Agar

As it appeared in the article Red Algae for Pure Cultures.

Introduction

This excellent article appeared in the “Off the Bench,” a feature in The EppoendorfLifeScienceStyle Magazine. It is an excellent magazine with editorial quality of the highest order. I am delighted to come across it and it gives me great pride to quote their article in its entirety.

Red Algae for Pure Cultures (as it apeared in The EppoendorfLifeScienceStyle Magazine)

“Agar-agar, the basic substance for nutrient solutions, has long been established as an indispensable material in the field of microbiology. However, certain species of red algae, the raw material for bacteriologic agar-agar, is now threatened with extinction. Laboratories are increasingly forced to look for alternatives. 

On March 24, 1882 Robert Koch of Berlin University announced a scientific sensation. The bacteriologist was the first researcher to identify the causative agent of the menacing tuberculosis epidemic which was raging at the time: the rod-shaped bacterium Mycobacterium tuberculosis. This discovery laid the foundation for Koch’s subsequent world-wide fame, and it earned him the Nobel Prize for Medicine and Physiology in 1905.

The ideal gelling agent

One substance that made a significant contribution to the medical breakthrough in tuberculosis research was completely new to the laboratory at the time: agar-agar (short: agar). In order to be able to study the causative agent of the “white plague”, Koch had to isolate the bacterium and grow it as a pure culture in a petri dish. He initially used nutrient solutions from meat broth that were solidified with gelatin. The problem was that this mixture would melt between 26 and 30 degrees Celsius. To make matters worse, gelatin is degraded and liquefied by a number of bacterial enzymes. For this reason, agar is now, as it was then, the alternative of choice in the laboratory: the complex polysaccharide (sugar polymer) which is extracted from the cell walls of certain red algae cannot be degraded by bacteria. In addition, agar does not melt until it reaches 100 degrees Celsius and remains liquid while cooling down to a temperature of approximately 45 degrees Celsius. At room temperature, it forms a semi-solid, translucent gel. Organisms are immobilized on the surface or inside the mass, leaving them to form colonies on or inside the gelled nutrient. In this way, pure cultures may be generated in order to obtain small amounts of microorganisms for subsequent studies.

From pudding to petri dish

The idea to use agar in the laboratory setting, however, did not originate with Robert Koch himself but rather with the German-American Fanny Hesse. She was married to the physician and microbiologist Walther Hesse, a colleague of Koch’s. When she was a young woman in New York, a neighbor who hailed from Indonesia first mentioned to her the special properties of the substance. Fanny Hesse subsequently used agar for her puddings that now remained firm even at warmer temperatures. This was what later inspired her husband in Germany to use this substance obtained from red algae for his nutrient broths.

The purely plant-based agar had long been established as a thickener in Asia. The name originates from the Malayan language family and translates into something along the lines of “gelling food from algae”. The substance is especially suitable as a sauce thickener in warmer regions as well as for solidifying jams, cake glazes, fruit sauces, ice creams, puddings and also fruit puddings.

Shrinking algae populations

Besides Japan, where agar has been known since the 17th century, red algae are now primarily harvested in Chile, Spain and Morocco. Together, these countries yield two thirds of all globally traded raw agar. In former times, the algae from which agar is purified were simply collected from beaches at low tide, but today, many areas no longer harbor sufficient wild red algae. With population growth and increasing demand for vegetarian foods, the coveted material is experiencing increasing scar­city worldwide. In addition, pilot experiments are under way which explore the future use of agar as a fully biodegradable substitute for plastic.

Since the natural resources no longer meet today’s global demand, fewer of the coveted red algae are now harvested from the wild, but are cultivated instead. This, however, does not work well for all species of the plant. An especially sensitive example is the red algae species Gelidium sesquipedale, the source of the highly purified agar used in the laboratory. This unique species of red algae not only features excellent properties (see information box), but it also places high demands on its natural environment: in order to grow, it requires a rocky ocean floor as well as cold, current-rich waters with plenty of oxygen. This is why, so far, all attempts at growing this particular species of red algae in aqua­cultures have failed.

Threatened with extinction

In Chile, which exports roughly 1,800 tons of raw agar annually, red algae are actually facing extinction. “The natural populations have almost completely vanished”, says Alejandro Buschmann, Director of the Oceanographic Research Institute in the Southern Chilean city of Puerto Montt. Instead of simply collecting the algae from the coast, as was the traditional practice, the plants now need to be seeded on the beach in order to be harvested later, in strictly regulated amounts. In Morocco, too, the naturally occurring red algae populations are acutely endangered.

This is the reason the North African country enforced drastic export restrictions in late 2015. As a result, prices have skyrocketed. The scarce supply has further led to the consequence that some manufacturers of laboratory products have been unable to deliver certain agar products. As a result, some laboratories have turned to alternative gelling agents, such as guar gum, tragacanth or ground psyllium husks. Steve Petrovski and Daniel Tillet of La Trobe University in Melbourne were also searching for an affordable solution and decided on common agar, the food additive known as E406. It is also extracted from red algae, but in comparison with bacteriological agar supplied by laboratory vendors, it is much more reasonably priced.

The two Australian microbiologists cultivated 50 species of bacteria on the high quality agar as well as on the significantly cheaper food agar. The result: in terms of shape and structure, as well as in terms of growth rates and vitality of the colonies, no differences could be detected between the nutrient media.

For this reason, Petrovski and Tillet have switched entirely to food agar for their routine experiments and were able to reduce the cost for nutrient media by 80 percent.

The Original Article

http://web.eppendorf.com/off-the-bench/agar_agar.html

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