Encyclopedia of Environmental Science and Engineering, Volume I and II

MICROBIOLOGY 693

When bonds of ATP indicated by ~ are broken, a con-

siderable amount of energy is released. This ~ bond cleav-

age energy operates the biological engines: it is the universal

chemical power which operates in all cells, autotroph or het-

erotroph.

Chemolithotrophic nutrition is only used by certain true

bacteria. These bacteria are of ecological importance in that

they are used to convert one form of nitrogen to another (i.e.

in the nitrogen cycle) or industrially to oxidize low grade

metallic or non-metallic ores. There are six bacterial groups

which are chemolithotrophic.

1) The ammonia oxidizers such as Nitrosomonas,

Nitrosococcus, Nitrosocystis, Nitrosogloea and

Nitrosospira.

One scheme for ammonia oxidation had hydrox-

ylamine as an obligate intermediate and has been

proposed for Nitrosomonas.

2) The nitrite oxidizers such as Nitrobacter and

Nitrocystis. One proposed scheme for nitrite oxi-

dation for Nitrobacter is:

NO

cytochrome

reductase

cytochrome C

cytochrome

oxi

2

 ⎯→⎯⎯⎯ ⎯ →⎯⎯⎯

ddase

O

ATP ADP

2

3) Hydrogen oxidizers Hydrogenomonas. One pro-

posed hydrogen oxidation scheme is:

H 2 →2H^ 
^ 
 2e→unknown→fl avor protein compound

→ubiquinone→O 2

cytochrome

b compex

Nicotinamide adenine→menadione

→cytochrome C→cytochrome a

→O 2 dinucleotide (NAD)

4) Ferrous compound oxidizing bacteria such as

Ferrobacillus and Thiobacillus ferroxidans.

One proposed ferrous oxidizing scheme for

F. ferrooxidans is:

4FeCO 3 
 O 2 
 6H 2 O→4Fe(OH) 3 
 4CO 2

5) Methane oxidizers such as Methanomonas methano-

oxidans and Pseudomonas methanica are common

in the upper layers of marine sediments and soil.

Methane is oxidized in the following manner:

CH 4 →CH 3 OH→HCHO→HCOOH→CO 2

6) The sulfur-compound oxidizing bacteria Thioba-

cillus.

Four pathways for oxidation of thiosulfate (S 2 O 3 
^2 ) by

different Thiobacillus species are known. These are:

a) 6Na 2 S 2 O 3 
 SO 2 →4Na 2 SO 4 
 2Na 2 S 4 O 6

2Na 2 S 4 O 6 
 6H 2 O 
 7O 2 →2Na 2 SO 4 
 6H 2 SO 4

b) Na 2 S 2 O 3 
 2O 2 
 H 2 O→Na 2 SO 4 
 H 2 SO 4

c) 5Na 2 S 2 O 3 
 H 2 O 
 4O 2

→5Na 2 SO 2 
 H 2 SO 4 
 4S

2S 
 3O 2 
 2H 2 O→2H 2 SO 4

d) 2Na 2 S 2 O 3 
 H 2 O 
 1/2O 2 →Na 2 S 4 O 6 
 2NaOH

Photolithotrophic nutrition is used by photosynthetic

bacteria, blue green algae and eukaryotic algae. The general

reaction in which both utilization of CO 2 (carbon dioxide

fi xation) and energy generation is summarized is:

CO 22 

H A⎯→nv⎯()2CH O 2 A
H O 2

Where A is either oxygen for all eukaryotic algae and the

prokaryotic blue-green algae (H 2 A = H 2 O), or sulfur for green

sulfur bacteria, Chlorobacteriaceae, and purple sulfur bacte-

ria, Thiorhodaceae (H 2 A = H 2 S) or any one of several organic

compounds for nonsulfur purple bacteria, Athiorhodaceao

(H 2 A = H 2 -organic compound which is oxidizable).

Both green and purple sulfur bacteria are obligate

anaerobes whereas the non-sulfur purple bacteria are facul-

tative anaerobes (they are anaerobic when growing hetero-

trophically). In all cases, photosynthetic organisms operate

by the initial transduction of light to chemical energy. In

this transduction, chlorophyll 
 light quanta Ch1^ 
^ (excited

chlorophyll) 
 e (electron driven off of Ch1). Many such

events take place simultaneously and electrons released

during these reactions migrate through the photosynthetic

unit to the reaction center and transfer energy to a special

reaction-center chlorophyll. At the reaction center, a charge

separation of the oxidant and reductant occurs. Electron

fl ow after this event differs in photosynthetic bacteria as

compared with algae and higher plants (Figures 9 and

10). In addition, differences in photosynthetic ability exist

among organisms based upon the absorption maxima of

their light-transducing pigments (primarily chlorophylls).

The combination of light intensity, wavelength of available

light, wavelength of operation of principal energy trans-

ducing pigment, degree of aerobiasis, and availability of

oxidizable compound (H 2 O, H 2 S, or H 2 -organic compound)

all infl uence the effi ciency of photosynthesis. These factors

should be borne in mind when one looks for the ecological

niche occupied by these various organisms.

Ecology of Microorganisms

One should understand the physiological requirements of

microorganisms before investigating the effects of environ-

mental changes on the distribution and activity of diverse

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