Growth and Oxygen-Uptake Responses of Cunninghamella Echinulata on Even-Chain Fatty Acids

SUMMARYAt alkaline pH values (8.0 and 7.2) the long-chain (C14-C18) and short-chain (C2-C8) fatty acids served as sole sources of carbon for Cunninghamella echinulata, while laurate and caprate were not utilized. Only caprate failed to provide for growth at pH 6.5. When the initial pH was lowered to 5.5, caprate served for growth, as did all longer even-chain acids and acetate, but butyrate, caproate, and caprate were not utilized. Oxygen-uptake responses of C. echinulata on the even-chain fatty acids (C2-C18) were, in general, similar to the growth responses. However, laurate and caprate were inhibitory at all the pH values tested (8.0, 7.2, 6.5, and 5.5), and myristate was stimulatory only at pH 5.5. The short-chain acids (C2-C8) yielded oxygen uptakes above endogenous levels at alkaline pH values (8.0 and 7.2) but were inhibitory at acidic pH. values (6.5 and 5.5). In addition, palmitate, which never failed to serve as a growth substrate, gave uptakes slightly below the endogenous level at pH 8.0. Analyses of the growth and respiratory data indicate that the non-dissociated acid is the permeant molecular form in the case of the short-chain acids (C2-C8), and that the degree of inhibition increases with the carbon-chain length. In solutions of the longer-chain-length compounds (C10-C18), the conjugate base appears to be the permeant form, and the degree of inhibition decreases as the chain-length increases.