MAJOR
GROUPS OF
BACTERIA

 BACTERIA are microscopic, unicellular,
prokaryotic organisms.
 They lack memberane bound nucleus and
memberane bound
organelles.

 Bacteria are classified into two major groups-
1)ARCHAEBACTERIA(Primitive)
2)EUBACTERIA(True bacteria)

ARCHAEBACTERIA
 Oldest living organism
 Classified as bacteria
 As they look bacteria
 They have features that are quite different,
however, from both bacteria and eukaryotic
organisms.
 Carl Woese – 3 domain system.
 Woese proposed archaebacteria archae.

 Archae are similar to eukaryotic organisms in that
 they lack a part of the cell wall called the
peptidoglycan.
 Similarity in the way by which they make new
copies of their genetic material
 archae are similar to bacteria in that
 their genetic material is not confined within a
membrane, but instead is spread throughout the
cell.
 Thus, archae represent a blend of bacteria and
eukaryotes “missing link”, although generally they
are more like eukaryotes than bacteria.

 Obligate anaerobes.
 Cell is with thick cytoplasm and rigid cell wall.
 Cell wall made up of Pseudomurein,
 a combination of N-acetyltalosaminuronic acid and N-
acetylglucosamine.
 It gives immunity to lysozyme.
 Found in extreme environmental conditions.
 extremophiles
 Reproduction by binary fission.
You can refer:
 https://www.vedantu.com/biology/archaebacteria
 https://ucmp.berkeley.edu/archaea/archaea.html

 Includes 2 distinct groups:
➢ Methanogens
➢ Extremophiles:
• Halophiles
• Thermophiles
• Acidophiles
• Alkaliphiles

METHANOGENS

METHANOGENS
 Group of archaebacteria that produce methane as a
byproduct in anoxic conditions (methanogenesis)
 Found in wetlands, marshy areas, digestive tract of animals etc.
 Coccoid or rod shaped.
 Cell wall devoid of peptidoglycan.

 Strictly obligate anaerobes.
 Use anaerobic respiration for ATP synthesis.
 Sensitive to oxygen, cannot tolerate oxygen stress for
prolonged time.
 Thrive in environments in which all electron acceptors other
than CO2 have been depleted.

Methanococcus Methanopyrus
Methanobacterium bryantii

 Examples for Methanogens:
❑Methanobacterium bryantii
❑Methanococcus spp.
❑Methanobrevibacter spp.
❑Methanocorpusculum spp.
❑Methanospirillum hungatei
❑Methanothermobacter thermoflexus
❑Methanothrix sochngenii

EXTREMOPHILES

EXTREMOPHILES
 Organism that thrives under ‘extreme’ environmental
conditions under high pressure and high temperature.
 Habitats include volcanoes, hydrothermal vents, hot
springs, high saline lakes, acidic and sulphur containing
regions
 Unique enzyme EXTREMOZYMES are present.

 Various types of extremophiles:
1)THERMOPHILES
2)HALOPHILES
3)ACIDOPHILES
4)ALKALIPHILES

THERMOPHILES

THERMOPHILES
 Group of extremophilic organisms that thrives at
relatively high temperatures, between 41C and 122C
 Found in geothermal heated regions of earth-hot springs,
deep sea hydrothermal vents, decaying plant matter (peat
bogs, compost)
 Contain enzymes that can function at high temperature.
 Heat stable polymerase for PCR(taq polymerase enzyme)
obtained from Thermus aquaticus.

 Gram negative and anaerobic.
 Obligate and Facultative thermophiles.
 Obligate thermophiles(extreme thermophiles) require high
temperature for growth(above 80)
 Facultative(moderate thermophiles) can thrive high
temperature and also low temperature(below 50)
 Optimum growth temperature 50 or more,upto 70 or
more.
 Required reduced sulphur compounds for growth.
 Can grow lithotrophically with H2 as energy source.

Bright colors produced by thermophiles in the
hot springs ofYellow Stone National Park, USA

 Examples for thermophiles:
❑Sulfobus sulfataricus
❑Sulfobus acidocaldarius
❑Thermoproteus spp
❑Pyrobaculum spp
❑Pyrodictum spp
❑Thermococcus spp
❑Archeoglobus spp
❑Acidianus spp

HALOPHILES

HALOPHILES(Halobacteria)
 Group of extremophiles that thrive in high salt
concentrations.
 Found anywhere with a concentration of salt five times
greater than that of the ocean.
 (Great Salt Lake in Utah,
 Owens Lake in California,
 Dead Sea,evaporation ponds,etc)
 Slight,moderate and extreme halophiles.
 Slight halophiles: salt concentration between 0.3-0.8M
 Moderate halophiles: 0.8-3.4M
 Extreme halophiles: 3.4-5.1M

 Gram negative and aerobic or anaerobic
 Cell walls with complex heteropolysaccharide, gives
stability even at low salt concentration.
 Photoreceptor pigment BACTERIORHODOPSIN is
responsible for their photoproduction of energy.
 Some species give off a red color because of the
carotenoid compounds in bacteriorhodopsin.
 This gives pinkish color to the water bodies often called as
Pink Salt Lakes.

