Environmental Microbiology of Aquatic and Waste Systems

4.1 Taxonomy of Microorganisms in Aquatic Environments 65

Delta (d) Proteobacteria)

The Deltaproteobacteria comprise a group of pre­

dominantly aerobic genera, the fruiting­ body­

forming myxobacteria, and a branch of strictly

anaerobic genera, which contains most of the

known sulfate­reducing bactria, (Desulfovibrio,

Desulfobacter, Desulfococcus, Desulfonema, etc.)

and sulfur­reducing bacteria (e.g., Desulfuromonas)

alongside several other anaerobic bacteria with

different physiology (e.g., ferric iron­reducing

Geobacter and Pelobacter and Syntrophus species,

which live symbiotically together).

Epsilon (e) Proteobacteria

The Epsilonproteobacteria consist of only a few

genera, mainly the curved to spiral­shaped

Wolinella, Helicobacter, and Campylobacter.

Most of the known species inhabit the digestive

tract of animals and humans and serve as symbi­

onts (Wolinella in cows) or pathogens (Helicobacter

in the stomach and Campylobacter in the duode­

num in humans). There have also been numerous

environmental sequences of epsilons recovered

from hydrothermal vent and cold seep habitats.

4.1.4.2 Aspects of the Physiology and Ecology
of Microorganisms in the Aquatic
Environment
This section will discuss the physiology of some of
the activities of aquatic microorganisms which con­
tribute to their ecology in bodies of water as well as
to their economic importance. Items to be discussed

are photosynthesis, nitrogen economy, especially

nitrogen fixation, sulfate reduction, and iron in the

aquatic environment.

Photosynthesis

Photosynthesis is the conversion of CO 2 to carbohy­

drates using light energy. This process has been described

as the most important biological reaction on earth, since

it is the means by which the energy of the sun is

harnessed by living things, through their consumption

of the products of photosynthesis. Photo synthesis is

carried out by plants, algae, and some bacteria, but not

by Archae. It is an important factor affecting the ecol­

ogy of microorganisms in aquatic environments

(Achenbach et al. 2001 ). Photosynthesis is generally

better known in plants than in bacteria; plant photosyn­

thesis will therefore be discussed as a basis for under­

standing bacterial photosynthesis (see Fig. 4.1 1 ).

Photosynthesis is hinged on three items: (a)

Photosynthetic pigments, (b) the light or light­depen­

dent reactions of photosynthesis, and (c) the dark or

light­independent reactions of photosynthesis.

The Pigments of Photosynthesis

A pigment is any substance that absorbs light. The

color of the pigment comes from the wavelengths of

light reflected by the pigment (in other words, those

not absorbed). Chlorophyll, the green pigment com­

mon to all photosynthetic cells, absorbs all wave­

lengths of visible light except green, which it reflects,

and thus is detected by human eyes as green. Black

pigments absorb all of the wavelengths that strike

Photosynthetic

electron

transport

Calvin cycle

ATP

NADPH

ADP + PI

NADP+

H 2 O O 2

CO 2 Sugars

Chlorophyll

Bacteriochlorophyll

Light
Fig. 4.11 Overview
of photosynthesis
(Modified from Moroney
and Ynalvez 2009 )