Chapter 55 



Proposals on the Classification of Micro- 

 organisms Which Utilize the Polysaccharides 

 of Marine Algae and a Definition for Agar 



W. Yaphe 



0, 



lie of the problems involved in the study of the bacteria which 

 utilize the polysaccharides of marine algae is the characterization 

 of the algal preparations. The terms agar, carrageenan, funorin 

 are used to describe extracts obtained from the Rhodophyceae 

 and alginic acid; fucoidin, those obtained from the Phaeophyseae. 

 Recent chemical studies have shown that these words do not 

 refer to single substances but rather to mixtures of polysac- 

 charides. 



These polysaccharides are only found in marine plants. It is 

 thus not surprising that the bacteria which can decompose them 

 are present in relatively high numbers in the sea and are only 

 occasionally isolated from the soil. The bacteria which decompose 

 agar and alginic acid have been extensively investigated. This 

 work can now be interpreted with reference to the new infonna- 

 tion, now available, on the structure of these polysaccharides. 



Agar 



The word agar-agar is used to describe any gelatinous 

 material obtained from a number of different red algae. In 1881, 

 the gel from Eucheuma sp. was used to prepare bacteriological 

 media. A few years later, a material of lower viscosity and higher 

 gel strength was obtained from Japan. This agar was prepared 

 mainly from Gelidium sp. but it also contained the extracts from 

 as many as 34 different species of red algae ( 12 ) . The Japanese 

 product was the main world source of agar up until 1939. Since 

 then, agars have been prepared in a number of different countries. 

 In most cases, the commercial products are sold under a trade 



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