Abstract
Bacterial cell division is a highly complex process that requires tight coordination between septum formation and chromosome replication and segregation. In bacteria that divide by binary fission a single septum is formed at mid-cell, a process that is coordinated by the conserved cell division scaffold protein FtsZ. In contrast, during sporulation-specific cell division in streptomycetes, up to a hundred rings of FtsZ (Z rings) are produced almost simultaneously, dividing the multinucleoid aerial hyphae into long chains of unigenomic spores. This involves the active recruitment of FtsZ by the SsgB protein, and at the same time requires sophisticated systems to regulate chromosome dynamics. Here, we show that SepG is required for the onset of sporulation and acts by ensuring that SsgB is localized to future septum sites. Förster resonance energy transfer imaging suggests direct interaction between SepG and SsgB. The beta-lactamase reporter system showed that SepG is a transmembrane protein with its central domain oriented towards the cytoplasm. Without SepG, SsgB fails to localize properly, consistent with a crucial role for SepG in the membrane localization of the SsgB–FtsZ complex. While SsgB remains associated with FtsZ, SepG re-localizes to the (pre)spore periphery. Expanded doughnut-shaped nucleoids are formed in sepG null mutants, suggesting that SepG is required for nucleoid compaction. Taken together, our work shows that SepG, encoded by one of the last genes in the conserved dcw cluster of cell division and cell-wall-related genes in Gram-positive bacteria whose function was still largely unresolved, coordinates septum synthesis and chromosome organization in Streptomyces.
Highlights
Most unicellular bacteria grow and divide by binary fission, which involves an increase in cell length, chromosome replication and segregation, and septum formation, eventually resulting in two daughter cells that each inherits a single copy of the chromosome
To be able to recruit FtsZ, SsgB needs to dock to the membrane, and the lack of a membrane domain suggests that another protein ensures its membrane attachment
The canonical control systems and septum-localizing proteins (Min, Noc, FtsA, ZipA, ZapA, EzrA, etc.) found in bacteria that divide by binary fission are all absent in streptomycetes, and instead actinomycete-specific proteins control the localization of the septa
Summary
Most unicellular bacteria grow and divide by binary fission, which involves an increase in cell length, chromosome replication and segregation, and septum formation, eventually resulting in two daughter cells that each inherits a single copy of the chromosome. Streptomycetes are filamentous Gram-positive soil bacteria that have a complex multicellular life cycle [11,12], and produce over 60% of all known antibiotics and many other bioactive natural products [13,14]. Expression of these natural products is typically coordinated with the onset of spore development [15]. During sporulation-specific cell division, FtsZ initially assembles in long filaments in the aerial hyphae, as regular foci, to form a ladder of Z rings [17]. Cytokinesis results in long chains of spores, following a complex process of coordinated cell division
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
