Agar Agar – Asset Of Microbiologist

 

Agar, also known as agar-agar, is a jelly-like substance made up of polysaccharides extracted from the cell walls of various red algae, primarily ogonori (Gracilaria) and "tengusa" (Gelidiaceae). Agar is composed of two components: the linear polysaccharide agarose and a heterogeneous mixture of smaller molecules known as agaropectin. The agarose makes up about 70% of the mixture. Agarose is a linear polymer composed of repeating agarobiose units, a disaccharide composed of D-galactose and 3,6-anhydro-L-galactopyranose. Agaropectin is a heterogeneous mixture of smaller molecules found in lower concentrations. It is composed of alternating units of D-galactose and L-galactose that have been heavily modified with acidic side groups such as sulphate and pyruvate. The mixture forms a supporting structure in the cell walls of certain algae species and is released when heated. Agarophytes are algae that belong to the Rhodophyta (red algae) phylum. The agaropectin is removed during the processing of food-grade agar, and the commercial product is essentially pure agarose.

Agar has been used in Asian desserts as well as a solid substrate in culture media for microbiological work. Agar can be used as a laxative, an appetite suppressant, a vegan substitute for gelatin, a thickener for soups, in fruit preserves, ice cream, and other desserts, as a clarifying agent in brewing, and for sizing paper and fabrics.

The use of agar as a solid medium for growing different microbes first began in the late 19th century. On the suggestion of his wife, Fanny Hesse, the German microbiologist Walther Hesse, an assistant working in Robert Koch's laboratory, described agar for use in microbiology in 1882. Because of its higher melting temperature, agar quickly supplanted gelatin as the base of microbiological media, allowing microbes to be grown at higher temperatures without the media liquefying. After this, agar production quickly increased due to its newfound use in microbiology.

Why Is Agar Used in Microbiology?

Agar demonstrates hysteresis, solidifying at approximately 32–40°C but melting at 85°C. This property provides an appropriate balance of easy melting and good gel stability at relatively high temperatures. Because many scientific applications necessitate incubation at temperatures close to that of the human body (37 °C), agar is preferable to other solidifying agents that melt at this temperature, such as gelatin.

Agar plate

An agar plate or media petri plate is a type of growth medium that contains agar and other nutrients and is used to culture and observe microorganisms such as bacteria and fungi. Because agar is indigestible to many organisms, microbial growth has no effect on the gel, which remains stable. Agar is typically sold commercially as a powder that, like gelatin, can be mixed with water and prepared before use as a growth medium. Other ingredients are added to the agar to meet the microbes' nutritional needs. Because some microbes prefer certain environmental conditions over others, many microbe-specific formulations are available. Agar is frequently dispensed with the aid of a sterile media dispenser.

Motility assays

Since agar or agarose medium is porous, it can be used to assess microorganism motility and mobility. Because the porosity of the gel is proportional to the concentration of agarose in the medium, different levels of effective viscosity can be chosen depending on the experimental objectives.

A common identification method involves culturing an organism sample deep within a block of nutrient agar. Cells will try to grow inside the gel structure. Non-motile species will grow only along the now-empty path introduced by the invasive initial sample deposition, whereas motile species will be able to migrate, albeit slowly, throughout the gel, and infiltration rates can be visualized.

Another method for measuring chemotaxis and chemo-kinesis is the under-agarose cell migration assay, which involves placing a layer of agarose gel between a cell population and a chemoattractant. As a concentration gradient develops from the chemo-attractant's diffusion into the gel, various cell populations requiring different levels of stimulation to migrate can then be visualised using microphotography over time as they tunnel upward through the gel against gravity along the gradient.

Agar Agar Type I

Agar AgarType I was developed by TM Media for use in routine bacteriological laboratory work, plant tissue culture media, and pharmaceutical preparations where clarity and compatibility are not critical. It swells but does not dissolve when suspended in cold water. However, it dissolves easily in boiling water, and soaking the powder in cold water improves its solubility. The powder is freely soluble in hot water at temperatures above 85 °C.

TM Media offers a wide range of Biological Media Bases of both animal and non-animal origin. Along with Biological Media Bases, TM Media also provides Dehydrated Culture Media and Ready-to-Use Culture Media in a variety of packaging such as plates, bottles, slants, broth, and bags that can be chosen depending on the experimental objectives.