21 The Deinococci Mollicutes and Nonproteobacterial GramNegative Bacteria

21. 1 Aquificae and Thermotogae 1. Compare and contrast the physiological and structural differences between Aquificae and Thermotogae 2

• Volumes 1 and 5 of Bergey’s manual of systematic bacteriology Domain Bacteria • Deinococci and nonproteobacteria Gramnegatives – Gram-negative bacteria not belonging to phylum Proteobacterium • Characteristics include – morphology, reproduction, physiology, metabolism, and ecology 3

Aquificae • Aquificae – thought to be deepest (oldest) branch of Bacteria – contains one class, one order, and five genera • One of the best studied genera is Aquifex Bacterial thermophiles • optimum growth temperatures above 85°C 4

Genus Aquifex • Gram-negative rod • Thermophile – growth optimum 85°C - maximum 95°C • Microaerophilic • Chemolithoautotroph – uses hydrogen, thiosulfite, and sulfur as electron donor – uses oxygen as electron acceptor – genome ~1/3 size of E. coli 5

Phylum Thermotogae • Second deepest branch of Bacteria • Contains one class, one order, and six genera – best studied genus is Thermotoga 6

Genus Thermotoga • Gram-negative rods – outer sheathlike envelope balloons from ends of cell • Thermophiles (optimum 80°C; maximum 90°C) – grow in active geothermal areas • marine hydrothermal vents/terrestrial solfataric springs • Chemoheterotrophs – have functional glycolytic pathway – can grow anaerobically on carbohydrate/protein digests – ~24% of coding sequences similar to archaeal genes • may be due to horizontal gene transfer 7

21. 2 Deinococcus-Thermus 1. Explain why members of Deinococcus-Thermus have erroneously been considered Gram-positive 2. Describe habitats in which deinococci can be isolated 3. Discuss the unique capacity of the deinococci to tolerate dessication and high doses of radiation 8

Deinococcus-Thermus - 1 • Contains one class, Deinococci • Two orders, Deinococcales and Thermales • Three genera (genus Deinococcus is best studied) – 9 of 11 species are mesophilic; 2 are thermophilic • Spherical or rod-shaped; in pairs or tetrads – Gram-positive (lack typical Gram-positive cell wall) • layered outer membrane similar to Gram-negatives 9

Deinococcus-Thermus - 2 • Aerobic – catalase positive • 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 10

Deinococcus-Thermus - 3 • 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 – efficient proteins (protected by manganese) and enzymes for DNA repair • Within 12– 24 hours can repair chromosomes fragmented by exposure to radiation 11

21. 3 Class Mollicutes (Phylum Tenericutes) 12

Class Mollicutes (The Mycoplasmas) • Contains five orders and six families • Lack cell walls and are pleomorphic – smallest bacteria capable of self-reproduction 13

14

More about Mycoplasma • Genomes – less than 1000 genes – one of the smallest found in prokaryotes 15

Gliding Motility • Most nonmotile; some have gliding motility – 2 to 5 microns/second – self surface proteins surround “neck” of cell • attach to cytoskeletal proteins; function like microscopic legs • powered by ATP hydrolysis 16

Important Pathogens • Mycoplasma mycoides – pleuropneumonia in cattle • Mycoplasma gallisepticum – chronic respiratory disease in chickens • Mycoplasma hyopneumoniae – swine pneumonia • Mycoplasma pneumoniae – primary atypical pneumonia in humans • Ureaplasma urealyticum – premature birth, neonatal meningitis and pneumonia • spiroplasmas – pathogenic in insects, ticks, and a variety of plants 17

21. 4 Photosynthetic Bacteria - 1 1. Assess the importance of photosynthetic pigments in the distribution of photosynthetic bacteria in nature 2. Draw a generic chlorosome and identify the function of its structural elements 3. Predict the habitat closest to your home where you might find members of the phyla Chlorobi, Chloroflexi, and Cyanobacteria 4. Draw a generic cyanobacterial cell wall and label its intracellular structures 18

21. 4 Photosynthetic Bacteria - 2 5. List three types of specialized cells made by cyanobacteria and describe the function of each 6. Compare and contrast the prochlorophytes with other cyanobacteria 7. Draw a concept map describing the structure and physiology of the six types of photosynthetic bacteria listed in Table 21. 2 19

