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Culturing and Morphological identification of
Algae
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AIM:
To
culture and to study the morphology of algae from the natural habitats.
GENERAL
FEATURES:
Algae
include species that fall under the Division Cyanophyta, Kingdom Eubacteria.
They are referred to as algae but are actually photosynthetic bacteria that
appear like true algae. They are mostly single-celled organisms or aggregations
of single-celled organisms (planktonic). Planktonic algae generally do not
adhere together in a mass, in that you could not easily grab a handful or mass
of these organisms. Some species, such as Nostoc, are gelatinous masses that
can be picked up. Anabaena, Aphanizomenon, Oscillatoria and Mycrocystis often
dominate plankton communities and are notorious for producing potentially toxic
blooms in fresh waters. These toxins can cause death and illness in livestock;
and gastroenteritis, liver damage and skin and eye irritations in humans. High
numbers of blue-greens often indicate high nutrient levels in the water,
although Oscillatoria can form dense accumulations in less fertile waters. Cell
colour is uniform throughout (i.e. no membrane-bound coloured structures called
chloroplasts) and may appear blue-green to violet, but sometimes red or green.
They have very simple internal structure, no definite nucleus or intracellular
membranebound organelles.
PRINCIPLE:
Algae
(singular alga) encompass several groups of relatively simple living aquatic
organisms that capture light energy through photosynthesis, using it to convert
inorganic substances into organic matter. Algae range from single-cell
organisms to multicellular organisms, some with fairly complex differentiated
form and (if marine) called seaweeds. Algae are usually found in damp places or
water bodies and thus are common in terrestrial as well as aquatic
environments. Various algae play significant roles in aquatic ecology. Algae
are used by humans in a number of ways. Because many species are aquatic and
microscopic, they are cultured in clear tanks or ponds and either harvested or
used to treat effluents pumped through ponds. Algae Culture Agar is recommended
for the isolation and cultivation of algae from soil, water and sewage.
MATERIALS REQUIRED: Sample water, Algae culture
media, Light source, Glass tank or vessel, Glass slide, Inoculation loop,
Microscope, aerator.
Algae Culture Media components:
Algae Culture Agar is recommended for the
isolation and cultivation of algae from soil, water and sewage. Also for
carrying stock cultures of algae used in the bioassay of algicidal chemicals.
Composition**
Ingredients Gms / Litre
Sodium
nitrate 1.000
Dipotassium
phosphate 0.250
Magnesium
sulphate 0.513
Ammonium
chloride 0.050
Calcium
chloride 0.058
Ferric
chloride 0.003
Agar
15.000
Final
pH ( at 25°C) 7.0±0.2
Sample collection:
Sampling
of large bodies of fresh water occurred at multiple sites along the waterfront
nearby our college. Collections were made for the top and bottom of the water
bodies. All field samples were collected in 50 mL tubes and maintained at
refrigerated condition while transferring to laboratory.
Isolation & Cultivation:
1.
The
samples were first diluted to aid in the isolation process.
2.
Sterilized
plastic petri dishes (100 × 15 mm) containing approximately 40 mL of agarized
medium were used to plate these diluted samples.
3.
One
milliliter of the diluted sample was transferred to a media plate and spread
evenly across the surface.
4.
Inoculated
plates were placed in a temperature-controlled greenhouse (20-25°C,
approximately 27 µE/m/s) where the algae were allowed to grow for about 14
days.
5.
Grown
algae cultures were streaked using sterile technique onto additional sets of
nutrient media plates and placed back in the greenhouse for isolation.
6.
This
streaking method was repeated until isolation into axenic unialgal cultures was
achieved. Isolated algae were maintained as stock cultures and were stored on a
cool, low light shelf.
Morphological identification
1.
Microalgal
and cyanobacterial cultures were initially separated based on morphological
examination of the colonies on an agar nutrient medium.
2.
This
general classification method was only used to distinguish isolates on the most
basic level. Identification of these isolates to the genus level was based on
the morphology of the individual cells following microscopic examination.
3.
Place
a loopful of water sample on the grease free slide and put a cover slip over
it. Observe the slide under the microscopic objectives at 10x and 40x.
4.
The
strains were identified using the methods similar to reported by Wehr and
Sheath.
RESULT:
All
of the isolates were categorized based on the morphological appearance of the
culture and the microscopic cellular appearance of the isolated colonies.
