Marine Biotechnology Lab Algal Culture Methods

Types of algal culture methods There are two basic methods for culturing algae. Batch culture. Continuous culture.

Batch Culture In this method algal cells are allowed to grow and reproduce in a closed container (i.e. closed system) in which there is no input or output of materials. The algal population cell density increases constantly until the exhaustion of some limiting factor, while other nutrient components of the culture medium decrease over time. When that nutrient is exhausted, their growth stops and eventually they die.

These types of cultures typically last for about one week These types of cultures typically last for about one week. After that, if you wish to continue the culture you must "subculture“ by adding some cells from the old culture into a flask containing fresh growth medium. The batch culture is most common culture system, due to its simplicity and low cost

The size of the inoculum Upscaling algal culture The upscaling of pure strains of selected species of microalgae starts from small containers (0.5 ml) and proceeds through various steps up to the mass production in polyethylene (PE) bags (up to 450l) or tanks (1 000 l and up). The size of the inoculum The volume of the algal inoculum is usually 15 to 20% of the new volume.

Fig 1. A typical scheme of a batch type production

Inoculation of a PE bag from a flask or from another bag Prepare the bag, either suspended to a rack or placing it inside a cylindrical frame made of wire. Fill the bag with sterilized water; leaving enough free space for the volume to be inoculated. Fit two PVC tubes for aeration to the bottom of the bag, connect them to an air line and adjust the air flow to a gentle bubbling. Add the nutrients using a graduated cylinder at the usual rate of 1 ml/l of each working solution. تأكد من عدم وجود التسريبات

Select a mature culture that will be used as inoculum, either from a large flask or from another bag. In case a flask is used as inoculum, pour the algal culture from the flask into the bag. The inoculum should be about 15% of the receiving volume. If the inoculum comes from another bag, the volume to be transferred should be about 15-20% of the receiving volume On each bag mark date, algal species, origin of the inoculum (bag or flask) and the bag serial number. To reduce the risk of contamination, smaller bags are usually inoculated from flasks, whereas larger bags are inoculated from smaller bags.

Photos of Large volume cultures

Continuous Culture This method of culturing algae differs from the batch culture method in that fresh medium is added to the culture at a constant rate and old media (and some of the algae cells) is removed at the same rate. The culture therefore never runs out of nutrients.

As you can imagine the glassware and tubes for this type of system are much more complex than the simple batch culture. For most classroom exercises the batch culture system should do the job, however if you should ever need a constant supply of cells this system is the best.

Parts of a Continuous Culture System The diagram below show the parts of a continuous culture system.

First, fresh growth medium is stored in the large vessel. Air is pumped into the airspace in this medium vessel. This air pressure will push the medium through a tube which is connected to the culture vessel. clamp allow add medium to the culture vessel. Air is also pumped into the culture vessel through a sterile filter. This air passes down a long glass tube to the bottom of the culture and bubbles up.

This bubbling air has three effects: It supplies CO2 to the culture. Aids in circulation and agitation of the cultures. Pressurizes the head space of the culture vessel so as to provide the force to "remove" an amount of media (and cells) equal to the volume of inflowing media.

There is one other glass tube in the culture vessel, the sample port . The air flowing into the culture vessel flows out through an outflow tube . As fresh medium is added to the culture vessel the level of the liquid in the culture vessel rises. When that level reached the bottom of the outflow tube old medium and cells flow out of the culture vessel into a waste flask . There is one other glass tube in the culture vessel, the sample port . When you need a sample of cells from the culture vessel you open up the clamp on the sample port and medium and cells flow out. When you have enough you re-close the sample port.

Semi-Continuous System In a semi-continuous system the fresh medium is delivered to the culture all at once. Fresh medium flows into the culture vessel, and spent culture flows out into a collecting vessel.