5 Phyla of Photosynthetic Bacteria • Phylum Chloroflexi – green nonsulfur bacteria • Phylum Chlorobi – green sulfur bacteria • Phylum Cyanobacteria 20

More Phyla… • Purple bacteria divided into 3 groups – purple sulfur • 2 g-proteobacterial families, Chromatiaceae and Ectothiorhodospiraceae – purple non-sulfur • distributed between a- and β-proteobacteria • Phylum Firmicutes – heliobacteria • Gram-negative thermophilic: Acidobacteria 21

Photosynthetic Bacteria • The cyanobacteria – carry out oxygenic photosynthesis • have two photosystems • use water as an electron donor and generate oxygen during photosynthesis – the purple and green bacteria carry out anoxygenic photosynthesis 22

23

Photosynthetic Microbes • Differences in photosynthetic pigments, with distinct absorption spectra, and oxygen requirements are important ecologically – inhabit different layers of water environments 24

Phylum Chlorobi • green sulfur bacteria • consists of one class, Chlorobia; one order, Chlorobiales; one family, Chlorobiaceae • representative genera are Chlorobium, Prosthecochloris, and Pelodictyon 25

• Green sulfur Bacteria – morphologically diverse – thrive in sulfide rich areas Phylum Chlorobi – have chlorosomes • ellipsoidal vesicles attached to plasma membrane • contain accessory photosynthetic pigments • Very efficient light harvesting complexes 26

Chlorobi… • Lack flagella; nonmotile • Some have gas vesicles – adjust depth of cell for light/H 2 S • Obligate anaerobic photolithoautotrophs – reaction center bacteriochlorophyll in plasma membrane – use H 2 S, elemental sulfur, and H 2 as electron sources – elemental sulfur deposited outside cell 27

Phylum Chloroflexi • Green nonsulfur bacteria • Has both photosynthetic and nonphotosynthetic members – e. g. , genus Chloroflexus – photosynthetic 28

Genus Chloroflexus • Filamentous – gliding motility • Thermophilic – often isolated from neutral to alkaline hot springs; grow in orange-reddish mats • Metabolism – anoxygenic photosynthesis • does not use water as electron donor • photoheterotroph – can grow aerobically as a chemoheterotroph 29

Phylum Cyanobacteria • Largest, most diverse group of photosynthetic bacteria – Chlorophyceae – blue green algae common term • Gram-negative • Many are obligate photolithoautotrophs; some can grow slowly in dark as chemoheterotrophs 30

Classification of Cyanobacteria • Bergey’s Manual divides into five subsections – major characteristics include morphology and reproductive patterns – other characteristics used • ultrastructure • genetic • physiology and biochemistry • habitat/ecology 31

32

Photosynthesis in Cyanobacteria • Resembles that of eukaryotes – have photosystems I and II – have chlorophyll a – oxygenic photosynthesis • one species performs anoxygenic photosynthesis using H 2 S as electron source 33

Photosynthesis in Cyanobacteria • Use phycobiliproteins as accessory pigments – phycobilisomes, which line thylakoid membranes, contain phycocyanin and phycoerythrin 34

More about Cyanobacteria • Range in diameter from ~1 to 10 mm • May be unicellular, colonial, or filaments called trichomes (a row of cells in close contact) 35

More about Cyanobacteria • Pigmentation – most appear blue-green due to presence of phycocyanin – presence of phycoerythrin in many ocean isolates gives them red or brown coloration – chromatic adaption • modulation of pigment concentrations in different light • Phototaxis by use of gas vacuoles 36

Specialized Reproductive Cells and Structures • Binary fission, budding, fragmentation, multiple fission • Hormogonia – small, motile fragments of filamentous cyanobacteria • Akinetes – dormant, thick-walled resting cells resistant to desiccation – often germinate to form new filaments • Baeocytes – produced by multiple fission – small spherical cells; escape when outer wall ruptures – some are motile by gliding motility 37

Heterocysts • Specialized cells used for nitrogen fixation – produced when organism is nitrogen deprived – differentiate from individual cells in filament – thick heterocyst wall prevents O 2 diffusion into heterocyst which would inactivate nitrogenase 38

Ecology of Cyanobacteria - 1 • 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 39

