Environmental Microbiology of Aquatic and Waste Systems

60 4 Taxonomy, Physiology, and Ecology of Aquatic Microorganisms

allows the spirochete to move about. The spiro­

chete shape may also be described as consisting of

an axial filament around which the cell is wound

giving spirochetes their characteristic corkscrew

shapes. Most spirochetes are free­living and anaer­

obic, but they also include the following disease­

causing members:

• Leptospira species, which causes leptospirosis
  (also known as Weil’s disease)


• Borrelia burgdorferi, which causes Lyme disease


• Borrelia recurrentis, which causes relapsing
  fever


• Treponema pallidum, which causes syphilis

7. Green sulfur bacteria
   Green Sulfur Bacteria are found in anaerobic
   environments such as muds, anaerobic, and sul­
   fide­containing fresh or marine waters, and wet­
   lands. These anoxygenic phototrophic bacteria
   live in environments where light and reduced
   sulfur compounds are present. They are found
   most often under the Purple Sulfur bacterial
   layer. Green sulfur bacteria are capable of using
   sulfide or elemental S as the electron donor. The
   elemental S arises from H 2 S oxidation and is
   deposited extracellularly, before the oxidation of
   sulfate. There are four genera of green sulfur
   bacteria, Chlorobium, Prosthecohloris (with stalks
   or prostheca), Pelodictyon (with vacuoles), and
   Clathrochloris (motile).
   The Green Sulfur Bacteria strains are green
   because of the presence of bacteriochlorophylls
   (bchls) “c” and “d” and small traces of bchl “a”
   located in chlorobium vesicles attached to the
   cytoplasmic membrane. Some are brown and they
   contain bacteriochlorophyll “e.” These brown
   strains are found in the deeper layers of wetlands
   and water. Both of the two groups can be found
   also living in extreme conditions of salinity and
   high temperatures. The morphology of both color
   types is most often either straight or curved rods.
   They are non­motile phototrophic short to long
   rods which utilize H 2 S as electron donor oxidizing
   it to SO 2 and to SO 4 2+. The sulfur so produced lies
   outside the cells. Light energy absorbed by
   Bacteriochlorophylls c, d, or e is channeled to
   Bacteriochlorophyll a, which actually carries out
   photosynthetic energy conversion, and ATP syn­
   thesis takes place. A well­known member is
   Chlorobium tepidum.

In marine environments, they are found in the

water column where hydrogen sulfide diffuses up

from anaerobic sediments and where oxygen dif­

fuses down from surface waters where oxygenic

photosynthesis is taking place. In the Black Sea, the

largest anoxic water body in the world, they are

found at a depth of 100 m (Manske et al. 2008 ).

They also live in special tissues in invertebrates such

as Riftia pachyptila (vestimentiferan tube worms)

and Calyptogena magnifica (“giant” white clams)

that live around deep sea hydrothermal vents. There

they provide energy, by oxidizing reduced sulfur

compounds, and organic matter, by converting car­

bon dioxide to organic compounds, which the inver­

tebrates use. They are sometimes abundant in coastal

waters, and several members of the group have gas

vacuoles in their cells to help them float.

8. Flavobacteria
   Flavobacteria are Gram negative rods that are
   motile by gliding and found in aquatic environ­
   ments, both freshwater and marine, and in the soil.
   Colonies are usually yellow to orange in color,
   hence their name. Flavobacteria are a group of
   commensal bacteria and opportunistic pathogens.
   Flavobacterium psychrophilum causes the septi­
   cemic diseases of rainbow trout fry syndrome and
   bacterial cold water disease. They decompose sev­
   eral polysaccharides including agar but not cellu­
   lose. The type species is F. aquatile.


9. Defferibacter
   These are thermophilic, anaerobic, chemolithoau­
   totrophic Gram negative straight to bent rods.
   They can use a wide range of electron acceptors
   including Fe3+ and Mn2+. They are found in a wide
   range of aquatic environments including deep­sea
   hydrothermal vents. A well­known member is
   Deferribacter desulfuricans


10. Cytophaga
    Cytophaga are unicellular, Gram­negative gliding
    bacteria. They are rod­shaped, but specific strains
    differ in diameter and length with some being
    pleomorphic (many shaped). The type species is
    C. johnsonae, which has a moderately long thin
    shape. Many strains are red, yellow, or orange
    because of unique pigments synthesized by the
    group. Cytophaga strains tend to be versatile in
    making these and one strain may synthesize 25
    different structural varieties of pigment. The main
    habitats of Cytophaga are soils at or close to neu­