176 PROVASOLI [CHAP. 8 



solutes from 10 to 45% of the total organic matter produced (Allen, 1956; 

 measured as organic material oxidizable by dichromate). The products formed 

 include polysaccharides, gly colic, oxalic and pyruvic acids and only traces of 

 organic nitrogen. Fifteen species of fresh-water Chlamydomonas, two Chloro- 

 sarcina and one Gloeocytis liberate in the medium 10-115 mg/1. of soluble 

 polysaccharides. This excretion constitutes 2 to 25% (Chlamydomonas mexicana) 

 of the total organic matter produced (Lewin, 1956). The main components of 

 the polysaccharides (precipitated by ethanol and hydrolyzed with H2SO4) are 

 galactose and arabinose for all species except C. ulvaensis (glucose and xylose). 

 The associated sugar moieties are fucose, rhamnose, mannose, uronic acids and 

 several unidentified components (identification by chromatography). 



Allen found that the production of extracellular compounds parallels growth, 

 i.e. the substances are released by living and dividing cells ; the same applies to 

 C. parvula (Lewin, 1956) and Anabaena cylindrica (Fogg, 1952); however, 

 production of mucilage around the cells continues in old cultures, reaching 40- 

 60% of the total organic matter produced (Chlamydomonas parvula and C. 

 peterfii) (Lewin, 1956). 



Also unicellular marine algae, in bacteria-free culture, excrete large amounts 

 of "carbohydrates" (Table III). These results were obtained with the A^-ethyl 

 carbazole hydrolyzing method, which gives a purple-red coloration with carbo- 

 hydrates ; optical densities were converted to glucose equivalents, except for 

 Prorocentrum sp. (arabinose equivalent). Guillard and Wangersky (1958) 

 found that excretion of carbohydrates does not parallel growth : it is very low 

 and does not exceed 3 mg/1. during exponential growth. Carbohydrates accumu- 

 late in the medium at or right after maximum growth (10 6 -10 7 cells/ml). This 

 accumulation may come from lysis of dead cells or a modified metabolism 

 when division is hampered by nutritional deficiencies but photosynthesis is 

 active ; Navicula pelliculosa only under these conditions makes huge amounts 

 of capsular polysaccharides (J. C. Lewin, 1955). 



Not all marine organisms behave similarly : multiplying Katodinium dor- 

 salisulcum produces a polysaccharide mucilage (McLaughlin et al., 1960), so 

 much so that mucoid masses form ; in stationary cultures they float to the top 

 because of entrapped bubbles of photosynthetic oxygen. When growth has 

 reached an optimal cell concentration (10 4 cells/ml), the cells keep producing 

 polysaccharide until the medium gels (1.4-2.6 g/1. of polysaccharide are 

 produced in a month). Hydrolysis of the polysaccharide yielded glucose, 

 galactose and fructose. The supernatant of Katodinium was the only one 

 to give a carbazole reaction typical of sugar (purple) ; the supernatants oiMono- 

 chrysis lutheri and Prymnesium parvum gave different colors, respectively 

 straw-green and light green. Guillard and Wangersky (1958) report for the 

 same strains of these organisms, and with the same reagent, a good production 

 of "carbohydrates" (Table III). They do not mention any discrepancy of the 

 color reaction, yet they (Wangersky and Guillard, 1960) noted a different 

 color reaction (blue) obtained with the A 7 -ethyl carbazole method in Amphi- 

 dinium carteri supernatants. This filtrate gave the usual purple carbohydrate 