Dunaliellia salina
Chromohalobacter salexigens

Halococcus

 Examples for Halophiles:
❑Halococcus
❑Haloferax
❑Chromohalobacter salexigens
❑Halogeometricum
❑Dunaliella salina(halophile alga)
❑Wallemia ichthyophaga(halophile fungus)

ACIDOPHILES

ACIDOPHILES(Acidophilic bacteria)
 Group of extremophiles that can survive under high
acidic environments (pH 2.0 or below)
 Found in sulfur hot springs, volcanic sites, debris in coal
mines, stomachs of human, etc.
 Have efficient mechanism to pump protons out of the
intracellular space in order to keep the cytoplasm at or
near neutral pH
 The release of protective coatings on the outside of its
cell protect them from damage in acidic medium.

Acidic mud pond

 Some acidophiles helps in controlling the Acid Mine
Drainage (AMD).
 AMD is the outflow of acidic water from metal mines or
coal mines.
Acid Mine Drainage

 Acidophiles helps to catalyse the acidic liquids and other
pollutants in the AMD and thus economically important.
 Acidophiles in AMD are
➢Leptospirillum ferooxidans
➢Acidithiobacillus thiooxidans
➢Sulfobacillus themosulfidooxidans

 Rocks with abundant sulfide minerals causes Acid Rock
Drainage.(ARD)
 It is natural as a part of weathering. But becomes
abnormal when earth is disturbed.(construction
works,mining)

Acid stained rocks

Acid Rock Drainage

 Other acidophiles are
➢Acidianus
➢Halarchaeum acidiphilum
➢Metallosphaera sedula
➢Thiobacillus spp
➢Dunaliella acidophila etc.

ALKALIPHILES

ALKALIPHILES
 Group of extremophiles capable of survival in alkaline
environments(pH 8.5-11),growing optimally around pH 10.
 - obligate alkaliphiles, facultative alkaliphiles and
haloalkaliphiles.
 Obligate alkaliphiles require high pH.
 Facultative alkaliphiles survive both in high and normal pH.
 Haloalkaliphiles require high salt content.

 Cystolic acidification.
 Cell walls contain acidic polymers composed of
galacturonic acid,gluconic acid,glutamic acid,aspartic
acid,phosphoric acid etc.
 This forms an acidic matrix that helps the plasma
membarane from alkaline conditions by preventing
the entry of OH- and allowing the uptake of Na+ and
H+ ions.

 Alkaliphilic enzymes such as proteases,starch
degrading enzymes,lipases,pectinases etc are
obtained;economically important.
 Examples for alkaliphiles:
❑Halorhodospira halochloris
❑Natronomonas pharaonis
❑Thiohalospira alkaliphila
❑Microcystis spp

EUBACTERIA
 True bacteria.
 Composed of bacteria of a large group typically having
simple cells with rigid cell wall and often with flagella for
movement.
 Include Gram positive and Gram negative bacteria.
 Present everywhere.(soil ,water, on organisms etc)

MAJOR GROUPS OF EUBACTERIA
 Rickettsias
 Spirochates
 Chlamydias
 Mycoplasmas
 Actinomycetes
 Myxobacteria

RICKETTSIAS

Rickettsia
 Are non-motile, Gram-negative, non-
sporeforming, highly pleomorphic bacteria that
can present as cocci (0.1 μm in diameter), rods
(1–4 μm long) or thread-like (10 μm long).
 Obligate intracellular parasites
 Rickettsiae comprise a group of microorganisms
that phylogenetically occupy a position between
bacteria and viruses.
 The genus Rickettsia is included in the bacterial
tribe Rickettsiae, family Rickettsiaceae, and
order Rickettsiales.
Named after HowardTaylor Ricketts, who first recognised the unique nature of
this bacteria causing the Rocky Mountain Spotted fever.

