Chapter 15 (1)

Bacteria:The Proteobacteria

I. The Phylogeny of Bacteria

15.1 Phylogenetic 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

Major Genera of Proteobacteria

II. Phototrophs, Chemolithotrophs, and Methanotrophs

15.2 Purple Phototrophic Bacteria

15.3 The Nitrifying Bacteria

15.4 Sulfur- and Iron-Oxidizing Bacteria

15.5 Hydrogen-Oxidizing Bacteria

15.6 Methanotrophs and Methylotrophs

15.2 Purple Phototrophic Bacteria

Purple Phototrophic Bacteria

Carry out anoxygenic photosynthesis; no O2 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 (H2S) as an electron donor for

CO2 reduction in photosynthesis

Sulfide oxidized to elemental sulfur (So) that is stored

as globules either inside or outside cells

Sulfur later disappears as it is oxidized to sulfate (SO42-)

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 (S2O32-)

All are Gammaproteobacteria

Found in illuminated anoxic zones of lakes and other

aquatic habitats where H2S accumulates, as well as

sulfur springs

Genera and Characteristics of Purple Sulfur Bacteria

Genera and Characteristics of Purple Sulfur Bacteria

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 CO2 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 fulvum Rhodoblastus acidophilus Rhodobacter sphaeoides

Representatives of Purple Nonsulfur Bacteria

Rhodopila globiformis Rhodocyclus purpureus Rhodomicrobium vannielii

Genera and Characteristics of Purple Nonsulfur Bacteria

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 NH3 to NH2OH

Nitrite oxidase: oxidizes NO2- to NO3

-

* Hydroxylamine oxidoreductase

- oxidizes NH2OH to NO2-

- 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 (NH4+ + NO2

- → N2 + 2H2O)

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 (Fe2+)

Sulfur-Oxidizing Bacteria (cont’d)

Thiobacillus and close relatives are best studied

Rod-shaped

Sulfur compounds most commonly used as electron

donors are H2S, So, S2O32-; 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(CaCO3)

Sulfur-Oxidizing Bacteria (cont’d)

Beggiatoa

Filamentous, gliding bacteria

Found in habitats rich in H2S

e.g., sulfur springs, decaying seaweed beds, mud layers

of lakes, sewage polluted waters, and hydrothermal vents

Most grow mixotrophically

with 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 H2S with reduction of NO3- to

NH4+

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 H2 as sole electron

donor and O2 as electron acceptor (“knallgas” reaction)

Both gram-negative and gram-positive representatives

known

Contain one or more hydrogenase enzymes that

function to bind H2 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 CH4 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

C1 metabolism of methanotrophs

Methane monooxygenase

Incorporates an atom of oxygen from O2 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

15.10 Neisseria, Chromobacterium, and Relatives

15.11 Enteric Bacteria

15.12 Vibrio, Alivibrio, and Photobacterium

15.13 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 CaCO3 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 N2

aerobically

Genera of Free-Living Aerobic Nitrogen-Fixing Bacteria

Genera of Free-Living Aerobic Nitrogen-Fixing Bacteria

Genera of Free-Living Aerobic Nitrogen-Fixing Bacteria

The major genera of bacteria capable of fixing N2

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

O2

Azotobacter vinelandii

Vegitive cells Cysts

Examples of Slime Production by Nitrogen2-fixing Bacteria

Derxia gummosa

Examples of Slime Production by Nitrogen2-fixing Bacteria

Beijerinckia sp.

Additional genera of free-living N2 fixers include

acid-tolerant microbes

e.g., Beijerinckia and Derxia

Two Genera of Acid-Tolerant, Nitrogen2-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

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

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”