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Determination characteristics!! |
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A
total of 11 characteristics are
determined in order to identify filamentous micro-organisms. Some of
these
characteristics are illustrated in Figs A and B
Only a few filamentous bacteria
(Beggiatoa and
Flexibacter) are able to move freely. This occurs by means
of
‘gliding movement’ resembling the manner in which a
worm propels itself. If it is thought that a certain filament appears to move, then it should be verified that there is no liquid flow on the slide owing to evaporation of the water along the edges. The absence or presence of
branching
is an important characteristic for identifying filamentous bacteria in
activated sludge. Real and false branches are distinguished. Actinomycetes and fungi show real branching. The side shoot actually
sprouts from the main branch. With real branching, the cell in fact
grows in
two directions. Sheath forming bacteria,
principally Sphaerotilus natans and
Type 1701,
form false branches. These arise
because ‘swarming cells’ attach themselves to the
sheath around the filament
and subsequently, through cell division, develop into side shoots
(including a
sheath). Swarming cells are cells which
have
split away from the free end of the filament and temporarily, i.e. as
long as
they have not yet become attached, are present in the sludge as free
living
cells. A side branch can also be formed at a spot where damage to the
sheath
has occurred. In the case of false branching,
a
very small space is often visible between the cells in the main branch
and
those in the side shoot. This space is lacking in the case of real
branching.
False branches are always ‘V’ shaped, while real
branches often stand ‘dead
straight’ on the main branch (but not in the case of the
actinomycete Skermania piniformis).
Actinomycetes
always form numerous real branches. A number of branched filaments
gathered
together clearly resemble a bunch of sticks. Fungi are easily
distinguishable
from the sheath forming bacteria and the actinomycetes on account of
their much
more robust filaments. Attachment of single celled
bacteria
to a filament (= attached growth) is sometimes mistaken for branching. Occasionally in the sludge filaments are observed which are attached to each other at their bases. This is known as a rosette of filaments. These bacteria secrete substances with which they attach themselves. Thiothrix and Leucothrix strains mainly form rosettes. Three groups of filament shapes
are
distinguished: · ‘straight’ · bowed/bent · twisted/coiled The word straight has been
placed
between inverted commas, as only
Haliscomenobacter hydrossis forms really dead straight
filaments. Straight
examples are indeed somewhat bent, especially where relatively long
filaments
are concerned. During microscopic investigation, a distinction should be made between (1) straight to slightly bent and (2) bent to coiled filaments. When identifying filaments, a distinction must be made between (1) little or no attached growth and (2) much attached growth. Filamentous micro-organisms are
divided into
three groups on the basis of their diameters: ·
diameter
< 1 mm ·
diameter
1-2.5 mm ·
diameter
> 2.5 µm For some filaments (Type 021N and Thiothrix strains), the cell diameter sometimes gradually decreases towards the tip of the filament. Transverse walls or septa are the walls between consecutive cells of a filament. Septa are not always clearly visible with a light microscope. When identifying filamentous organisms, a distinction should be made between (1) clearly visible and (2) poorly visible/invisible. Where filaments possess much attached growth, attention should be paid to their clean extremities for assessing this feature. The following cell shapes can be distinguished
in free living bacterial cells: · spherical or coccus · rod shaped · spiral shaped · ‘vibrio’
shaped Filamentous micro-organisms
comprise
coccus or rod shaped cells or other cell shapes derived from these
shapes. This
means that the cells in a filament are square or rectangular, if there
are no
constrictions of the communal outside wall at the position of the
transverse
wall. The cells of certain
filamentous
species are surrounded by a transparent cover known as a sheath, which
is not
often visible with a light microscope. The sheaths of some species are
indeed
visible following Gram staining. The sheath is sometimes more easily
visible if
the sludge sample is stored for a few days in a refrigerator. A lot of
attached
growth often indicates that a sheath is present. In addition, it should be noted that empty cells in a filament are sometimes mistaken for sheaths. The transparent empty cells are generally very short. This means that long, transparent covers must be visible in or on the extremities of the filaments before it can be definitely concluded that a sheath is present. As this characteristic is often not properly established, it is of subsidiary importance for the identification of filamentous bacteria in activated sludge. Granules are globules of storage material in
the cells. Three types of granules are distinguished with microscopic
investigation: · polyphosphate
granules. Without Neisser staining these granules are poorly or not
visible at
all; · sulphur
granules. These globules are of a dark shade when still small. On the
other
hand, larger examples are strongly refractive and are consequently
clearly
visible; · other
storage materials. This usually involves poly-b-hydroxybutyrate
(PHB). PHB granules are hardly ever observed in filamentous
microorganisms in
domestic treatment plants. Like the sulphur granules, the PHB granules
are also
strongly refractive. The results
of Gram and
Neisser stainings For information on carrying out these staining methods, follow this link |