1 Chapter 22 Bacteria: The Proteobacteria

2 The phylum Proteobacteria The largest phylogenetically coherent bacterial group with over 2,000 species assigned to more than 500 genera

3 Phylogenetic Relationships Among the Procaryotes Figure 22.1

4 Phylogenetic Relationships Among Major Groups Within the  -Proteobacteria Figure 22.2

5 The Purple Nonsulfur Bacteria

6 Purple nonsulfur bacteria… Metabolically flexible –normally grow anaerobically as anoxygenic photoorganoheterotrophs possess bacteriochlorophylls a or b in 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

7 Purple nonsulfur bacteria… Found in mud and water of lakes and ponds with abundant organic matter and low sulfide levels; some marine species Many genera can produce cellular cysts –resting cells –resistant to desiccation but less tolerant of heat and UV than bacterial endspores –made in response to nutrient limitation –have thick outer coat and store polyhydroxybutyrate

8 Figure 22.3

9 Rickettsia and Coxiella Genus Rickettsia –class Alphaproteobacteria; order Rickettsiales; family Rickettsiaceae Genus Coxiella –class Gammaproteobacteria; order Legionellales; family Coxiellaceae These are considered together because of important similarities

10 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  m Coxiella – 0.2 to 0.4 by 0.4 to 1.0  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

11 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

12 human fibroblast filled with Rickettsia prowazekii Figure 22.4 (a)

13 Figure 22.4 (c) Coxiella burnetti growing within fibroblast vacuole

14 Rickettsia metabolism Lack glycolytic pathway –do not use glucose as energy source Oxidize glutamate and TCA cycle intermediates (e.g., succinate) Take up and use ATP and other materials from host cell

15 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

16 Genus Rhizobium Gram-negative, motile rods –often contain poly-  -hydroxybutyrate granules –become pleomorphic under adverse conditions Grow symbiotically as nitrogen- fixing bacteroids within root nodule cells of legumes

17 Figure 22.9

18 Genus Agrobacterium Do not stimulate nodule formation or fix nitrogen Invade crown, roots, and stems of many plants –transform infected plant cells into autonomously proliferating tumors e.g., Agrobacterium tumefaciens –causes crown gall disease by means of tumor-inducing (Ti) plasmid

19 Figure 22.10

20 Nitrifying Bacteria Divided into several taxa –class Alphaproteobacteria; family Bradyrhizobiaceae – e.g., genus Nitrobacter –class Betaproteobacteria; family Nitrosomonadaceae – e.g., genera Nitrosomonas and Nitrosospira –class Gammaproteobacteria family Ectothiorhodospiraceae – e.g., genus Nitrococcus family Chromatiaceae – e.g., genus Nitrosococcus

21 Table 22.2

22 Figure 22.11

23 Nitrification ammonia  nitrite  nitrate conversion of ammonia to nitrate by action of two genera –e.g., Nitrosomonas – ammonia to nitrite –e.g., Nitrobacter – nitrite to nitrate Fate of nitrate – easily used by plants –lost from soil through leaching or denitrification

24 Phylogenetic Relationships Among Major Groups Within the  -Proteobacteria Figure 22.12

25 Table 22.3

26 Order Neisseriales

27 Genus Neisseria Inhabitants of mucous membranes of mammals –some human pathogens Neisseria gonorrhoeae – gonorrhea Neisseria meningitidis - meningitis

28 Order Burkholderiales Contains four families, three with well-known genera –genus Burkholderia in family Burkholderiaceae –genus Bordetella in family Alcaliginaceae –genera Sphaerotilus and Leptothrix in family Comamonadaceae

29 Genus Burkholderia Gram-negative, non–spore-forming, straight rods –most motile with single flagellum or tuft of polar flagella aerobic and mesophilic nonfermentative chemoorganotrophs –catalase positive; often oxidase positive –most use poly-  -hydroxybutyrate as carbon reserve

30 e.g., Burkholderia cepacia degrades > 100 organic molecules –very active in recycling organic material plant pathogen has become a major nosocomial pathogen –particular problem for cystic fibrosis patients

31 Nitrogen Fixation by Burkholderia and Ralstonia Both genera form symbiotic associations with legumes similar to that formed by rhizobia Both genera have nodulation genes (nod) similar to rhizobia suggesting a common genetic origin –genetic information may have been obtained through lateral gene transfer

32 Order Nitrosomonadales Contains a number of chemolithotrophs –two genera of nitrifying bacteria Nitrosomonas and Nitrosospira –genus Gallionella stalked bacterium –genus Spirillum (in family Spirillaceae)

33 Figure 22.15

34 Order Hydrogenophilales contains genus Thiobacillus –well studied chemolithotroph –prominent member of colorless sulfur bacteria chemolithotrophs that oxidize sulfur compounds other colorless sulfur bacteria are in class Gamma proteobacteria

35 Genus Thiobacillus found in soil and aquatic habitats –production of sulfuric acid can cause corrosion of concrete and metal structures –may increase soil fertility by releasing sulfate –used in leaching metals from low grade metal ores

