Chapter 15 (1) Bacteria: The Proteobacteria

I. The Phylogeny of Bacteria  15.1Phylogenetic Overview of Bacteria

Major Lineages (Phyla) of Bacteria

15.1 Phylogenetic Overview of Bacteria  Proteobacteria  A major lineage (phyla) of Bacteria  Includes many of the most commonly encountered bacteria  Most metabolically diverse of all Bacteria  e.g., chemolithotrophy, chemoorganotrophy, phototrophy  Morphologically diverse  Divided into five classes  Alpha-, Beta-, Delta-, Gamma-, Epsilon-

Major Genera of Proteobacteria

II. Phototrophs, Chemolithotrophs, and Methanotrophs  15.2Purple Phototrophic Bacteria  15.3The Nitrifying Bacteria  15.4Sulfur- and Iron-Oxidizing Bacteria  15.5Hydrogen-Oxidizing Bacteria  15.6Methanotrophs and Methylotrophs

15.2 Purple Phototrophic Bacteria  Purple Phototrophic Bacteria  Carry out anoxygenic photosynthesis; no O 2 evolved  Morphologically diverse group  Genera fall within the Alpha-, Beta-, or Gammaproteobacteria  Contain bacteriochlorophylls and carotenoid pigments  Produce intracytoplasmic photosynthetic membranes with varying morphologies - allow the bacteria to increase pigment content - originate from invaginations of cytoplasmic membrane

Liquid Cultures of Phototrophic Purple Bacteria Carotenoidless mutant Rhodospirillum rubrum Rhodobacter sphaeroides Lacks one of the carotenoids Rhodopila globiformis

Membrane Systems of Phototrophic Purple Bacteria Ectothiorhodospira mobilis Allochromatium vinosum

 Purple Sulfur Bacteria  Use hydrogen sulfide (H 2 S) as an electron donor for CO 2 reduction in photosynthesis  Sulfide oxidized to elemental sulfur (S o ) that is stored as globules either inside or outside cells  Sulfur later disappears as it is oxidized to sulfate (SO 4 2- )

Photomicrographs of Purple Sulfur Bacteria Chromatium okenii Thiospirillum jenense Thiopedia rosea Ectothiorhodospira mobilis

 Purple Sulfur Bacteria (cont’d)  Many can also use other reduced sulfur compounds, such as thiosulfate (S 2 O 3 2- )  All are Gammaproteobacteria  Found in illuminated anoxic zones of lakes and other aquatic habitats where H 2 S accumulates, as well as sulfur springs

Genera and Characteristics of Purple Sulfur Bacteria

Blooms of Purple Sulfur Bacteria Lamprocystis roseopersicina Algae (Spirogyra) Chromatium sp. Thiocystis sp.

 Purple Nonsulfur Bacteria  Originally thought organisms were unable to use sulfide as an electron donor for CO 2 reduction, now know most can  Most can grow aerobically in the dark as chemoorganotrophs  Some can also grow anaerobically in the dark using fermentative or anaerobic respiration  Most can grow photoheterotrophically using light as an energy source and organic compounds as a carbon source  All in Alpha- and Betaproteobacteria

Representatives of Purple Nonsulfur Bacteria Phaeospirillum fulvumRhodoblastus acidophilus Rhodobacter sphaeoides

Representatives of Purple Nonsulfur Bacteria Rhodopila globiformisRhodocyclus purpureus Rhodomicrobium vannielii

Genera and Characteristics of Purple Nonsulfur Bacteria

15.3 The Nitrifying Bacteria  Nitrifying Bacteria  Able to grow chemolithotrophically at the expense of reduced inorganic nitrogen compounds  Found in Alpha-, Beta-, Gamma-, and Deltaproteobacteria  Nitrification (oxidation of ammonia to nitrate) occurs as two separate reactions by different groups of bacteria  Ammonia oxidizers (nitrosifyers) (e.g., Nitrosococcus)  Nitrite oxidizer (e.g., Nitrobacter)

Photomicrographs of Nitrosifyer Nitrosococcus oceani Phase-contrast micrograph Electron micrograph

Photomicrographs of the Nitrifyer Nitrobacter winogradskyi Phase-contrast micrograph Electron micrograph

 Nitrifying Bacteria (cont’d)  Many species have internal membrane systems that house key enzymes in nitrification  Ammonia monooxygenase: oxidizes NH 3 to NH 2 OH  Nitrite oxidase: oxidizes NO 2 - to NO 3 - * Hydroxylamine oxidoreductase - oxidizes NH 2 OH to NO attached to the periplasmic face of cytoplasmic membrane

 Nitrifying Bacteria (cont’d)  Widespread in soil and water  Highest numbers in habitats with large amounts of ammonia  i.e., sites with extensive protein decomposition and sewage treatment facilities  Most are obligate chemolithotrophs and aerobes  One exception is anammox organisms, which oxidize ammonia anaerobically (NH NO 2 - → N 2 + 2H 2 O)

