ARS | Publication request: Production of arachidonic acid and dihomo-gama-linolenic acid from glycerol by oil-producing filamentous fungi, Mortierella in ARS Culture Collection

Submitted to: Journal of Industrial Microbiology and Biotechnology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 10, 2008
Publication Date: June 10, 2008
Citation: Hou, C.T. 2008. Production of arachidonic acid and dihomo-gama-linolenic acid from glycerol by oil-producing filamentous fungi, Mortierella in ARS Culture Collection. Journal of Industrial Microbiology and Biotechnology. 35:501-506.

Interpretive Summary: Recently, production of biodiesel from vegetable oils has become the U.S. national priority program. During the production of biodiesel, a huge amount of co-product glycerol will be produced. To find a new use of this co-product glycerol becomes equally important. Polyunsaturated fatty acids (PUFAs) play important roles in human health. Arachidonic acid (AA) is an important PUFA. (AA)-producing filamentous fungus, Mortierella alpine is used commercially to produce AA and another PUFA, dihomo-gamma-linolenic acid (DHLA) from glucose. In our study, we screened 12 filamentous fungi, Mortierella from ARS Culture Collection and found that they can also use glycerol as substrate to produce biologically active PUFAs such as AA and DHLA. Two strains: M. alpina and M. Zychae were the best producers of AA and DHLA. The yields obtained are as good as that using glucose substrate indicating that glycerol can be used to substitute glucose as industrial scale production substrate. This finding establishes a new use of bioglycerin, leading to reduction of biodiesel production cost and benefits both U.S. farmers and the public.

Technical Abstract: Twelve Mortirella strains: M. alpina NRRL 6302, M. claussenii NRRL 2760, M. elongata NRRL 5246, M. epigama NRRL 5512, M. humilis NRRL 6369, M. hygrophila NRRL 2591, M. minutissima NRRL 6462, M. multidivaricata NRRL 6456, M. nantahalensis NRRL 5216, M. parvispora NRRL 2941, M. sepedonioides NRRL 6425, and M. zychae NRRL 2592 were screened for their production of arachidonic acid (AA) and dihomo-gamma-linolenic acid (DGLA). All of the strains tested produced AA and DGLA from glucose. In anticipation of huge production of co-product glycerol from national biodiesel program, these 12 strains were screened for their production of AA and DHLA from glycerol. All the strains tested grew on glycerol and produced AA and DGLA except M. nantahalensis NRRL 5216, which could not grow on glycerol. The amount of AA and DGLA produced are compatible with those obtained with glucose-grown mycelia. Judging from their AA production and yields of CDW, and total fatty acids from glycerol, we selected two strains, M. alpina and M. Zychae for further studies with glycerol substrate. Glycerol concentration of 0.5% to 4% produced the best cells dry weights and AA production for both strains. Higher substrate concentration inhibited the cells growth. Effect of pH on the growth and AA content was studied from 5 to 7.5. M. zychae had an optimum pH for both the cell growth and the production of AA at around pH 6.0. At pH higher than 7.0, zychae cells still produce AA however, their mycelia weight were decreased. At lower pH media, the cells grow and produce AA at a slightly reduced value. The effect of pH was not significant with M. alpina at the pH ranges tested. The best temperature and rpm for both strains on cells growth and AA production were at 28 deg C and 120 rpm. DGLA productions were in most cases about 1/4 to 1/3 of AA. Time course studies of both strains alpina and zychae grow on glycerol showed that AA production increases steadily up to 360 hours, and reach at 28.68 and 34.53 mg per g dry cell weight, respectively. Strain alpina grows poorer and produces less AA than zychae on glycerol substrate. Therefore, glycerol can be considered for industrial use in the production of AA and DGLA.