Honda, Yoichi

Tsuda, Saeko

Watanabe, Takahito

Watanabe, Takashi

Kyoto University Research Information Repository

TitleUnsaturated fatty acids in selective lignin degradation by thewhite-rot fungus, Ceriporiopsis subvermispora(RECENTRESEARCH ACTIVITIES)Author(s)Watanabe, Takahito; Tsuda, Saeko; Honda, Yoichi; Watanabe,TakashiCitationSustainable humanosphere : bulletin of Research Institute forSustainable Humanosphere Kyoto University (2007), 3: 2-2Issue Date2007-08URL http://hdl.handle.net/2433/51017RightType Departmental Bulletin PaperTextversionpublisherKyoto UniversityRECENT RESEARCH ACTIVITIESUnsaturated fatty acids in selective lignin degradation by the white-rot fungus,Ceriporiopsis subvermispora(Laboratory of Biomass Conversion, RISH, Kyoto University)Takahito Watanabe, Saeko Tsuda, Yoichi Honda and Takashi WatanabeUnsaturated fatty acids (UFAs), such as linoleic acid (18:2n-6) and a-linolenic acid (18:3n-3), havecrucial roles as structural components of biological membranes, cellular energy source, and cell signalingmolecules. UFAs in phospholipids increase the membrane fluidity necessary to maintain the properfunction of biological membranes. In the biosynthesis of UFAs, fatty acid desaturases are key enzymesthat are responsible for the insertion of double bonds into alkyl chains, following the abstraction of twohydrogen atoms. These enzymes are almost universally found in microbial, plant, and animal cells, wherethey play important roles in a wide range ofphysiological processes.It is well known that many poikilothermic organisms adapt to cold temperatures by increasing fatty aciddesaturation to restore the fluidity of cold-rigidified membranes. Moreover, it have been graduallyrevealed that fatty acid desaturase genes are inducibly expressed by the ability of membrane-boundedproteins to sense a decrease in membrane fluidity generated either by a· temperature downshift or byrestricted availability ofUFAs [1] [2].In a budding yeast Saccharomyces cerevisiae, OLE], encoding a ~9-fatty acid desaturase to insert adouble bond into the ~9 position at stearic acid (18:0) and palmitic acid (16:0), is highly expressed duringethanol fermentation as well as under lower temperatures. The higher OLE] expression leads to increasesin fatty acyl chain length and the proportion of UFA [3] [4]. These observations suggest that fatty aciddeaturases may be inducibly expressed in the physical and chemical stress conditions, which drasticallyalter the membrane fluidity.A selective lignin-degrading fungus, Ceriporiopsis subvermispora, can selectively degrade ligninwithout intensive damage of cellulose. We have demonstrated that extracellular lipid peroxidation bymanganese-dependent peroxidase (MnP) occurred in the selective lignin degradation by C. subvermispora.At an incipient stage of cultivation on extractive-free wood meal cultures, this fungus produced MnP andlarge amounts of linoleic acid and palmitic acid, and MnP oxidized them to aldehydes. In prolongedcultivation period after 2-weeks, however, the amount of these fatty acids decreased with increasingorganic hydroperoxide and the accumulation of lipid peroxidation products reacting with thiobarbituric acid(TBARS) in organic extracts from wood meal cultures. These observations suggest that UFAs might actas a precursor of lipid peroxidation that is a key reaction of the selective lignin degradation [5].Because lipid peroxidation is the process whereby free radicals abstract electrons from the lipids, it isvery likely to damage cell membranes of C. subvermispora even if lipid peroxidation takes placeextracellularly. Moreover, exposure to free radical species generated by lipid peroxidation and aldehydesproduced by MnP may lead to induce the expression of fatty acid desaturase genes. Therefore, we focuson the molecular relationship between lipid peroxidation and the biosynthesis of UFA, and we successfullycloned fatty acid desaturase genes from C. subvermispora. We are now trying to study biochemical andgenetic bases of fatty acid desaturases and lipid-related metabolites involved in the selective lignindegradation by C. subvermispora.REFERENCES[1] Suutari, M. and Laakso, S. (1994) Crit. Rev. Microbiol., 20: 285-328.[2] Aguilar, P. S. and de Mendoza, D. (2006) Mol. Microbiol., 62: 1507-1514.[3] Kajiwara, S., Aritomi, T., Suga, K., Ohtaguchi, o. and Kobayashi, O. (2000) Appl. Microbiol.Biotechnol., 53: 568-574.[4] Yamada, T., Shimoi, H. and Ito, K. (2005) J. Biosci. Bioeng., 99: 512-516.[5] Enoki, M., Watanabe, T., Nakagame, S., Koller, K., Messner, K., Honda, Y. and Kuwahara, M. (1999)FEMS Microbiol. Lett., 180: 205-211.2

Unsaturated fatty acids in selective lignin degradation by the white-rot fungus, Ceriporiopsis subvermispora(RECENT RESEARCH ACTIVITIES)

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Unsaturated fatty acids in selective lignin degradation by the white-rot fungus, Ceriporiopsis subvermispora(RECENT RESEARCH ACTIVITIES)

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