Characteristics of the Nitrifying Bacteria

15.4 Sulfur- and Iron-Oxidizing Bacteria  Sulfur-Oxidizing Bacteria  Grow chemolithotrophically on reduced sulfur compounds  Two broad classes  Neutrophiles  Acidophiles  Some acidophiles able to use ferrous iron (Fe 2+ )

 Sulfur-Oxidizing Bacteria (cont’d)  Thiobacillus and close relatives are best studied  Rod-shaped  Sulfur compounds most commonly used as electron donors are H 2 S, S o, S 2 O 3 2- ; generates sulfuric acid  Achromatium  Common in freshwater sediments  Spherical cells  Pylogenetically related to purple bacteria Chromatium

* Some obligate chemolithotrophs possess special structures that house Calvin cycle enyzmes (carboxysomes)

Nonfilamentous Sulfur Chemolithotrophs Halothiobacillus neapolitanus Achromatium sp. carboxysomes Elemental sulfur Calcium carbonate (CaCO 3 )

 Sulfur-Oxidizing Bacteria (cont’d)  Beggiatoa  Filamentous, gliding bacteria  Found in habitats rich in H 2 S  e.g., sulfur springs, decaying seaweed beds, mud layers of lakes, sewage polluted waters, and hydrothermal vents  Most grow mixotrophically  w ith reduced sulfur compounds as electron donors  and organic compounds as carbon sources ( ∵ lack Calvin cycle enzymes)

Filamentous Sulfur-Oxidizing Bacteria Beggiatoa sp.

 Sulfur-Oxidizing Bacteria (cont’d)  Thioploca  Large, filamentous sulfur-oxidizing bacteria that form cell bundles surrounded by a common sheath  Thick mats found on ocean floor off Chile and Peru  Couple anoxic oxidation of H 2 S with reduction of NO 3 - to NH 4 +

Cells of a Large Marine Thioploca Species Thioploca sp.

 Sulfur-Oxidizing Bacteria (cont’d)  Thiothrix  Filamentous sulfur-oxidizing bacteria in which filaments group together at their ends by a holdfast to form cellular arrangements called rosettes  Obligate aerobic mixotrophs

Thiothrix

Physiological Characteristics of Sulfur Oxidizers

15.5 Hydrogen-Oxidizing Bacteria  Hydrogen-Oxidizing Bacteria:  Most can grow autotrophically with H 2 as sole electron donor and O 2 as electron acceptor (“knallgas” reaction)  Both gram-negative and gram-positive representatives known  Contain one or more hydrogenase enzymes that function to bind H 2 and use it to either produce ATP or for reducing power for autotrophic growth

 Hydrogen-Oxidizing Bacteria (cont’d)  Most are facultative chemolithotrophs and can grow chemoorganotrophically  Some can grow on carbon monoxide (CO) as electron donor (carboxydotrophs; carboxydobacteria)

Hydrogen Bacteria Ralstonia eutropha

Characteristics of Common Hydrogen-Oxidizing Bacteria

15.6 Methanotrophs and Methylotrophs  Methylotrophs  Organisms that can grow using carbon compounds that lack C-C bonds  Most are also methanotrophs

 Methanotrophs  Use CH 4 and a few other one-carbon (C1) compounds as electron donors and source of carbon  Widespread in soil and water  Obligate aerobes  Morphologically diverse

Substrates Used by Methylotrophic Bacteria

 C 1 metabolism of methanotrophs  Methane monooxygenase  Incorporates an atom of oxygen from O 2 into methane to produce methanol  Methanotrophs contain large amounts of sterols

 Classification of methanotrophs  Two major groups  Type I  Type II  Contain extensive internal membrane systems for methane oxidation

Electron Micrographs of Methanotrophs Methylosinus sp. (type II) Methylococcus capsulatus (type I)

 Type I methanotrophs  Assimilate C1 compounds via the ribulose monophosphate cycle  Gammaproteobacteria  Membranes arranged as bundles of disc-shaped vesicles  Lack complete citric acid cycle  Obligate methylotrophs

 Type II methanotrophs  Assimilate C1 compounds via the serine pathway  Alphaproteobacteria  Paired membranes that run along periphery of cell

Some Characteristics of Methanotrophic Bacteria

 Ecolony and Isolation of Methanotrophs  Widespread in aquatic and terrestrial environments  Methane monooxygenase also oxidizes ammonia; competitive interaction between substrates  Certain marine mussels have symbiotic relationships with methanotrophs

Methanotrophic Symbionts of Marine Mussels

III. Aerobic and Facultatively Aerobic Chemoorganotrophs  15.7 Pseudomonas and the Pseudomonads  15.8 Acetic Acid Bacteria  15.9 Free-Living Aerobic Nitrogen-Fixing Bacteria  Neisseria, Chromobacterium, and Relatives  Enteric Bacteria  Vibrio, Alivibrio, and Photobacterium  Rickettsias

15.7 Pseudomonas and the Pseudomonads  All genera within the pseudomonad group are  Straight or curved rods with polar flagella  Chemoorganotrophs  Obligate aerobes

Typical Pseudomonad Colonies and Cell Morphology Burkholderia cepacia

Typical Pseudomonad Colonies and Cell Morphology Pseudomonas sp.