Ecology of Cyanobacteria - 2 • 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 plant associations 40

21. 5 Phylum Planctomycetes 1. Draw the unusual structural features of the planctomycetes 2. Identify the electron donor and acceptor used in the anammox reaction 3. Explain why the anammox reaction is important to the global flux of nitrogen 41

21. 6 Phylum Chlamydiae 1. Explain the term obligate intracellular parasite 2. Diagram the chlamydial life cycle 3. Deduce why chlamydia can survive despite significant metabolic limitations 42

Phylum Chlamydiae • Gram-negative • Obligate intracellular parasites – must grow and reproduce inside host cells – although known for ability to cause disease, many grow within hosts such as protists, and animal cells without adverse effects • One class, one order, four families, six genera – genus Chlamydia is best studied 43

Genus Chlamydia • Nonmotile, coccoid, Gram-negative – cell walls lack muramic acid, peptidoglycan – have very small genomes • Obligate intracellular parasites with unique developmental cycle 44

45

Chlamydial Metabolism • Cannot catabolize carbohydrates • Cannot synthesize ATP or NAD+ – import up from host – do have genes for substrate-level phosphorylation, electron transport, and oxidative phosphorylation • RBs have biosynthetic capabilities when supplied precursors from host; can synthesize some amino acids • EBs seem to be dormant forms 46

21. 7 Phylum Spirochaetes 1. Draw a spirochete cell as it would be observed in a scanning electron micrograph and in cross section by transmission electron microscopy 2. Describe how the unusual flagellar arrangement is well suited for motility in common spirochete habitats 47

Phylum Spirochaetes • Contains one class; one order, three families, 13 genera • Gram-negative, chemoheterotrophic bacteria with distinctive structure and motility – slender, long with flexible helical shape – creeping (crawling) motility due to a structure called an axial filament • Oxygen requirements vary 48

49

Spirochaetes Motility • Axial filament lies inside outer sheath – rotate, causing corkscrew-shaped outer sheath to rotate and move cell through surrounding liquid • Motility adapted to moving through viscous solutions 50

Symbiotic Associations between Spirochetes and Other Organisms • Ecologically diverse – free living – symbiotic • hindguts of termites • digestive tracts of mollusks and mammals • oral cavities of animals – disease • Lyme disease and syphilis are spirochete diseases 51

21. 8 Phylum Bacteroidetes 1. Explain how the human is host to members of this phylum 2. Describe the unusual carbon substrates used by some bacteroidetes 3. Explain the proposed mechanism for Flavobacterium johnsoniae gliding motility, and relate gliding motility to the microbe’s capacity to degrade complex organic substances 52

Phylum Bacteroidetes • Very diverse • Contains three classes – Bacteroides – Flavobacteria – Sphingobacteria • 12 families, and 63 genera 53

Class Bacteroides • Anaerobic, Gram-negative rods, various shapes – do not form endospores – motile or nonmotile • Chemoheterotrophs - fermentative • Often found in oral cavity and intestinal tract of humans and other animals and the rumen of ruminants – often benefit host by degrading complex carbohydrates, providing extra nutrition to host – constitute up to 30% of bacteria from human feces – some cause disease 54

Genus Cytophaga • Slender rods, often with pointed ends • Aerobic, degrade complex polysaccharides • e. g. , cellulose, chitin, pectin, keratin, agar • Play major role in mineralization of organic material – significant component of bacterial population in sewage treatment plants – most free-living; some pathogenic in vertebrates • e. g. , Cytophaga columnaris – pathogen of fish 55

Gliding Motility - 1 • Characteristic of phylum Bacteriodetes • Also present in many other taxa – fruiting and nonfruiting aerobic chemoheterotrophs – cyanobacteria – green nonsulfur bacteria – at least two Gram-positive genera 56

Gliding Motility - 2 • Gliding mechanism unknown – occurs when cells in contact with solid surface – cells leave slime trail; motility often lost with age – low-nutrient levels usually stimulate gliding 57

Advantages of Gliding Motility • Enables cells to encounter insoluble nutrient sources and digest them with cell bound digestive enzymes • Works well in drier habitats (e. g. , soil, sediments, and rotting wood) • Enables cells to position themselves optimally for light intensity, [O 2], [H 2 S], temperature, etc. 58