Environmental Microbiology of Aquatic and Waste Systems

4.1 Taxonomy of Microorganisms in Aquatic Environments 77

survive without cellwalls but they also survive

high temperatures and low acid conditions. For

these conditions, these organisms have special

polysaccaride structures in their cell membranes, a

lipopolyssacharide.

4. Hyperthermophilic Archae: Well-known members of
   this group are Thermococcus, Pyrococcus, and
   Methanopyrus. Members of this group have optimal
   temperatures of 80°C and many grow at tempera­
   tures higher than that of boiling water. Thus
   Thermococcus and Pyrococcus (cocci with a tuft of
   flagella on one side) grow at between 70°c and 106°C
   with an optimum at 100°C (Pyrococcus). Proteins,
   starch or maltose are oxidized as electron donors and
   S^0 is the terminal acceptor and is reduced to H 2 S.

Crenarchaeota

Crenarchaeota has the distinction of including microbial

species with the highest known growth temperatures of

any organisms. As a rule, they grow best between 80°C

and 100°C and several species will not grow below

80°C. Several species also prefer to live under very

acidic conditions in dilute solutions of hot sulfuric

acid. Approximately 15 genera are known, and most of

the hyperthermophilic species have been isolated from

marine or terrestrial volcanic environments, such as

hot springs and shallow or deep­sea hydrothermal

vents. Recent analyses of genetic sequences obtained

directly from environmental samples, however, indicate

the existence of low temperature Crenarchaeota, which

have not yet been cultivated. The most spectacular fea­

ture of the Crenarchaeota, however, is their tolerance

Solid Organic

Matter

Complex

dissolved

organic matte

Hydrolysis

Dissolved Organic

Matter

Fermentative

bacteria

Acetogenic

bacteria

Fattyacids & Acetate

alcohols

Hydrogen

H 2

Carbon

dioxide

(CO 2 )

Methane

CH 4

Methanogenic

bacteria

(acetophilic)

Methanogenic

bacteria

(hydrogenophilic)

Methanogenic

bacteria

(methylophilic)

Methylated compounds

Fig. 4.18 Substrates and bacterial groups involved in methane production (After Christen and Kjelsen 1989)