Bio Microbiology - Spring 2012 Learning Guide 04.

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1 Bio Microbiology - Spring 2012 Learning Guide 04

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4 A septum assembles at the center of the cell. This molecular "purse string" is linked to the inner surface of the plasma membrane. As it contracts, it pulls the membrane together and separates the two cells. When growing under optimal conditions bacteria can divide as fast as once every minutes.

5 FtsZ is a protein encoded by the ftsz gene that assembles into a ring at the future site of the septum of bacterial cell division. This is a prokaryotic homologue to the eukaryotic protein tubulin. FtsZ has been named after "Filamenting temperature-sensitive mutant Z".

6 Cell topology and inhibitor gradients control place and time of cell division. Repression of FtsZ polymerization by polar localized proteins that exhibit a minimum of the repressor at midcell restricts the site of division ring. (A) E. coli s strategy depends on oscillation of the MinCD repressor from pole to pole. (B) Caulobacter establishes a gradient of the MipZ repressor with the highest concentration at the cell poles. (C) In S. pombe, the Pom1 repressor is localized to the poles. In small cells, the gradient of Pom1 extending from the poles overlaps at Cdr2 located at midcell and represses its activity. As the cell grows, the midcell repressor concentration diminishes until Cdr2 (and thus the Cdk1 pathway) is no longer repressed and entry into mitosis is facilitated.

7 E. Coli MinCDE system. MinD-ATP binds to a cell pole, also binds MinC, which prevents the formation of FtsZ polymers. The MinE ring causes hydrolysis of MinD s bound ATP, turning it into ADP and releasing the complex from the membrane. The system oscillates as each pole builds up a concentration of inhibitor that is periodically dismantled.

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9 A bacterial flagellum is only 0.01 µm thick and not directly visible in the light microscope. However, by treatment with a contrasting agent (tannin) the flagella can be made thicker, until they become visible. Often the flagella loose their natural curling during this procedure.

10 Tracks of swimming bacteria with polar flagellation. Overlaid frames with a time-dependent color code, observation period 5 sec

11 (a) Regular swimming motility powered by the rotation of flagellar filaments. (b) Sheathed flagella driven motility by spirochetes suitable in highly viscous fluids. (c) Swarming motility on a solid surface powered by multiple lateral flagellar filaments. (d) Social gliding motility resulting from the retraction of type IV pili adhered to a solid surface or other bacterial cell bodies. (e) Mechanism for adventurous gliding motility proposed by Mignot et al.

12 The helical shape of Borrelia burgdorferi (visible in the scanning electron micrograph) is imparted by the periplasmic flagella, which can be seen in the cross-sectional view of the spirochaete in the transmission electron micrograph.

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16 HOW BACTERIA ASSEMBLE FLAGELLA Robert M. Macnab Annual Review of Microbiology Vol. 57: (Volume publication date October 2003) (doi: /annurev.micro )

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20 Going against the grain: chemotaxis and infection in Vibrio cholerae Susan M. Butler & Andrew Camilli Nature Reviews Microbiology 3, (August 2005) doi: /nrmicro1207

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27 Electron Micrograph of the Nucleoid

28 Chromosome Structural Organization The Packing Problem!!

29 Chromosome attachment to the cell pole (A) The Caulobacter pars centromere bound to the ParB partition protein is attached to the cell pole by interaction with the polar PopZ polymeric network. The initiation of replication triggers the assembly of PopZ at the opposite pole, where it captures the duplicated copy of pars/parb. The diagram shows PopZ (red), ParB (green), PopZ + ParB (yellow), and chromosomes depicted as rings (dark green). (B) Sporulating cells of B. subtilis anchor chromosomes to the cell poles via the sporulation protein RacA, which binds to sites near the replication origin and to DivIVA at the cell poles. The images show RacA tagged with green fluorescent protein (green), the nucleoids (blue), and the cell membrane (red).

30 E. coli Salmonella

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32 Capsule surrounding cells of Klebsiella planticola

33 Poly-β-hydroxybutyrate (PHB) Sulfur globules

34 The intracytoplasmic membrane of Rhodobacter sphaeroides

35 Prochlorococcus marinus

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37 Structure and Mechanisms of a Protein-Based Organelle in Escherichia coli Shiho Tanaka, Michael R. Sawaya, Todd O. Yeates Science 1 January 2010: Vol no. 5961, pp DOI: /science Many bacterial cells contain proteinaceous microcompartments that act as simple organelles by sequestering specific metabolic processes involving volatile or toxic metabolites. Here we report the threedimensional (3D) crystal structures, with resolutions between 1.65 and 2.5 angstroms, of the four homologous proteins (EutS, EutL, EutK, and EutM) that are thought to be the major shell constituents of a functionally complex ethanolamine utilization (Eut) microcompartment.

38 Fig. 1 A model for the Eut microcompartment and its metabolic pathway. (A) A hypothetical model of the Eut microcompartment emphasizing the construction of a semiregular polyhedron primarily from hexameric shell proteins. (B) A model for the metabolism of ethanolamine in the Eut microcompartment.

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40 Bacterial Endospores

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42 Bacterial Endospores

43 The End