Proteobacteria

Proteobacteria
Prepared by
Dharmesh N. Sherathia
CCSIT, Junagadh(BKNMU)
dharmesh.microbio@gmail.com

 The Proteobacteria are a major group
(phylum) of bacteria
 Include a wide variety of pathogens, such as
Escherichia, Salmonella, Vibrio, Helicobacter,
and many other notable genera
 Proteobacteria are Gram-negative, with an
outer membrane mainly composed of
lipopolysaccharides
 move about using flagella, but some are
nonmotile or rely on bacterial gliding
 The last include the myxobacteria

 many different shapes, to reflect the
enormous diversity of morphologies and
physiologies observed within this bacterial
phylum
 In 2002, the Proteobacteria consist of more
than 460 genera and more than 1600
species, scattered over 5 major
phylogenetic lines of descent known as the
classes
 “Alphaproteobacteria,”
 “Betaproteobacteria,”
 “Gammaproteobacteria,”
 “Deltaproteobacteria”

Habitat
 Organisms that can be found in different
habitats ranging from plant roots
(Rhizobium and Azospirillum) inside the
cells of a host (rickettsias) and as free living
bacteria in the environment such as
Methylobacteriaum species
 Found in virtually any environment across
the globe
 Some of the species in the phyla can
survive extreme environments with very
little to no oxygen.

 Diversity of morphological and
physiological types: besides rods and cocci,
curved, spiral, ring-shaped, appendaged,
filamentous and sheathed bacteria occur
among this phylum
 Most Proteobacteria are
mesophilicphilic,but some thermophilic
(e.g., Thiomonas thermosulfata and
Tepidomonas) and psychrophilic (e.g.,
Polaromonas) representatives have been
described

 A great number of Proteobacteria are
motile by means of polar or peritrichous
flagella, whereas the myxobacteria
(belonging to the “Deltaproteobacteria”)
display a gliding type of motility and show
highly complex developmental lifestyles,
whereby often remarkable multicellular
and macroscopic structures (so-called
“fruiting bodies”) are formed

 Most of the known Proteobacteria are
free-living; some (such as the rhizobia)
enter in symbiotic associations with
specific leguminous plants, where they fix
nitrogen in root or stem nodules
 Others live as intracellular endosymbionts
of protozoa and invertebrates (mussels,
insects and nematodes), whereas the
rickettsiae are obligate intracellular
parasites of humans or mammals

 The extreme diversity of energy generating
mechanisms is a unique biochemical
characteristic of the Proteobacteria: some
are chemoorganotrophs (e.g., Escherichia
coli), others are chemolithotrophs (e.g., the
sulfuroxidizing bacteria such as the
thiobacilli and the ammonia-oxidizing
bacteria such as Nitrosomonas) or
phototrophs (e.g., the purple colored
Chromatium, Rhodospirillum and many
others)

 Concerning their relationship towards
oxygen, the Proteobacteria include strictly
aerobic and anaerobic species as well as
facultative aerobes and microaerophiles
 Denitrifiers are reported among the
“Alphaproteobacteria,”
“Betaproteobacteria,”
“Gammaproteobacteria,” and the
“Epsilonproteobacteria.

Types of organisms
 Purple Phototrophic Bacteria
 Nitrifying Bacteria
 Sulphur and Iron Oxidising Bacteria
 Hydrogen Oxidising Bacteria
 Methanotrophs
 Acetic Acid Bacteria
 Bioluminescent and Related Bacteria

Classification
 1987, Carl Woese established-
ribosomal RNA (rRNA) sequences
 The Proteobacteria are divided into six
sections, referred to by the Greek letters
alpha through zeta
 alpha, beta, delta, epsilon sections are
monophyletic.
 Alphaproteobacteria, Betaproteobacteria,
Gammaproteobacteria,
Deltaproteobacteria, Epsilonproteobacteria
and Zetaproteobacteria

HISTORY
 1987, Carl Woese established this grouping
called it the "purple bacteria and their
relatives“
 great diversity of forms found in this group
 Proteobacteria are named after Proteus
 Greek god of the sea
 Capable of assuming many different
shapes, and it is therefore not named after
the genus Proteus

