Page 235 - (DK) Ocean - The Definitive Visual Guide

BACTERIA AND ARCHAEA 233

DOMAIN BACTERIA DOMAIN BACTERIA brown. Unusually, the filament grows
in much the same way as a plant root,
Oscillatoria willei Calothrix crustacea its growth being confined to a special
region just behind the tip, called a
SIZE Filament length 0.13mm SIZE Filament length 0.15mm meristem. Sometimes, the filament
DISTRIBUTION Tropical waters DISTRIBUTION Worldwide sheds the tapering tip above the
growth region, enabling Calothrix
Once known as blue-green algae, Forming single filaments or small to reproduce asexually by casting off
cyanobacteria are bacteria that are able bundles, bacteria of the genus Calothrix fragments called hormogonia from the
to use photosynthesis to make foods are widespread in oceans everywhere. meristem. These fragments are able to
in a similar way to plants. Oscillatoria Unlike those of Oscillatoria and form new filaments far away from the
willei and other related cyanobacteria Trichodesmium (left), the filaments parent. These kinds of cyanobacteria
occur in rows of similarly sized cells of Calothrix crustacea have a broad often form slimy coatings on coastal
that form filaments called trichomes. base and a pointed tip that ends in rocks and seaweeds. At least one
Many trichomes are enveloped in a a transparent hair. The filament has species of Calothrix is known to make
firm casing, but in Oscillatoria the a firm or jelly-like coating, which up the photosynthetic part of some
casing is thin or may be absent Fragments of filaments, called is often made up of concentric layers rocky shore lichens, such as Lichina
altogether, which allows the filaments hormogonia, which consist of dozens that may be colourless or yellow- pygmaea (p.255).
to glide quickly forwards, backwards, of cells, sometimes break off and glide
or even to rotate. Some species of away to establish new colonies. These
Oscillatoria can fix nitrogen but, unlike bacteria may cause skin irritations in
Trichodesmium (below), they may not humans who come into contact with
have cells specialized for the purpose. them in tropical waters.

DOMAIN BACTERIA oceanic food chains. The bacteria
form long colonial filaments, in
Trichodesmium which some cells carry out nitrogen
erythraeum fixation, while others are specialized
for photosynthesis. These tasks
must be separated because the
SIZE 1–10mm per colony
oxygen by-product that results from
DISTRIBUTION Tropical and subtropical seas photosynthesis would interfere with
worldwide
the nitrogen-fixing process, so they
cannot both occur in the same cell.
Individual filamentous colonies of the
cyanobacteria Trichodesmium erythaeum
are just visible to the naked eye, and
these bacteria have traditionally been
known as sea sawdust by mariners.
Under warm conditions, the bacteria
is able to multiply extremely rapidly
to create massive blooms that may
have such an extent that they are
visible from space.
This is a prolific nitrogen-fixing
bacterium that harnesses about half
of the nitrogen passing through

DOMAIN BACTERIA the bacteria live within the body DOMAIN ARCHAEA
of their host in a mutually beneficial EYE LIGHTS
Vibrio fischeri relationship. The bacteria produce Halobacterium
light using a chemical reaction that Eyelightfish (such as the one
SIZE 0.003mm cell length takes place inside their cells. Vibrio shown below) have light-emitting salinarium
DISTRIBUTION Worldwide fischeri also occurs as a free-living organs called photophores under SIZE 0.001–0.006mm
organism, moving through water by each eye. The light is produced by
Many marine organisms, particularly means of a flagellum and feeding on colonies of Vibrio fischeri living in DISTRIBUTION Dead Sea and other hypersaline areas
of the world
those in the deep sea, make use of dead organic matter. The distinctive, the photophores. The light organs
bioluminescence, the biochemical comma-shaped cells seen in Vibrio can be covered and uncovered,
emission of light. Many of these fischeri, below, are characteristic of the and may be used as an aid to Archaea that have adapted to live in
creatures depend on bacteria, such genus. Other Vibrio species (which are recognition and communication waters with exceptionally high salt
as the rod-shaped Vibrio fischeri, to not luminescent) are responsible for between fish of this species. The concentrations are called halophiles.
generate the light, and in these cases the potentially fatal disease cholera. ability to emit light may also play One example of this type of organism
a part in prey capture and the is Halobacterium salinarium, which is
avoidance of predators. rod-shaped, produces pink pigments
called carotenoids, and forms extensive
areas of pink scum on salt flats. The
cell membranes of halophiles contain
substances that make them more stable
than other types of cell membrane,
preventing them from falling apart in
the high salt concentrations in which
they live. Their cell walls are also
modified, for the same function.
These archaea obtain nourishment
from organic matter in the water. OCEAN LIFE
In addition, their pigments absorb
some light energy, which the bacteria
then use for fuelling processes
within the cells.