RICKETTSIAS
 Earlier, this group was positioned between viruses and
eubacteria.
 Because of the presence of true cell walls similar to other
Gram negative bacteria, it is now grouped under eubacteria.
 Cell walls are with peptidoglycan.
 Susceptible to Tetracycline antibiotics.
 Causes several human diseases transmitted by arthropod
vectors such as fleas, mites, lice, ticks etc.
 Some of them are fatal too.
 For eg: Typhus fever caused by Rickettsia prowazekii,
transmited by lice to man.

Rickettsia prowazekii

 Important rickettsial diseases.
➢ Rocky Mountain Spotted fever-Rickettsia rickettsi(by ticks)
➢ Endemic typhus or Murine Typhus-R.mooseri
➢ Rickettsial pox orVesicular rickettsiosis-R.akari(by blood sucking
mites)
➢ Scrub typhus-R.tsutsugamushi
➢ Q-fever(influenza like disease infecting respiratory tract)-Coxiella
burnetti
➢ Trench fever among soldiers during World war1-Rochalimaea
quintana

SPIROCHETES

Spirochetes
 are long, slender and helically coiled motile bacteria
 only a fraction of a micron in diameter but 5 to 250 microns
long.
 look like miniature springs or telephone cords.
 Presence of axial filaments
 they enable the bacterium to move by rotating in place.
 run along the outside of the protoplasm, but inside an outer
sheath
Treponema - the only genus to lack the outer sheath.

 Gram-negative.
 Chemotrophic in nutrition.
 there are only six genera and includes
 aerobic and anaerobic species
 free-living and parasitic forms
 syphilis and Lyme disease are caused by these bacteria
 other species are important symbionts in the stomachs of cows
and other ruminants.
 Some species of Treponema live in the rumen of a cow's stomach, where
they break down cellulose and other difficult to digest plant
polysaccharides for their host.

 Spirochetal diseases are characterized by-
 entry through skin or mucus membranes.
 Dissemination via blood, tissue and body fluids, especially to
cardiovascular, neurologic and skin tissues.
 They lack surface proteins on their outer membrane.
 This helps them in immune evasion.
 Neurotropic spirochetes enter the central nervous system
(CNS) early in the course of disease.

 Some of the pathogenic species are significant health
threat to humans.
 Major diseases caused by spirochetes include:
➢ Leptospirosis-Leptospira.
Transmission from animals to humans.

➢ Lyme disease-Borrelia burgdorferi,B.garinii,B.afzelii etc.
➢ Relapsing fever-Borrelia recurrents
➢ Syphilis-Treponema pallidum
➢ Intestinal spirochetosis-Brachyspira pilosicoli

CHLAMYDIAS

CHLAMYDIAS
 Include a group of pathogenic bacteria that are obligate
intracellular parasites.
 Cell is more or les spherical with a diameter of 0.25-
0.30m.
 First recognised in 1930 as the causative agent of a type
of Pneumonia called Psittacosis.
 Gram negative.
 Cannot synthesis its own ATP, and cannot be grown at
artificial medium.

 Exists in 2 stages:
 Infectious particles called Elementary bodies and
 intra cytoplasmic reproductive forms called Reticulate
bodies.
 They alternate with each other.
 Once inside the cell, the elementary body reacts with
glycogen and germinates to reticulate form.
 Capable of binary fission.
 Chlamydia infections-sexually transmitted diseases in
humans, blindness etc.
 Diseases do not cause symptoms.

 Major diseases include:
➢Chlamydia infection-Chlamydia trachomatis
• most common sexually transmitted disease both in men
and women.
• “silent epidemic”
➢Trachoma or Chlamydia conjucivitis-Chlamydia
trachomatis.
• Serious eye infection.
• Inflammation of eye, irritation and thick discharge.
➢Pneumonia- Chlamydia pneumoniae
• Infection in respiratoy tract.
➢Psittacosis(Parrot fever)-C. psittaci
• Carried by parrots.

MYCOPLASMA

Mycoplasma
 do not have a cell wall
 like a tiny jellyfish with a pliable membrane
can take on many different shapes
 make them difficult to identify, even under a
high powered electron microscope.
 very hard to culture in the laboratory
 They can be parasitic or
saprotrophic
 Several species are pathogenic in humans,
including M. pneumoniae
 But they are unaffected by many common
antibiotics

MYCOPLASMA
 Smallest self replicating prokaryotes capable of
generating their own energy.
 Smallest bacterial cells which can survive without
oxygen.
 Lack cell wall.
❖Pleomorphic.
❖Unaffected by antibiotics.
❖Plasiticity of cell allows to pass through bacterial filters.
 Smallest cell have 0.3m diameter.
 Also called as PPLO.

