Transcript Chapter 21
Chapter 21 Bacteria: The Deinococci and Nonproteobacteria Gram Negatives 1 Life on Earth evolved along three major lines, called domains, all derived from a common ancestor. Each domain contains several phyla. The domains, Bacteria and Archaea, remained prokaryotic, whereas the third, Eukarya, evolved into the modern eukaryotic cell. 2 Aquificae and Thermotogae • Thermophiles that grow at temperatures above 85° C -Aquificae and Thermotogae Figure 21.1 3 4 Phylum Aquificae • Thought to be deepest (oldest) branch of Bacteria • Contains one class, one order, and five genera – two best studied genera are Aquifex and Hydrogenobacter 5 Genus Aquifex • Thermophile with a growth optimum of 85°C and a maximum of 95°C • Microaerophilic • Chemolithoautotroph -uses hydrogen, thiosulfite, and sulfur as electron donor -uses oxygen as electron acceptor -genome ~1/3 size of E. coli 6 Phylum Thermotogae • Second deepest branch of Bacteria • Contains one class, one order, and six genera – best studied genus is Thermotoga 7 Genus Thermotoga • Gram-negative rods – have outer sheathlike envelope that can balloon out from ends of cell • Thermophiles – optimum 80°C; maximum 90°C – grow in active geothermal areas – terrestrial solfataric springs 8 Thermotoga… • Chemoheterotrophs – have functional glycolytic pathway – can grow anaerobically on carbohydrates and proteins digests • e.g., Thermatoga maritima – ~24% of coding sequences are similar to archaeal genes 9 Figure 21.2 10 Deinococcus-Thermus 11 Genus Deinococcus • Deinococcus is best studied • Spherical or rod-shaped – associated in pairs or tetrads – stain gram-positive but do not have typical gram-positive cell wall • layered outer membrane similar to gram-negatives • L-ornithine in peptidoglycan • lacks teichoic acid 12 Figure 21.3 13 14 Deinococcus… • Mesophilic • Mesophilc, aerobic, produce acid • Extraordinarily resistant to desiccation and radiation – can survive 3-5 million rad (100 rad lethal to humans) • Isolated from ground meat, feces, air, fresh water, and other sources, but natural habitat unknown 15 Deinococcus…… • Genome consists of two circular chromosomes, a megaplasmid, and a small plasmid – radiation resistance due to ability to repair genome when it is severely damaged • Rapidly repairs fragmented DNA within 12-24 hours when exposed to radiation • D. radiodurans shown to have an efficient DNA repair system 16 Photosynthetic Bacteria • Three groups of photosynthetic bacteria – the purple bacteria – the green bacteria – the cyanobacteria • differ from the purple and green bacteria by carrying out oxygenic photosynthesis – have two photosystems – use water as an electron donor and generate oxygen during photosynthesis 17 Purple sulfur bacteria Alga Bloom of Purple Sulfur Bacteria, Sulfide Spring, Madison, WI 18 19 differences in absorption spectra correlates with ecological distribution Figure 21.4 20 21 Taxonomy of Photosynthetic Bacteria • • • • Phylum Chloroflexi – green nonsulfur bacteria Phylum Chlorobi – green sulfur bacteria Phylum Cyanobacteria Phylum proteobacteria purple bacteria – purple sulfur bacteria – purple non-sufur bacteria • phylum Firmicutes – heliobacteria 22 Purple sulfur bacteria: Note the sulfur granules deposited inside the cells 23 Green sulfur bacteria: Note the sulfur granules deposited outside the cells Copyright © The McGraw-Hill Companies, Inc. 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Purple bacteria Chlorosomes from green bacteria 24 Halophilic Purple bacteria Phylum Chlorobi • Green sulfur bacteria • Morphologically diverse – rods, cocci, or vibrios; single cells, chains, or clusters 25 Chlorobi… • Have chlorosomes – ellipsoidal vesicles attached to plasma membrane – contain accessory photosynthetic pigments – most efficient light harvesting complexes found in nature 26 Chlorosomes –Green Sulfur & Green Non-sulfur 27 Chlorobi… • Lack flagella; nonmotile • Some have gas vesicles – used to adjust depth of cell for adequate light and H2S • Obligately anaerobic photolithoautotrophs – use H2S, elemental sulfur and H2 as electron sources – elemental sulfur deposited outside cell 28 Figure 21.5 29 Phylum Chloroflexi • Green nonsulfur bacteria • Contains photosynthetic and nonphotosynthetic members – e.g., genus Chloroflexus – photosynthetic – e.g., genus Herpetosiphon nonphotosynthetic 30 Genus Chloroflexus • Thermophilic – often isolated form neutral to alkaline hot springs – grow in form of orange-reddish mats • Metabolism – anoxygenic photosynthesis • does not use water as electron donor • photoheterotroph – can grow aerobically as a chemoheterotroph 31 Chloroflexus sp. 32 Chloronema sp. on stratified Michigan Lake Phylum Cyanobacteria • Largest, most diverse group of photosynthetic bacteria • Most obligate photolithoautotrophs; some can grow slowly in dark as chemoheterotrophs • One current classification system divides group into 62 species and 24 genera 33 Photosynthesis in cyanobacteria • Resembles that of eucaryotes – have chlorophyll a • prochlorophytes have chlorophyll a and b – have photosystem I and II – oxygenic photosynthesis 34 Photosynthesis in cyanobacteria… • Use phycobiliproteins as accessory pigments • phycobilisomes, which line thylakoid membranes, contain phycocyanin and phycoerythrin • prochlorophytes lack phycobilins • use Calvin cycle to fix CO2 35 Cyanobacterial Thylakoids and Phycobilisomes Figure 21.6 36 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. contains phycobilin pigments nitrogen storage polymer Figure 21.7 (a) 37 typical gramnegative cell wall site of photosynthesis Figure 21.7b 38 Oxygenic Photosynthetic Bacteria Figure 21.8 39 Heterocysts • Specialized cells used for nitrogen fixation – produced when organism is nitrogen deprived – differentiate from individual cells in filament • involves reorganization of photosynthetic membranes – thick heterocyst wall prevents O2 diffusion into heterocyst which would inactivate nitrogenase, enzyme responsible for nitrogen fixation 40 Heterocysts and Akinetes Figure 21.9 41 Prochlorophytes • Cyanobacteria in genera Prochloron, Prochlorococcus, and Prochlorothrix – distinguished by presence of chlorophyll a and b and lack of phycobilins • are the only procaryotes to possess chlorophyll b –makes them candidates as ancestors of endosymbionts that give rise to chloroplasts 42 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Prochloron Figure 21.10 43 Ecology of cyanobacteria • Tolerant of environmental extremes – thermophilic species can grow at temperatures up to 75°C – often are primary colonizers • Can cause blooms in nutrient-rich ponds and lakes – some produce toxins • Often form symbiotic relationships – e.g., are phototrophic partner in most lichens – e.g., symbionts with protozoa and fungi – e.g., nitrogen-fixing species form associations with plants 44 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Figure 21.11 45 Phylum Chlamydiae 46 Genus Chlamydia • Gram-negative bacteria – cell walls lack muramic acid and peptidoglycan – have very small genomes • Obligate intracellular parasites with unique developmental cycle – involving formation of elementary body (EB) and reticulate body (RB) or initial body – found mostly in mammals and birds – some recently isolated from spiders, clams, and freshwater invertebrates 47 Figure 21.13b 48 Chlamydial metabolism • Appear to be energy parasites, obtaining ATP from host – do have genes for substrate-level phosphorylation, electron transport, and oxidative phosphorylation • Reticulate bodies have biosynthetic capabilities when supplied precursors from host; can synthesize some amino acids • Elementary bodies seem to be dormant forms 49 Important pathogens • C. trachomatis – infects humans and mice – causes trachoma, nongonococcal urethritis, and other diseases in humans • C. psittaci – infects humans and many other animals – causes psittacosis in humans • C. pneumoniae – common cause of human pneumonia 50 Phylum Spirochaetes • Gram-negative bacteria with distinctive structure and motility – slender, long with flexible helical shape – creeping (crawling) motility due to a structure called an axial filament • Chemoheterotrophs • Ecologically diverse 51 Figure 21.14 52 axial filament = complex of axial fibrils (periplasmic flagella) Figure 21.15 (a1) and (a2) 53 Figure 21.15 (b) 54 Figure 21.15 (c) and (d) 55 Spirochete Motility current thought: axial fibrils rotate, causing corkscrew-shaped outer sheath to rotate and move cell through surrounding liquid Figure 21.16 56 Symbiotic Associations • Broad range of organisms • Found in a variety of locations, for example – hindguts of termites – digestive tracts of mollusks and mammals – oral cavities of animals 57 Spirochete-Protozoan Associations Figure 21.17 58 59