Big Bacteria: The Giant microbes

1. Presented by: Kirandip Kaur

2. Fundamental properties
 Small number of prokaryotic species have unique
physiology by development of unusually large size.
 The biomass of bacteria varies from the 0.2 µm wide to
diameter of 750 µm.
 Large prokaryotes are either cyanobacteria or sulfide
oxidizers.
 Contain numerous inclusions which reduce the volume of
active cytoplasm.
 Ability to store nitrate and sulfur.

3. Organism Characteristics Size (µm) Biovolume (µm)
Thiomargarita
namibiensis
Spherical sulfur bact. 750 200,000,000
Thioploca araucae Filamentous sulfur bact. 43×30 40,000
Beggiatoa spp. Filamentous bact. 160×50 1,000,000
Achromatium oxaliferum Ellipsoid sulfur bact. 35×95 80,000
Thiovulum majus Spherical sulfur bact. . 18 3,000
Epulopiscium fishelsoni Heterotrophic gut bact. 600×80 3,000,000
Lyngbya majuscula. Filamentous cyanobact. 80×8 40,000
Prochloron sp. Phototrophic bact. 30 14,000
Magnetobacterium
bavaricum
Magnetotactic bact. 2×10 30
Staphylothermus
marinus
Archaea 15 1800

4. Thiomargarita Namibiensis
 Gram-negative
 colorless, spherical chain forming
 non-motile
 chemolithotrophic Proteobacterium.
 100–300 μm wide but some cells up to 750 μm
can occur.
 Held together in a string by a mucous sheath.
 Due to their light refracting sulfur globules
 Thus appear as a string of pearls.
 This appearance inspired the name “sulfur
pearl of Namibia”
A string of Thiomargarita
namibiensis . Single cells are about
150 μm in diameter.

5. Spherical cells
Barrel- shaped cells
Large cells : an adaptation
Cells are not visible to naked eye
only 2% of the biovolume
consists of active cytoplasm.
Numerous inclusions resemble
polyphosphate
A) Spherical cells B) Barrel-shaped cells.
A single cell of Thiomargarita
namibiensis in the light
microscope: Apart from the large
sulfur globules numerous smaller
inclusions are visible. The cell
appears hollow.
A
B

6. Physiology
 Oxidizes hydrogen sulfide to elemental sulfur while reducing nitrate to ammonia.
 Preferentially use oxygen in place of nitrate (facultative anaerobe)
 Uptake nitrate for storage so that they can Survive long periods.
 These reactions release enough energy to make ATP.
 Therefore, T. namibiensis must scavenge as much nitrogen as possible and store it
within a large central vacuole for the lean times.
 Gain energy by the breakdown of internally stored polyphosphate.
H2S
NO3-
O2

7. Reproduction
A) A cell dividing in one plane.
B) Synchronized division within a string leading to pairs of cells.
C) A cell dividing in two planes.
 Majority of cells divide in one plane.
 Large cells divide in more than one plane.
 The mucus between newly divided cells is very thin but keeps accumulating over
time, leading to a breakage of longer chains.
A C
B

8. Enrichment
 Not yet cultivated pure culture.
 Thiomargarita can survive as long as the activity of sulfate
reducing bacteria remains moderate and sulfide
concentrations does not become toxically high.
Importance:
 Play an important role in the long-term removal of
phosphorus from the biosphere.
A Namibian stamp
from February 2003
celebrating recent
biological discoveries in
Namibia.

9. Beggiatoa
 Gram negative, filamentous rectangular proteobacteria.
 Grow heterotrophically in the presence of oxygen.
 Form white filamentous mats on top of sulfide-rich
sediments.
 Variable filament length and widths from <1μm to 200μm.
 Straight or bent filaments move free in the water by
gliding movement.
 Filaments can withstand even strong currents.
 in situ sulphur storage

10. Physiology
 Needs molecular oxygen, but adapted to micro-aerophilic conditions
 Reduced sulphur compounds (H2S, Thiosulphate) are required as an energy source
and electron donor.
 Many strains use short chain fatty acids as their carbon source.
 Accumulates nitrate up to 100–200 mM concentration.
 Filaments also have phobic response to light.
 The intermittent exposure to light may be harmful.
 Prefer areas rich in hydrogen sulfate, including water that has been contaminated
with sewage.
 Mats are good indicators of pollution in water.

