Environmental Microbiology of Aquatic and Waste Systems

4.1 Taxonomy of Microorganisms in Aquatic Environments 59

tosynthesis, but there are differences between the

two; for instance, unlike plants, they do not pro­

duce oxygen during photosynthesis. The process

of photosynthesis in the bacteria and in higher

plants is discussed more fully below.

5. Deinecoccus­Thermus
   The Deinococcus­Thermus are a small group of
   Gram negative bacteria comprised of cocci which
   are highly resistant to environmental hazards
   because they are able to quickly repair damage
   to their DNA. There are two main groups. The
   Deinococcales include a single genus, Deino­
   coccus, with several species that are resistant to
   radiation; they have become famous for their
   ability to “eat” nuclear waste and other toxic
   materials, survive in the vacuum of atmosphere
   space, and survive extremes of heat and cold.
   Thermus spp. include several genera resistant to
   heat. Deino coccus radiodurans is an extremophilic
   bac terium, and is the most radioresistant organ­
   ism known. It can survive heat, cold, dehydration,

vacuum, and acid, and because of its resistance to

more than one extreme condition, D. radiodurans

is known as a polyextremophile.

Thermus aquaticus is important in the develop­

ment of the polymerase chain reaction (PCR) where

repeated cycles of heating DNA to near boiling

make it advantageous to use a thermostable DNA

polymerase enzyme. These bacteria have thick cell

walls that give them Gram­positive stains, but they

include a second membrane and so are closer in

structure to those of Gram­negative bacteria.

6. Spirochetes
   Spirochetes are Gram­negative bacteria, which
   have long, helically coiled cells. Spirochetes are
   chemoheterotrophic in nature, with lengths
   between 5 and 250 mm and diameters around
   0.1–0.6 mm. Spirochetes are distinguished from
   other bacterial phyla by the presence of flagella,
   sometimes called axial filaments, running length­
   wise between the cell membrane and an outer
   membrane. These cause a twisting motion which

Aquifex

Thermodesulfo

bacterium

Thermotoga

Green non-sulfur

bacteria

Green sulfur

bacteria

Flavobacteria

Deferribacter

Cytophaga

Verucomicrobia

Chlamydia

Cyanobacteria

Actinobacteria

Gram-positive bacteria

Nitrospira

ε-Proteobacteria

δ-Proteobacteria

α-Proteobacteria

β-Proteobacteria

γ-Proteobacteria

Planctomyces/

Pirella

Deinococci

Spirochetes

Fig. 4.10 Bacterial groups according to the 16S RNA classification