Characteristics of Pseudomonads

 Species of the genus Pseudomonas and related genera can be defined on the basis of phylogeny and physiological characteristics

Subgroups and Characteristics of Pseudomonads

 Pseudomonads  Nutritionally versatile  Ecologically important organisms in water and soil  Some species are pathogenic  Includes human opportunistic pathogens and plant pathogens

Pathogenic Pseudomonads

 Zymomonas  Genus of large, gram-negative rods that carry out vigorous fermentation of sugars to ethanol  Used in production of fermented beverages  Sugar metabolism: Entner-Doudoroff pathway

15.8 Acetic Acid Bacteria  Acetic Acid Bacteria  Organisms that carry out incomplete oxidation of alcohols and sugars  Leads to the accumulation of organic acids as end products  Motile rods  Aerobic  High tolerance to acidic conditions

Copyright © 2009 Pearson Education Inc., publishing as Pearson Benjamin Cummings  Acetic Acid Bacteria (cont’d)  Commonly found in alcoholic juices  Used in production of vinegar  Some can synthesize cellulose (Acetobacter xylinum)  Colonies can be identified on CaCO 3 agar plates containing ethanol  Acetobacter: peritrichously flagellated, overoxidizer Gluconobacter: polarly flagellated, underoxidized

Colonies of Acetobacter aceti on Calcium Carbonate Agar

15.9 Free-Living Aerobic Nitrogen-Fixing Bacteria  A variety of soil microbes are capable of fixing N 2 aerobically

Genera of Free-Living Aerobic Nitrogen-Fixing Bacteria

 The major genera of bacteria capable of fixing N 2 nonsymbiotically are Azotobacter, Azospirillium, and Beijerinckia  Azotobacter are large, obligately aerobic rods; can form resting structures (cysts)  All genera produce extensive capsules or slime layers; believed to be important in protecting nitrogenase from O 2

Azotobacter vinelandii Vegitive cells Cysts

Examples of Slime Production by Nitrogen 2 -fixing Bacteria Derxia gummosa

Examples of Slime Production by Nitrogen 2 -fixing Bacteria Beijerinckia sp.

 Additional genera of free-living N 2 fixers include acid-tolerant microbes  e.g., Beijerinckia and Derxia

Two Genera of Acid-Tolerant, Nitrogen 2 -fixing Bacteria Beijerinckia indica Derxia gummosa Contain a large globules of poly-β-hydroxybutyrate at each end

15.10 Neisseria, Chromobacterium, and Relatives  Neisseria, Chromobacterium, and their relatives can be isolated from animals, and some species of this group are pathogenic

Characteristics of the Genera of Gram-Negative Cocci

Chromobacterium and Neisseria Chromobacterium violaceum Violacein

Neisseria gonorrhoeae

15.11 Enteric Bacteria  Enteric Bacteria  Relatively homogeneous phylogenetic group within the Gammaproteobacteria  Facultative aerobes  Motile or non-motile, nonsporulating rods  Possess relatively simple nutritional requirements  Ferment sugars to a variety of end products

Defining Characteristics of the Enteric Bacteria

 Enteric bacteria can be separated into two broad groups by the type and proportion of fermentation products generated by anaerobic fermentation of glucose  Mixed-acid fermentators  2,3-butanediol fermentators

Enteric Fermentations

Butanediol-Producing Bacterium Erwinia carotovora

 Diagnostic tests and differential media are often used to identify various genera of enteric bacteria

Key Diagnostic Reactions Used to Separate Enteric Bacteria

A Simple Key to the Main Genera of Enteric Bacteria

 Escherichia  Universal inhabitants of intestinal tract of humans and warm-blooded animals  Synthesize vitamins for host  Some strains are pathogenic (O157:H7)

 Salmonella and Shigella  Closely related to Escherichia  Usually pathogenic  Salmonella characterized immunologically by surface antigens

 Proteus  Genus containing rapidly motile cells; capable of swarming  Frequent cause of urinary tract infections in humans

Swarming in Proteus Proteus mirabilis with as bundle of peritrichous flagella

A swarming concentric colony of Proteus mirabilis

 Butanediol fermentators are a closely related group of organisms  Some capable of pigment production

Reactions Used to Separate 2,3-Butanediol Producers

Colonies of Serretia marcescens Red-orange pigmentation of Serratia marcescens due to the pyrrole-containing “prodigiosin”