Culturing and Morphological identification of Algae

 

 

Culturing and Morphological identification of Algae

 

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.