Ant pharming: antibacterial polyketides from plant-ant associated bacteria.
Polarized growth in eukaryotes requires polar multiprotein complexes. Here, we establish that selection and maintenance of cell polarity for growth also requires a dedicated multiprotein assembly in the filamentous bacterium, Streptomyces coelicolor. We present evidence for a tip organizing center and confirm two of its main components: Scy (Streptomyces cytoskeletal element), a unique bacterial coiled-coil protein with an unusual repeat periodicity, and the known polarity determinant DivIVA. We also establish a link between the tip organizing center and the filamentforming protein FilP. Interestingly, both deletion and overproduction of Scy generated multiple polarity centers, suggesting a mechanism wherein Scy can both promote and limit the number of emerging polarity centers via the organization of the Scy-DivIVA assemblies. We propose that Scy is a molecular "assembler," which, by sequestering DivIVA, promotes the establishment of new polarity centers for de novo tip formation during branching, as well as supporting polarized growth at existing hyphal tips.bacterial polarized growth | polar multiprotein assembly | cell division | modified hendecad coiled coil H ow organisms, cells, or tissues establish polarity is one of the fundamental questions in developmental biology. In eukaryotes, from unicellular organisms to multicellular plants and animals, some of the core mechanisms for generating polarity are conserved (1). Sites for polarization must be selected using positional markers, followed by the recruitment of a complex assembly, which, in turn, orients cytoskeletal filaments that deliver vesicles to the particular sites. A specific example of polarity is polarized growth, during which cells select a single polarization site and generate elongated, cylindrical shapes, such as neuronal dendrites in animals, root hairs and pollen tubes in plants, hyphal growth of filamentous fungi, elongation of Schizosaccharomyces pombe, or the short period of polarized growth during budding in Saccharomyces cerevisiae. However, the presumed earliest examples of polarized growth can be found in bacteria. These include the actinomycete Streptomyces coelicolor, which is used as a model organism for studying morphological differentiation and filamentous growth.The complex life cycle of S. coelicolor begins with an ovoid spore that contains a single chromosome. During germination, long, multigenomic filaments (germ tubes) are formed, which branch regularly to generate a network of hyphal filaments. Branching is a necessity for exponential growth because the rate of tip elongation cannot exceed a certain maximum; hence, there is an exponential increase in the number of new tips. New tips develop on the lateral wall well behind the existing tip, a phenomenon also observed and described as apical dominance in eukaryotic filamentous fungi. When grown on semisolid agar medium, these hyphal filaments first grow across and into the solid medium, generating the vegetative mycelium, followed by the formation of an aerial mycelium by h...
Highlights d c-di-GMP controls development in the multicellular bacterium Streptomyces d c-di-GMP mediates complex formation between sporulation s, s WhiG , and anti-s, RsiG d RsiG uses two novel E(X) 3 S(X) 2 R(X) 3 Q(X) 3 D signature motifs to bind two c-di-GMPs d When c-di-GMP levels drop, s WhiG is released to activate late sporulation regulators
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