Environmental Microbiology of Aquatic and Waste Systems

72 4 Taxonomy, Physiology, and Ecology of Aquatic Microorganisms

The anammox bacteria are characterized by several
striking properties:
(a) They all possess one anammoxosome, a membrane
bound compartment inside the cytoplasm which is
the site of anammox catabolism.
(b) Further, the membranes of these bacteria mainly
consist of ladderane lipids which are rare in living
organisms.
(c) Hydrazine (normally used as a high­energy rocket
fuel, and poisonous to most living organisms) is a
by­product of these organisms.
(d) Finally, the organisms grow very slowly, the gen­
eration or doubling time being nearly 2 weeks.
The anammox process was originally found to
occur only from 20°C to 43°C, but more recently, ana­
mmox has been observed at temperatures from 36°C to
52°C in hot springs and 60°C to 85°C at hydrothermal
vents located in the ocean floor.
Reduction under anaerobic conditions can also occur
through anaerobic ammonia oxidation (Anammox) thus:

Because denitrifying bacteria are principally het­
erotrophic, in some wastewater treatment plants, small
amounts of methanol are added to the wastewater to
provide a carbon source for the bacteria.
Nitrogen fixation, nitrification, and denitrification
are interlinked in the nitrogen cycle. The nitrogen
cycle in the marine environment is given in Fig. 4.1 5.

The Sulfur Cycle in the Aquatic System and

Bacteria

In the environment, through changes brought about

mostly by bacteria, sulfur changes from one form to

the other: From hydrogen sulfide (H 2 S) to sulfate via

elemental sulfur (S^0 ) and sulfate is changed again to

hydrogen sulfide. Hydrogen sulfide is also evolved

from hot springs and volcanoes, and occurs when dead

animals, the excreta of animals, and dead plants are

decomposed by bacteria. The compound is oxidized to

sulfuric acid by the sulfur­oxidizing bacteria and pho­

tosynthetic sulfur bacteria via elemental sulfur. The

change of hydrogen sulfide to elemental sulfur occurs

also abiotically in the presence of molecular oxygen.

Dimethyl sulfide (CH 3 ) 2 S is produced by marine

algae and marine cyanobacteria and contributes to the

typical smell of thee sea. Dimethyl sulfide is degraded

by bacteria such as Thiobacillus and Hyphomicrobium,

leading to the formation of acid. The various transfor­

mations are summarized in Fig. 4.1 6. A major group of

bacteria important in the global economy of sulfur,

especially in aquatic environments are the sulfate reduc­

ing bacteria. They will be discussed briefly below.

The sulfate reducing bacteria (SRB) are ubiquitous

anaerobes found in diverse environments. They include

several groups of bacteria that use sulfate as an oxidiz­

ing agent, reducing it to sulfide (Fig 4.1 7 ) (Luptakova

2007 ). They can also utilize other sulfur compounds,

including sulfite, thiosulfate, and elemental sulfur in

a type of metabolism known as dissimilatory, because

NH 4 NO2 22N 2H O.

+−+ →+

Oxidation

state

Anammox

Assimilation

Nitr

ification

Assimilation

(NH 3 )NORG N H 3

N 2 O

N 2

(X) (Y)

+V

+IV

+III

−III

+II

−II

+I

−I

0

N 2 O

NO 2 − NO 2 − NO 2 −

NO 3 −

Catabolism

Denitr

ification

Nitrogen Fixation

Fig. 4.15 Nitrogen cycle
in the marine environment
(From Codispoti et al. 2001.
With permission)
“X” and “Y” are intracel­
lular intermediates that do
not accumulate in water
column