Downloaded from www.microbiologyresearch.org by IP: 54.70.40.11 On: Fri, 08 Mar 2019 21:58:59 Journal of General Microbiology (1988), 134, 387-393. Printed in Great Britain 387 Arachidonic Acid from Fungi Utilizing Fatty Acids with Shorter Chains as Sole Sources of Carbon and Energy ByS. S. RADWAN*Y AND ARWA H. SOLIMAN Department of Botany, Faculty of Science, Ain Shams University, Abbassia, Cairo, Egypt (Received 2 June 1987; revised I1 September 1987) Several species of soil fungi, belonging to the genera Aspergillus, Penicillium, Fusarium, Paecilomyces, Trichoderma, Cladosporium and Stachybotrys could utilize caprylic, myristic, palmitic, stearic and oleic acids, as well as their sodium salts, as sole sources of carbon and energy. None of the fungal isolates showed any particular specificity to a given fatty acid. Only the caprylic acid utilizers grew poorly, otherwise the growth was fair to abundant. The optimal fatty acid concentration for fungal growth was 10 g 1-l. Growth yields were comparable with those on glucose. The optimal pH values were in the region of neutrality and the isolates could tolerate high acidity. Lipids from fungi grown on fatty acids or their sodium salts contained free fatty acids as the predominant lipid class. Such lipids were much richer in arachidonic acid than those from the same fungi grown on glucose. Fungi that contained the highest levels of arachidonic acid were those grown on myristic and palmitic acids, namely Aspergillus versicolor and Aspergillus ustus, respectively. INTRODUCTION There are very few studies on the microbial degradation of individual fatty acids in sewage (for a relevant review see Harp, 1979). Moreover, there are no systematic studies on micro- organisms that can utilize fatty acids as sole sources of carbon and energy. The objectives of the present paper were to provide this information and to investigate the influence of fatty acids on the lipid composition of the micro-organisms utilizing them. Particular emphasis has been placed on the production of arachidonic acid (20:4) by fatty acid utilizing organisms. METHODS Fatty acids. Caprylic (8 : 0), myristic (1 4 : 0), palmitic (16 : 0), stearic (18 : 0) and oleic (1 8 : 1) acids were purchased from Merck. Sodium salts of these fatty acids were prepared by saponification with NaOH following established procedures (Christie, 1973). Biodegradation offatty acids. Suspensions of a garden soil sample and a desert soil sample were prepared by shaking 1 kg of each sample in 1 1 sterile water for 15 min. After standing for 1 h, the supernatant was decanted and 100 ml samples were dispensed into 500 ml Erlenmeyer flasks. For control experiments, flasks containing soil suspensions were sterilized by autoclaving at 120 "C for 20 min. Each flask was provided with 100 mg of a fatty acid or its sodium salt and incubated at 30°C. Flasks were assayed after 6, 12 and 24 weeks to detect any undegraded fatty acids. Suspensions that had received sodium salts of fatty acids were first acidified with 6 M-HCl to release the fatty acids. Undegraded fatty acids were recovered by extracting three successive times with diethyl ether. The recovered fatty acids were dried, weighed and tested for purity by TLC. Isolation offatty acid utilizers. Micro-organisms capable of utilizing fatty acids as sole sources of carbon and energy were isolated on a basal medium supplemented with 250 mg 1-l of one fatty acid (dissolved in diethyl ether, which was evaporated leaving the acid dispersed in the medium) or its sodium salt. The fatty acids remained insoluble in the medium whereas the sodium salts were soluble, but only at neutral to alkaline pH values. The basal medium contained (1-l): 1.0 g KH,PO,; 3.0 g NaCl; 0.25 g MgS0,.6H20; 1.0 g NaHCO,; 0.5 g (NH,),SO,; 1.Og KNO,; 0.25g CaC12.HzO; 0.1 mg FeS0,.7H20; 0.1 mg CuS0,.5H20; 0.1 mg ZnC12.6H,0; 0-5 mg t Present address : Chairman, Department of Botany and Microbiology, Faculty of Science, Kuwait University, PO Box 5969, 13060 Safat, Kuwait. 0001-4214 0 1988 SGM