysis of SsgB variant E120G revealed that its interaction with FtsZ had been maintained. The crystal structure of Streptomyces coelicolor SsgB was resolved and the key residues were mapped on the structure. Notably, residue substitutions (V115G, G118V, E120G) that are associated with septum misplacement localize in the alpha 2-alpha 3 loop region that links the final helix and the rest of the protein. Structural analyses and molecular simulation revealed that these residues are essential for maintaining the proper angle of helix alpha 3. Our data suggest that besides altering FtsZ, aa substitutions in the FtsZ-recruiting protein SsgB also lead to diagonally or longitudinally divided cells in Streptomyces. Show less
Streptomyces present a valuable platform for natural product discovery. Lugdunomycin is a novel angucycline-derived polyketide from Streptomyces sp QL37, with unprecedented skeleton and... Show moreStreptomyces present a valuable platform for natural product discovery. Lugdunomycin is a novel angucycline-derived polyketide from Streptomyces sp QL37, with unprecedented skeleton and antimicrobial activity. This dissertation covers the research on the biosynthesis of this novel antibiotic and the developmental biology of Streptomyces. The data in this thesis have provided important new insights into the puzzle of lugdunomycin biosynthesis and the sporulation-specific cell division of Streptomyces. By means of molecular biology, structural biology, biochemical, chemical and bioinformatics approaches, we have uncovered the potential functions of the key enzymes, especially those encoded oxygenases (LugOI-LugOV) in lugdunomycin biosynthesis. Furthermore, we extensively studied the role of SsgB in Streptomyces development, that led us to the discovery of longitudinal cell division that support the predominant role of SsgB in the accurate positioning of the division site and the placement of the Z-ring. Show less
