General features of Proteobacteria, alpha Proteobacteria
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5. 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
6. 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”
7. 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.
8. 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
9. 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
10. 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
11. 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)
12. 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.
13. Types of organisms
Purple Phototrophic Bacteria
Nitrifying Bacteria
Sulphur and Iron Oxidising Bacteria
Hydrogen Oxidising Bacteria
Methanotrophs
Acetic Acid Bacteria
Bioluminescent and Related Bacteria
14. 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
15. 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
16. 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
18. 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
19.
20. 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.
21. 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
24. Prevalent in the mud and water of lakes
and ponds with abundant organic matter
and low sulfide levels
25. 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
26. 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.
27. 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.
28. 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
29.
30.
31. 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
32. Bud is finally released as an oval- to
pear-shaped swarmer cell,
35. 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
36. 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
37.
38. 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
39. 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
40. 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
41. 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
43. 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
44. 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“
45. 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
46. 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
47. 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
48. owing largely to difficulties in cultivating
them
The Rickettsiales has a sister order
the Pelagibacterales
49. 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
50. 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
51. 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.