 Great biological importance, as they
include the majority of the known Gram
negatives of medical, veterinary, industrial
and agricultural interest
 Because they play key roles in the carbon,
sulfur and nitrogen cycles on our planet
e.g rhizobium, green purple sulphur
bacteria

 Oligotrophic proteobacteria- those capable of
growing at low nutrient levels
 Some have unusual metabolic modes such as
Methylotrophy (Methylobacterium),
 Chemolithotrophy (Nitrobacter)
 fix nitrogen (Rhizobium)
 Members of genera such as Rickettsia and Brucella
are important pathogens
 Many genera are characterized by distinctive
morphology such as prosthecae

 A prostheca (pl., prosthecae) is an
extension of the cell, including the
plasma membrane and cell wall, that
is narrower than the mature cell
 A stalk is a nonliving appendage
produced by the cell and extending
from it.
 Budding is distinctly different from
the binary fission normally used by
bacteria.

The Purple Non sulfur Bacteria
 Noxygenic photosynthesis, possess
bacteriochlorophylls a or b,
 All purple nonsulfur bacteria are –
proteobacteria (exception Rhodocyclus)
 Trap light energy and employ organic
molecules as both electron and carbon
sources(photoorganoheterotrophs)-
Nonsulfur Bacteria(do not oxidize
elemental sulfur to sulfate)
 During absence of light- devoid colour-
grow like chemoorganotrophs

Representatives of Purple Nonsulfur Bacteria
Figure 15.6

 Prevalent in the mud and water of lakes
and ponds with abundant organic matter
and low sulfide levels

Family: Rhodospirillaceae
 Rhodospirillum and Azospirillum
 Cyst formation is unique feature of this
family
 Cyst is for
1. Protect cell from dessication
2. Less protective against UV and heat
3. Made in response to nutrient limitations

Rickettsia and Coxiella
 These bacteria are rod-shaped, coccoid, or
pleomorphic with typical gram-negative
walls and no flagella.
 Although their size varies, they tend to be
very small. For example, Rickettsia is 0.3 to
0.5 m in diameter and 0.8 to 2.0 m long; .
All species are parasitic or mutualistic.

 The parasitic forms grow in vertebrate
erythrocytes, macrophages , and vascular
endothelial cells.
 Often they also live in blood-sucking
arthropods such as fleas, ticks, mites, or lice,
which serve as vectors or primary hosts.
 This order contains many important
pathogens.
 Rickettsia prowazekii and R. typhi are
associated with typhus fever, and R. rickettsii,
with Rocky Mountain spotted fever.
 Coxiella burnetii causes Q fever in humans.

 Rickettsias are very different from most
other
 They lack glycolytic pathways and do not
use glucose as an energy source, but
rather oxidize glutamate
 The rickettsial plasma membrane has
carrier-mediated transport systems
 host cell nutrients and coenzymes are
absorbed and directly used

The Caulobacteraceae and
Hyphomicrobiaceae
 These bacteria can have at least one of three
different features: a prostheca, a stalk, or
reproduction by budding
 The genus Hyphomicrobium contains
chemoheterotrophic, aerobic, budding bacteria
that frequently attach to solid objects in
freshwater, marine, and terrestrial
environments
 About 0.5 to 1.0 by 1 to 3 m- vegetative cell
size
 Prostheca 0.2 to 0.3 um in diameter, that
grows to several um in length

 Bud is finally released as an oval- to
 pear-shaped swarmer cell,

 Distinct metabolism -> Sugars and most
amino acids do not support abundant
growth
 https://www.tandfonline.com/doi/pdf/10.1
080/00021369.1982.10865468
 Hyphomicrobium grows on ethanol and
acetate and flourishes with one-carbon
compounds such as methanol, formate,
and formaldehyde
 facultative methylotroph and can derive
both energy and carbon from reduced one
carbon compounds
 Hyphomicrobium may comprise up to 25%
of the total bacterial population in

Caulobacter
 Possess a prostheca and holdfast
 Material secreted at the end of the
Caulobacter holdfast is the strongest biological
adhesion molecule known-superglue
 Freshwater and marine habitats with low
nutrient levels
 Adhere to bacteria, and got nutrient from
them
 Here prostheca contain only cytoplasm of cell
can enlarge 10 time larger than vegetative cells
 Caulobacter can survive in diluted medium by
enlarging their size

