chapter_22 - Chapter 22 Bacteria: The Proteobacteria 1 2...

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1 1 Chapter 22 Bacteria: The Proteobacteria 2 3 4 The Purple Nonsulfur Bacteria with one exception (genus Rhodocyclus) all are α - proteobacteria morphologically diverse most motile by polar flagella
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2 5 Purple nonsulfur bacteria… metabolically flexible normally grow anaerobically as anoxygenic photoorganoheterotrophs possess bacteriochlorophylls a or b in photosystems located in membranes that are continuous with plasma membrane some can use low levels of H 2 S as electron source in absence of light, most grow aerobically as chemoorganoheterotrophs in absence of light, some carry out fermentations and grow anaerobically found in mud and water of lakes and ponds with abundant organic mater and low sulfide levels; some marine species 6 Rickettsia and Coxiella genus Rickettsia class Alphaproteobacteria ; order Rickettsiales ; family Rickettsiaceae genus Coxiella class Gammaproteobacteria ; order Legionellales ; family Coxiellaceae considered together because of important similarities 7 Common features rod-shaped, coccoid, or pleomorphic typical gram-negative cell walls no flagella very small Rickettsia – 0.3 to 0.5 by 0.8 to 2.0 μ m Coxiella – 0.2 to 0.4 by 0.4 to 1.0 μ m parasitic or mutualistic parasitic species grow in vertebrate erythrocytes, macrophages, and vascular endothelial cells also live in blood-sucking arthropods, which serve as vectors or primary hosts 8 Parasitic life styles Rickettsia enters host by phagocytosis escapes phagosome reproduces in cytoplasm host cell bursts Coxiella enters host by phagocytosis remains in phagosome reproduces in phagolysosome host cell bursts
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3 9 Figure 22.3c Coxiella burnetti growing within fibroblast vacuole 10 Important pathogens Rickettsia prowazekii and Rickettsia typhi – typhus fever Rickettsia rickettsii – Rocky Mountain Spotted Fever Coxiella burnetti – Q fever many are important pathogens in dogs, horses, sheep, and cattle 11 The Caulobacteraceae and Hyphomicrobiaceae have at least one of three distinguishing features prostheca (pl., prosthecae) extension of cell, including plasma membrane, that is narrower than mature cell stalk nonliving appendage produced by cell and extending from it reproduction by budding progeny cell is a bud that first appears as a small protrusion on parent cell and enlarges to form mature cell 12 Genus Hyphomicrobium in class Hyphomicrobiaceae prosthecate, budding bacteria aerobic chemoheterotrophs grow on ethanol, acetate, and one-carbon molecules (facultative methylotroph) e.g., methanol, formate, and formaldehyde frequently attach to solid objects in aquatic and terrestrial environments may be 25% of total bacterial population in oligotrophic (nutrient-poor) freshwater habitats
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4 13 Figure 22.5 Life cycle of Hyphomicrobium 14 Genus Rhizobium
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chapter_22 - Chapter 22 Bacteria: The Proteobacteria 1 2...

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