Abstract
Submerged-culture techniques have given growth of the mycobionts Cetraria islandica and Cladonia papillaria satisfactory for metabolic and chem- ical studies. Special apparatus for inoculation, metabolic studies, and culture maintenance is described. In conjunction with biosynthetic studies on (+)- protolichesterinic acid (PLA), the metabolic rates of both organisms, in both the lichenized form as well as separately in culture, were found satisfacory for tracer studies. Using hydroponic administration of 10% glucose solution, sodium (114C) acetate was shown to be incorporated into PLA by lichenized C. islandica, but by neither mycobiont in submerged culture. A gas-chromatographic tech- nique is described for the analysis of PLA, which was found absent in both mycobionts under the culture conditions used. The symbiotic relationship of lichens presents unique possibilities for biochemical study. In particular, lichens produce a host of aliphatic acids formally related to the citric acid and fatty acid cycles. Examples are caperatic acid, rangiformic acid, proto- lichesterinic acid (PLA), lichesterinic acid (LA), nephrosterinic and nephrosteranic acid, nephromopsic acid, and roccellic acid. (For a review, see Asahina & Shibata, 1954.) The occurrence of this class of compound is rare in other organisms, though agaricic acid in Polyporus officinalis (Thomas & Vogelsang, 1907) and 2-decylcitric acid in Penicillium spiculisporum (Culberson, 1969) are worthy of mention. It appears that the recently discovered acaranoic and acarenoic acids (Santesson, 1967) are biosynthetically related to this class. Studies on PLA were of particular interest to us because of 1) their possible value in demonstrating a biochemical link between the citric acid and the fatty acid cycles, 2) the reputed antibiotic properties of PLA (Sticher, 1965), 3) the ready availability of PLA, 4) the availability of field-collected plants and of pure cultures of the mycobionts of PLA-producing lichens (Cetraria islandica, Cladonia papillaria), and 5) the probable ease of both the chemical degradation of PLA and of the synthesis of the hypothetical precursors of this substance. In stationary liquid cultures, tracer quantities of sodium (114C) acetate were
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