Family:Rhizobiaceae
 Order Rhizobiales of the -proteobacteria
contains 11 families
 This includes the family Hyphomicrobiaceae
 Important family in this order is Rhizobiaceae
which includes rhizobium and agrobacterium
 Cells often contain poly—hydroxybutyrate
inclusions. They grow symbiotically within root
nodule cells of legumes as nitrogen-fixing
bacteroids
 Live with leguminous plant symbiotically within
the nodule it fix atmospheric nitrogen

 Agrobacterium is placed in the family
Rhizobiaceae but differs from Rhizobium
 agrobacteria invade the crown, roots, and
stems of many plants and transform plant cells
into autonomously proliferating tumor cells
 Responsible genes are located on plasmid
 best-studied species is A. tumefaciens, which
enters many broad-leaved plants through
wounds and causes crown gall disease
 Presence of a large Ti (for tumor inducing)
plasmid

Nitrifying Bacteria
 Nitrifiers may be rod-shaped, ellipsoidal,
spherical, spirillar or lobate, and they may
possess either polar or peritrichous flagella
 Nitrifying bacteria make important
contributions to the nitrogen cycle

 most of the proteobacteria that are
capable of growth at very low levels of
nutrients
 Some have unusual morphology, including
protrusions such as stalks or buds known
as prosthecae.
 also include agriculturally important
bacteria capable of inducing nitrogen
fixation in symbiosis with plants, and
several plant and human pathogens

List of microbes included in alpha
proteobacteria

Magnetococcus marinus
 ability to form a structure called a
magnetosome
 a membrane encased single-magnetic-
domain mineral crystals formed by
biomineralisation
 allows the cells to orientate along the
Earth’s geomagnetic field

 Magnetotactic bacteria (or MTB) are a
polyphyletic group of bacteria discovered
by Richard P. Blakemore in 1975
 The biological phenomenon of
microorganisms tending to move in
response to the environment's magnetic
characteristics is known as magnetotaxis
 Blakemore realised that these
microorganisms were following the
direction of Earth's magnetic field, from
south to north, and thus coined the term
"magnetotactic“

 The MTBs can be subdivided into two
categories, according to whether they
produce particles of magnetite (Fe3O4) or
of greigite (Fe3S4)
 Many MTB are able to survive only in
environments with very limited oxygen,
and some can exist only in completely
anaerobic environments

 Some types of magnetotactic bacteria can
produce magnetite even
in anaerobic conditions, using nitric
oxide, nitrate, or sulfate as a final acceptor
for electrons. The greigite mineralising
MTBs are usually strictly anaerobic
 It has been suggested MTB evolved in the
early Proterozoic Era

order: Rickettsiales
 Most of those described survive only
as endosymbionts of other cells
 Some are notable pathogens,
including Rickettsia, which causes a
variety of diseases in humans
 Studies support the endosymbiotic
theory according to
which mitochondria and
related organelles developed from
members of this group

 owing largely to difficulties in cultivating
them
 The Rickettsiales has a sister order
the Pelagibacterales

Order: Pelagibacterales
 Alphaproteobacteria composed of free-
living bacteria
 It was first placed in the Rickettsiales, but
was later raised to the rank of order, and
then placed as sister order to
the Rickettsiales
 Pelagibacter ubique and related species
are oligotrophs—scavengers—and feed on
dissolved organic carbon and nitrogen

 They are unable to fix carbon or nitrogen,
but can perform the TCA
cycle with glyoxylate bypass and are able
to synthesise all amino-acids, except
glycine
 It is non-photosynthetic
 Possesses proteorhodopsin (incl. retinol bi
osynthesis) for ATP production from light

Parvularcula bermudensis
 Parvularcula isolates are Gram-negative,
strictly aerobic, chemoheterotrophic,
slightly motile short rods with a
single flagellum.
 Colonies on marine agar are very small
(0·3–0·8 mm in diameter), yellowish-brown
and very hard. They are oxidase positive
and catalase negative.

Proteobacteria

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