11. Thioploca araucae
Seen with the naked eye.
Live as bundles of 15–40 µm thick filaments in a common sheath.
Form filament that stretch up from the sediment surface, which resemble a lawn of
white grass.
 Obligate anaerobes or microaerophiles.
 Central vacuole store nitrate at up to 500mM concentration.
 Do not use oxygen as an electron acceptor, but only
Nitrate that is reduce to ammonium.

12. Contd.
If water oxygen concentrations are above 10% air saturation retreat
into their sheaths.
Prolonged periods of oxygenated water reduce the population.
Absorbs nitrate from the water and retires to a dwelling site under the
seabed.
Previously believed that nitrogen removal occured due to Thioploca.
Anammox bacteria that steal nitrate from Thioploca when it retires
through the sheath with its harvest of nitrate.
Thioploca filament secrets slime while
gliding.

13. The sheath material of Thioploca accumulates as the trichomes are gliding up and
down in the sediment. Thus, the trichomes preserve successful routes through the
sediment, which serve as highways and guide the filaments in their chemotactic
movement.
The total areal nitrate uptake of the sediment increases tenfold when the Thioploca
extend out of their sheaths compared to when they are retracted.

14. Achromatium oxaliferum
(Largest free living single-celled prokaryotes)
 Gram negative sulfur bacteria.
 Found in freshwater and brackish environments.
 Posess highly variable sizes with biovolumes of <1,000 to 80,000 µm3.
 Motile by peritrichous flagella.
 Precipitates intracellular calcium carbonate.
 Greater than 70% of this may be occupied by
intracellular inclusions of calcite.
 Presence of sulfur inclusions within the bacterium.
 Oxidize sulfide to sulfate via internally stored sulfur globules and appear
to play a role for sulfide oxidation.

15. Thiovulum majus
 Fastest and largest swimmers.
 Increase their food supply by motility.
 Gram-negative, round to ovoid, 5-25 μm in diamete.r
 Motile by peritrichous flagella.
 Cytoplasm is often concentrated at one end of the cell.
 Remaining space being occupied by a large vacuole and also have sulfur inclusions.
 Perform directional swimming relative to a chemical gradient.
 Thrives at the interfaces of hydrogen sulfide and oxygen in nature.
 Similar to protozoa, rotate and swim in a helical path with 3–10 rotations per sec.
 Microaerophilic.

16. Lyngbya majuscule
Free-living, benthic, filamentous cyanobacteria.
Form periodic nuisance blooms in lagoons, reefs and estuaries.
Produces toxins causing-dermatitis, promote skin cancer and asthma.
Cells are 30 to 40 μm wide and 5 μm thick.
Cells have a thick, gelatinous sheath and a distinct
dark colouration.
Non-heterocystous.
High nitrogen fixation rates have been recorded.
Produce secondary metabolites as lyngbyatoxin A (LTA).

17. Epulopiscium fishelsoni
 Anaerobic, Gram-positive, rod shaped and spore forming clostridia with low
G+C.
 commonly 10–20μm wide and 70–200μm long.
 wrinkled outer membrane with many pockets and folds.
 Symbiotic bacteria found in the guts of herbivorous surgeonfish from the Red
Sea and the Great Barrier Reef of Australia in 1985.
 Cells contain large amounts of DNA that forms a mesh of numerous nucleoids
along the periphery.
 The unsual cortex consist of Vesicles, capsules, and tubules structures.
 Vesicles have excretory function.

18.  E. fishelsoni have a natural circadian rhythm that corresponds with the
feeding and daily activities of the surgeonfish.
 During day light hours E. fishelsoni is active, mobile, and inhibits the pH
within the surgeonfish’s gut.
 Surgeonfish feed on primarily algae or other plant materials which further
inhibits the pH within its gut.
 During the dark portion of the circadian rhythm E. fishelsoni finish
reproduction and become inactive, immobile, which does not inhibit the pH
of the gut, causing it to rise.
 E. fishelsoni usually reproduce by forming daughter cells within the original
(mother) cell.
 They can form up to 7 daughter cells.
 This growth is thought to be associated with the circadian rhythm and thus
makes it very hard to grow these organisms in vitro.

19.  Metabacterium polyspora, an intestinal symbiont of rodents and also
grows to unusual size, forms two or more refractile endospores per cell
and may point toward the evolution of the Epulopiscium.