 Sterol containing cell membarane.
 Fried egg or mulberry colonies on agar.
 Mycoplasma pneumoniae causes Atypical
Pneumonia(“walking pnemonia”), sore throat and
inflammation of bronchi in humans.

 M.hominis , M.urealyticum,M.genatalium - “Genital
mycoplasmas”
• Found in the genital and urinal tracts of adults.
• Causes Urethritis and Vaginitis in women.
 Mycoplasmosis in Cats-M.felis, M.gateae, M. feliminutum.

ACTINOMYCETES

ACTINOMYCETES
 Include a group of Gram-positive, filamentous,rod and
coocus, showing branching growth patterns, aerobic
bacteria found abundantly in soil.
 They were called as “Ray fungi” because they formed
branching filaments(hyphae) and mats(mycelium).
 Unlike true fungi, actinomycetes have thin hyphae(0.5-
1.5m in diameter).
 Many genera forms spores, sporangia and spore cases.
 Cell walls with cross-linked polymers containing short
amino acids and long chains of amino sugars.

 Some are harmless to animals and plants,while some are
important pathogens and many others are sources of
antibiotics.
▪ Streptomycin-by Streptomyces griseus.
▪ Tetracycline-by S.aureofaciens.
▪ Neomycin-by S.fradiae
 Majority feed on protein or non protein organic matter.
 Play an important role in soil ecology.
• Produces enzymes that can degrade organic plant material,
lignin, chitin etc.
• Important in the formation of compost.

 Pathogenic forms causes diseases in humans.
 Nocardia spp. causes infection in lungs similar to
tuberculosis.

 Mycobacterium tuberculosis causesTuberculosis.
 Corynebacterium diphtheriae causes diphtheria.
 Corynebacterium pyogenes causes Mastitis,Pharyngitis and
Urethritis in Sheep,cows,swines,horses etc.

 Actinomycosis caused by Actinomyces israelii
❖Characterised by abscesses in mouth, lungs or
gastrointestinal cavities.
❖Sensitive to Penicillin.

MYXOBACTERIA

MYXOBACTERIA
 Myxobacteria are unicellular bacteria
 characterized by complicated multicellular behaviors, such as
 feeding, social movement, aggregation, and fruiting body formation
 It make them highly unusual.
 They are gliding bacteria
 Gliding movement,
 No flagella or cilia.
 Travel in swarms.
 produce fruiting bodies in starvation conditions.
 They are common in animal dung and organic-rich soils
 Some of them grow by utilising cellulose,
 but many of them feed by secreting antibiotics to kill other bacteria
and then produce enzymes to lyse the cells of their prey.

 The vegetative cells of all myxobacteria are aerobic,
Gram-negative, elongated rods with either rounded or
tapered ends

 They glide in water films
across solid surfaces,
secreting slime
(polysaccharide) tracks in
which many cells migrate to
produce feathery
extensions at the colony
margin

 At the onset of nutrient depletion
the cells migrate back along the
slime tracks, aggregating by
chemotaxis, to form large
concentrations of cells.
 These aggregates then develop
into fruiting bodies which are
raised above the agar surface and
typically develop a bright yellow,
red or brown pigmentation.
 As the vegetative cells migrate
upwards into the fruiting body
they undergo a progressive
differentiation into rounded
myxospores

VBNC -viable but non-culturable
 One particular survival strategy in bacteria is the ability to
enter a state that permits endurance to unfavorable
environmental conditions
 VBNC cells are not culturable on routine laboratory media
 Due to their reduced metabolic activity and increased
peptidoglycan cross-linking, manyVBNC bacteria have higher
physical and chemical resistances compared to culturable cells
 VBNC cells remains challenging to microbiologists.
 Until now, approximately 85 species have been shown to enter the
VBNC state, including 67 pathogenic bacteria
 VBNC state is similar to dormancy with the cells retaining
an intact membrane, undamaged genetic material and
metabolic activity.

Nanobes
 miniature organisms of 20 to 150 nanometres
(billionths of a metre) in length
 Discovered by University of Queensland researchers
 are much smaller than the smallest certified terrestrial
bacteria ever found on the planet.
 Researchers discovered the living colonies of organisms
in ancient sandstones retrieved from an oil drilling site 3-
5km below the Australian seabed.

 Nanobes are thought to exist everywhere!
 Nanobe structures have been found within organisms as
well as rocks.
 Nanobes may also exist on other planets!
 some speculate that nanobes may even outnumber
bacteria by an order of magnitude!