Cell Structure

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A Eukaryotic Flagellum and Cilium 9 + 2 microtubules

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Chemotaxis describes the movement of flagellated bacteria in response to chemical stimuli in their environment. The movement of bacteria is controlled by the propeller-like structure of the flagellum, which will move the bacterium towards a positive stimulus ( high conc of nutrients) and away from a negative stimulus ( toxins or antibiotics). Other types of tactic response in prokaryotes are: Phototaxis Aerotaxis Magnetotaxis

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Positive Bacterial Chemotaxis The outer ring is composed of bacteria consuming serine. The second ring was formed by E. coli consuming aspartate, a less powerful attractant. This colony is composed of motile, but non- chemo tactic mutants. Formed by non-motile bacteria

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Negative Bacterial Chemotaxis Negative chemotaxis by E. coli in response to the repellant acetate. The bright disks are plugs of concentrated agar containing acetate that have been placed in dilute agar inoculated with E. coli. Acetate concentration increases from zero at the top right to 3M at top left. Note the increasing size of bacteria-free zones with increasing acetate. The bacteria have migrated for 30 minutes.

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Endospores exhibit no signs of life, being described as cryptobiotic. They are highly resistant to environmental stresses such as high temperature, irradiation, strong acids, disinfectants, etc. Differences between endospores and vegetative cells

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Bacterial Endospore

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Early and Late Stages of Endospore Formation. During endospore formation, a vegetative cell is converted to a heat--resistant spore.

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Some Inclusions In Bacterial Cells

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Glycogen granules GLYCOGEN. Bacterial starch = poly-glucose. Carbon storage (often made when nitrogen is limited)

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PHB granules These compounds are poly-esters, hence plastics. Since made by microbes, they are BIODEGRADABLE

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Also known as Volutin or metachromatic granules Polyphosphates

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Sulfur globules Sulfur (Sulfide, thiosulfate) oxidizers frequently deposit elemental sulfur inside or outside cells.

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The reddish color is caused by purple sulfur bacteria.Some of the phototrophic bacteria contain gas vesicles and form sheets of several cells. The dark brownish- green, oval-shaped structures are phototrophic consortia. They are composed of several tightly attachedcells showing a well coordinated behavior. Gas vesicles Structures found in many aquatic microorganisms including archaea and eubacteria. Similar in all cases. Structures are cigar-shaped--very rigid. They are gas-filled and have a protein wall that allows gas but not water to pass. Hence, they create "empty space" in cells, and thereby buoyancy. High turgor pressures in cells can cause collapse of walls. Rate of synthesis and collapse can be used to position an organism in a water column.

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Magnetosomes Crystalline particles of iron oxide (magnetite = Fe3O4). They have a protein coat that may play a role in precipitating Fe+3. Not used for iron storage, but used to orient cells in magnetic field.

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Carboxysomes Polyhedral bodies found in many different autotrophs. Site of CO2 fixation and the enzyme ribulose 1, 5-bisphosphate carboxylase/oxygenase (RuBisCO) that is the primary site of carbon fixation.

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Phycobilisomes PHYCOBILISOMEs are antenna structures found in cyanobacteria and are found on the surface of the INTRACYTOPLASMIC MEMBRANES (THYLAKOIDS).

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CHLOROSOME are "sacs of Bchl" found in green sulfur bacteria--antenna for photosynthesis

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