12.2 Concept Check Purple bacteria are anoxygenic phototrophs that grow phototrophically, obtaining carbon from CO2+H2S (purple sulfur bacteria) or organic sources (purple nonsulfur bacteria). Some purple nonsulfur bacteria are highly physiologically diverse, and collectively, the photoautotrophic activities of purple bacteria can be of great ecological significance. The purple bacteria reside in the alpha, beta, or gamma subdivisions of the Proteobacteria.
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12.3-12.5 Concept Checks Chemolithotrophs are prokaryotes that can oxidize inorganic electron donors and in many cases use CO2 as their sole carbon source.
12.6 Concept Check Methylotrophs are prokaryotes able to grow on carbon compounds that lack carbon-carbon bonds. Some methylotrophs are also methanotrophs, able to grow on CH4. Two classes of methanotrophs are known, each having a number of structural and biochemical properties in common. Methanotrophs reside in water and soil and can also exist as symbionts of marine shellfish.
12.7-12.9 Concept Checks Pseudomonads include many gram-negative chemoorganotrophic aerobic rods; many N2-fixing species are phylogenically closely related, and can reduce N2 to NH3 in the process of nitrogen fixation. The acetic acid bacteria are also phylogenetically related to pseudomonads, and are characterized by an ability to oxidize ethanol to acetate aerobically.
12.11-12.12 Concept Checks The enteric bacteria are a large group of facultative aerobic rods of great medical and molecular biological significance. Vibrio and Photobacterium species are marine, and many species are bioluminescent.
12.13 Concept Check The Rickettsias are obligate intracellular parasites, many of which cause disease. Rickettsias are deficient in many metabolic functions, and obtain key metabolites from their hosts.
12.14 Concept Check Spirilla are spiral-shaped chemoorganotrophic prokaryotes widespread in the aquatic environment. The genera Helicobacter and Campylobacter are pathogenic spirilla. Spirilla are distributed among the alpha, beta, gamma, delta, and epsilon subdivisions of Proteobacteria.
12.15-12.16 Concept Checks Sheathed bacteria are filamentous Proteobacteria in which individual cells form a chain within an outer layer called the sheath. Budding and Prosthecate bacteria are appendaged cells that form stalks, or prosthecae, used for attachment or nutrient absorption, and are primarily aquatic.
12.17 Concept Check The fruiting myxobacteria are rod-shaped gliding bacteria that aggregate to form complex masses of cells called fruiting bodies. Myxobacteria are chemoorganotrophic soil bacteria that live by consuming dead organic matter, or other bacterial cells.
12.18 Concept Check Sulfate-and sulfur-reducing bacteria are a large group of delta Proteobacteria unified by their physiological process of reducing either SO42- or S° to H2S under anaerobic conditions. Two physiological subgroups of sulfate-reducing bacteria are known, group I, which is incapable of oxidizing acetate to CO2, and group II, which is capable of doing so.
12.19-12.20 Concept Checks The "Low GC" gram-positive bacteria are a large phylogenetic group that contains rods and cocci, sporulating and nonsporulating species. The production of endospores is a hallmark of the key genera Bacillus and Clostridium. Gram-positive bacteria are major agents for the degradation of organic matter in soil, and a few species are pathogenic.
12.21 Concept Check The mycoplasma group are is organisms that lack cell walls, and contain a very small genome. Many species require sterols to strengthen their membranes, and several are pathogenic for humans and other animals.
12.22 and 12.23 Concept Checks "High GC" gram-positive Bacteria include such organisms as Corynebacterium, Arthrobacter, Propionibacterium, and Mycobacterium. They are mainly harmless soil saprophytes but M. tuberculosis is the causative agent of the disease tuberculosis. M. tuberculosis cells have a lipid-rich, waxy outer surface layer that requires special staining procedures (the acid-fast stain) in order to observe the cells microscopically.
12.24 Concept Check The Streptomycetes are a large group of filamentous, gram-positive bacteria that form spores at the end of aerial filaments. Many clinically useful antibiotics like tetracycline and neomycin have come from Streptomyces species.
12.25 and 12.26 Concept Checks Cyanobacteria and prochlorophytes are oxygenic phototrophic prokaryotes. Prochlorophytes differ most clearly from cyanobacteria in that prochlorophytes contain chlorophyll b, and lack phycobilins. Oxygen in Earth's atmosphere is thought to have originated from cyanobacterial photosynthesis.
12.27 Concept Check Chlamydia are extremely small parasitic bacteria that cause a variety of human diseases. Chlamydia contain a very small genome, and are deficient in many metabolic functions.
12.28-12.31 Concept Checks The Planctomyces group contains stalked, budding bacteria, while the Flavobacteria contain a variety of gram-negative Bacteria motile by either flagella or by gliding associated with animals, food and the soil. Members of the Verrucomicrobia are distinguished by their multiple prosthecate cells.
12.32 Concept Check Green sulfur bacteria are obligately anaerobic anoxygenic phototrophs that produce unique structures called chlorosomes. These organisms can grow at very low light intensities and oxidize H2S to S° and SO42-.
12.33 Concept Check Spirochetes are tightly coiled, motile, helical prokarotes that contain both free-living, as well as pathogenic species.
12.34 and 12.35 Concept Checks Deinococcus and Chloroflexus are each key genera in separated major lineages of Bacteria. Deinococcus radiodurans is the most radiation resistant of all known organisms and Chloroflexus is an anoxygenic phototroph that shows photosynthetic properties characteristic of both purple bacteria and green bacteria.
12.36-12.38 Concept Checks Thermotoga, Thermodesulfobacterium, and Aquifex grow at high temperature, and each spearheads a major lineage of Bacteria. Aquifex is an H2-oxidizing chemolithotroph, while Thermotoga and Thermodesulfobacterium are both anaerobic chemoorganotrophs. Nitrospira and Defferibacter each form their own phylum.