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 36 Figure 22.16

37 Phylogenetic Relationships Among  Proteobacteria largest subgroup of proteobacteria contains 14 orders, and 25 families Figure (a)

38 Figure (b)

39 The Purple Sulfur Bacteria placed in order Chromatiales –divided into two families, Chromatiaceae and Ectothiorhodospiraceae –Family Ectothiorhodospiraceae contains eight genera

40 Figure 22.18

41 Family Chromatiaceae typical purple sulfur bacteria strict anaerobes usually photoautolithotrophs –use H 2 S as electron donor deposit sulfur granules internally often eventually oxidize sulfur to sulfate –may also use hydrogen as electron donor usually found in anaerobic, sulfide-rich zones of lakes –can cause large blooms in bogs and lagoons e.g., genera Thiospirillum, Thiocapsa, and Chromatium

42 Figure 22.19

43 Figure (a)

44 Order Methylococcales contains family Methylococcaceae; seven genera morphologically diverse –e.g., genus Methylococcus – spherical, nonmotile –e.g., genus Methylomonas – straight, curved, or branched rods with single polar flagella –almost all form resting stage (cystlike structure) methylotrophs –use reduced one-carbon compounds as sole carbon and energy source

45 Methane oxidation occurs in complex arrays of intracellular membranes oxidized to methanol and then to formaldehyde –electrons donated to electron transport chain for ATP synthesis –formaldehyde can be assimilated into cell material

46 Order Pseudomonadales contains family Pseudomonadaceae; 15 genera –Pseudomonas is the most important genus in the order Pseudomonadales gram-negative straight or slightly curved rods 0.5 to 1.0  m by 1.5 to 5.0  m in length motile by one or several polar flagella lack prosthecae or sheaths

47 Pseudomonas chemoheterotrophs with respiratory metabolism –usually use oxygen as electron acceptor –sometimes use nitrate as electron acceptor –have functional TCA cycle –most hexoses are degraded by Entner- Doudoroff pathway

48 Practical importance of pseudomonads metabolically versatile –degrade wide variety of organic molecules –mineralization microbial breakdown of organic materials to inorganic substrates important experimental subjects some are major animal and plant pathogens some cause spoilage of refrigerated food –can grow at 4°C

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 49 Figure 22.24

50 Figure 22.25

51 Order Enterobacteriales contains one family, Enterobacteriaceae; over 44 genera –referred to as enterobacteria or enteric bacteria (enterobacteria) facultative anaerobes chemoorganotrophs that degrade sugars by glycolytic pathway –can cleave pyruvate to yield formic acid (formic acid fermentation)

52 Figure 22.29

53 Table 22.7

54 Table 22.7 (continued)

55 Escherichia coli Probably best studied bacterium inhabitant of intestinal tracts of many animals Used as indicator organisms for testing water for fecal contamination Some strains are pathogenic –gastroenteritis –urinary tract infections

56 Important pathogenic enteric bacteria Salmonella – typhoid fever and gastroenteritis Shigella – bacillary dysentery Klebsiella – pneumonia Yersinia - plague Erwinia – blights, wilts, etc., of crop plants

57 Figure 22.30

58 Order Pasteurellales contains one family, Pasteurellaceae; six genera

59 Important pathogens Pasteurella multiocida – fowl cholera Pasteurella haemolytica – pneumonia in cattle, sheep and goats Haemophilus influenzae – variety of diseases, including meningitis in children

60 Class Deltaproteobacteria contains eight orders and 20 families –divided into two general groups aerobic, chemoorganotrophic predators anaerobic, chemoorganotrophic sulfur- and sulfate-reducers

61 Figure 22.31

62

63 Orders Desulfovibrionales, Desulfobacterales, and Desulfuromonadales Strict anaerobes Sulfur- or sulfate-reducing bacteria –use sulfur and sulfate as electron acceptors during anaerobic respiration –electron transport chain used to generate ATP Widespread in muds and sediments of aquatic environments, including sewage treatment systems –important in sulfur cycling

64 Figure 22.32

65 Order Bdellovibrionales –best studied is Bdellovibrio predatory bacteria

66 Bdellovibrio bactivorus Figure 22.23

67 Figure (a)

68 Epsilon Proteobacteria Smallest of proteobacterial classes Consists of one order, Campylobacteriales; three families

69 Figure 22.38

70 Genus Campylobacter Contains both pathogenic and nonpathogenic species –Campylobacter fetus reproductive disease and abortions in cattle and sheep septicemia and enteritis in humans –septicemia – pathogens or their toxins in blood –enteritis – inflammation of intestinal tract –Campylobacter jejuni abortions in sheep enteritis diarrhea in humans

71 Genus Helicobacter At least 14 species isolated from stomachs and upper intestines of humans, dogs, cats, and other mammals e.g., Helicobacter pylori –causes gastritis and peptic ulcer disease –produces large quantities of urease urea hydrolysis appears to be associated with virulence