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      Structured morphological modeling as a framework for rational strain design of Streptomyces species

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          Abstract

          Successful application of a computational model for rational design of industrial Streptomyces exploitation requires a better understanding of the relationship between morphology—dictated by microbial growth, branching, fragmentation and adhesion—and product formation. Here we review the state-of-the-art in modeling of growth and product formation by filamentous microorganisms and expand on existing models by combining a morphological and structural approach to realistically model and visualize a three-dimensional pellet. The objective is to provide a framework to study the effect of morphology and structure on natural product and enzyme formation and yield. Growth and development of the pellet occur via the processes of apical extension, branching and cross-wall formation. Oxygen is taken to be the limiting component, with the oxygen concentration at the tips regulating growth kinetics and the oxygen profile within the pellet affecting the probability of branching. Biological information regarding the processes of differentiation and branching in liquid cultures of the model organism Streptomyces coelicolor has been implemented. The model can be extended based on information gained in fermentation trials for different production strains, with the aim to provide a test drive for the fermentation process and to pre-assess the effect of different variables on productivity. This should aid in improving Streptomyces as a production platform in industrial biotechnology.

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          The online version of this article (doi:10.1007/s10482-012-9760-9) contains supplementary material, which is available to authorized users.

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          The regulation of the secondary metabolism of Streptomyces: new links and experimental advances.

          Streptomycetes and other actinobacteria are renowned as a rich source of natural products of clinical, agricultural and biotechnological value. They are being mined with renewed vigour, supported by genome sequencing efforts, which have revealed a coding capacity for secondary metabolites in vast excess of expectations that were based on the detection of antibiotic activities under standard laboratory conditions. Here we review what is known about the control of production of so-called secondary metabolites in streptomycetes, with an emphasis on examples where details of the underlying regulatory mechanisms are known. Intriguing links between nutritional regulators, primary and secondary metabolism and morphological development are discussed, and new data are included on the carbon control of development and antibiotic production, and on aspects of the regulation of the biosynthesis of microbial hormones. Given the tide of antibiotic resistance emerging in pathogens, this review is peppered with approaches that may expand the screening of streptomycetes for new antibiotics by awakening expression of cryptic antibiotic biosynthetic genes. New technologies are also described that have potential to greatly further our understanding of gene regulation in what is an area fertile for discovery and exploitation
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            Cytokinesis in bacteria.

            Work on two diverse rod-shaped bacteria, Escherichia coli and Bacillus subtilis, has defined a set of about 10 conserved proteins that are important for cell division in a wide range of eubacteria. These proteins are directed to the division site by the combination of two negative regulatory systems. Nucleoid occlusion is a poorly understood mechanism whereby the nucleoid prevents division in the cylindrical part of the cell, until chromosome segregation has occurred near midcell. The Min proteins prevent division in the nucleoid-free spaces near the cell poles in a manner that is beginning to be understood in cytological and biochemical terms. The hierarchy whereby the essential division proteins assemble at the midcell division site has been worked out for both E. coli and B. subtilis. They can be divided into essentially three classes depending on their position in the hierarchy and, to a certain extent, their subcellular localization. FtsZ is a cytosolic tubulin-like protein that polymerizes into an oligomeric structure that forms the initial ring at midcell. FtsA is another cytosolic protein that is related to actin, but its precise function is unclear. The cytoplasmic proteins are linked to the membrane by putative membrane anchor proteins, such as ZipA of E. coli and possibly EzrA of B. subtilis, which have a single membrane span but a cytoplasmic C-terminal domain. The remaining proteins are either integral membrane proteins or transmembrane proteins with their major domains outside the cell. The functions of most of these proteins are unclear with the exception of at least one penicillin-binding protein, which catalyzes a key step in cell wall synthesis in the division septum.
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              Positive control of cell division: FtsZ is recruited by SsgB during sporulation of Streptomyces.

              In bacteria that divide by binary fission, cell division starts with the polymerization of the tubulin homolog FtsZ at mid-cell to form a cell division scaffold (the Z ring), followed by recruitment of the other divisome components. The current view of bacterial cell division control starts from the principle of negative checkpoints that prevent incorrect Z-ring positioning. Here we provide evidence of positive control of cell division during sporulation of Streptomyces, via the direct recruitment of FtsZ by the membrane-associated divisome component SsgB. In vitro studies demonstrated that SsgB promotes the polymerization of FtsZ. The interactions are shown in vivo by time-lapse imaging and Förster resonance energy transfer and fluorescence lifetime imaging microscopy (FRET-FLIM), and are corroborated independently via two-hybrid studies. As determined by fluorescence recovery after photobleaching (FRAP), the turnover of FtsZ protofilaments increased strongly at the time of Z-ring formation. The surprising positive control of Z-ring formation by SsgB implies the evolution of an entirely new way of Z-ring control, which may be explained by the absence of a mid-cell reference point in the long multinucleoid hyphae. In turn, the localization of SsgB is mediated through the orthologous SsgA, and premature expression of the latter is sufficient to directly activate multiple Z-ring formation and hyperdivision at early stages of the Streptomyces cell cycle.
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                Author and article information

                Contributors
                +31-71-5274310 , g.wezel@chem.leidenuniv.nl
                Journal
                Antonie Van Leeuwenhoek
                Antonie Van Leeuwenhoek
                Antonie Van Leeuwenhoek
                Springer Netherlands (Dordrecht )
                0003-6072
                1572-9699
                21 June 2012
                21 June 2012
                October 2012
                : 102
                : 3
                : 409-423
                Affiliations
                [1 ]Molecular Biotechnology, Institute of Biology, Leiden University, PO Box 9505, 2300 RA Leiden, The Netherlands
                [2 ]Department of Biotechnology, Delft University of Technology, Julianalaan 67, 2628 Delft, The Netherlands
                Article
                9760
                10.1007/s10482-012-9760-9
                3456926
                22718122
                0b664dc5-2666-4513-98be-0a318e6cdd7a
                © The Author(s) 2012
                History
                : 3 April 2012
                : 30 May 2012
                Categories
                Original Paper
                Custom metadata
                © Springer Science+Business Media Dordrecht 2012

                Microbiology & Virology
                enzyme,ssga,antibiotic,morphological modeling,microscopy,fermentation
                Microbiology & Virology
                enzyme, ssga, antibiotic, morphological modeling, microscopy, fermentation

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