Streptomyces coelicolor A3(2) ftsI-and ftsW-null mutants produced aerial hyphae with no evidence of septation when grown on a traditional osmotically enhanced medium. This phenotype was partially suppressed when cultures were grown on media prepared without sucrose. We infer that functional FtsZ rings can form in ftsIand ftsW-null mutants under certain growth conditions. Rod-shaped bacteria that produce a peptidoglycan cell wall synthesize lateral-wall material during cell elongation and produce septa during cytokinesis. Most rod-shaped bacteria possess separate systems for these processes, each containing a protein of the SEDS (shape, elongation, division, and sporulation) family and a cognate class B penicillin-binding protein (PBP) (7, 9, 11). In Escherichia coli, the protein pairs involved in cell elongation and division are RodA-PBP2 and FtsW-FtsI (PBP3), respectively. However, some bacteria possess three protein pairs, as in Bacillus subtilis, where sporulation-specific division genes exist in addition to those for vegetative functions (15). Streptomyces coelicolor is a gram-positive, filamentous bacterium that requires cell division only for sporulation (13). Its genome possesses four homologous SEDS-PBP pairs (3).Here we report the characterization of S. coelicolor cell division genes ftsI and ftsW. We show that ftsI and ftsW are dispensable for colony formation but are required for efficient cell division. Similar to the ftsL and divIC mutants (2), the ftsIand ftsW-null mutants displayed medium-dependent phenotypic defects that are more severe on an osmotically enhanced medium. We suggest that because the ftsI and ftsW mutants are able to divide when grown on certain media, other proteins may compensate for the loss of FtsI and FtsW. Chains of spores are produced under certain growth conditions, implying that ladder-like arrays of Z rings (18) must be stably formed and function in the absence of FtsI and FtsW under certain conditions.Identification of ftsI and ftsW homologues in S. coelicolor. The S. coelicolor ftsI and ftsW homologues, ftsI Sc (StrepDB [http://streptomyces.org.uk/] accession number SCO2090) and ftsW Sc (accession number SCO2085), are located in the division and cell wall (dcw) cluster (Fig. 1). We determined the gene sequences prior to the S. coelicolor genome project. ftsI Sc is predicted to encode a 654-amino-acid, 69.5-kDa bitopic membrane protein with 26% (160/602) of its residues identical to B. subtilis PBP 2B (the FtsI homologue), 31% (188/604) identical to B. subtilis SpoVD (the sporulation-specific FtsI homologue), and 29% (175/586) identical to E. coli FtsI. ftsW Sc is predicted to encode a 456-amino-acid, 48-kDa integral membrane protein with 36% (128/351) of its residues identical to B. subtilis SpoVE (the sporulation-specific FtsW homologue), 36% (137/373) identical to B. subtilis FtsW (YlaO), and 31% (114/358) identical to E. coli FtsW. FtsW Sc lacks the unique C-terminal extension required for interaction with FtsZ in the related actinomycete Mycobacterium tuberculosis (...
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