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Galactomyces geotrichum MK017: in silico Model of Succinic Acid Metabolic Pathway
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1  Department of Food Chemistry and Instrumental Analysis, Institute of Food Technology Poznań University of Life Sciences, Poznań, Poland


Galactomyces geotrichum MK017 is an anamorphic and non-pathogenic fungus-like yeast included in Hemiascomycetes that was isolated from raw-milk and is widely used as adjunct culture in the maturation of cheese like raclette, münster, limburger, cottage cheese and sheep cheese [1]. Succinic acid (C4H6O4), also known as amber acid, butanedioic acid or butanedicarboxylic acid, is precursor of numerous pharmaceuticals and chemicals including adipic acid, 1,4-butanediol, tetrahydrofuran, N-methyl pyrrolidinone, 2-pyrrolidinone, succinate salts, gamma-butyrolactone and biodegradable polymers. Galactomyces geotrichum MK017 produce metabolic products by fermentation such as succinic acid and acetic acid from glucose and others such as ethanol, formic acid, lactic acid [2]. The central carbon metabolism of Galactomyces geotrichum MK017 and its metabolic network is analyzed and integrated by combining biochemical and physiological information. Metabolic flux analysis (MFA) as powerful methodology was used for calculation of the intracellular fluxes by using a stoichiometric model (metabolic pathway map) for the major intracellular reactions and mass balances around intracellular metabolites. A set of measured rates of substrates and metabolites was used for the calculations [3, 4]. The metabolic flux map or diagram of the biochemical reactions include production of pyruvate and phosphoenolpyruvate carboxylation pathways examined in the case of succinic acid production in G. geotrichum MK017. In silico succinic acid pathway was compared with experimental succinic acid pathway of G. geotrichum MK017. The resulting flux distributions were visualized and analysed, and the simulation parameters were adjusted until the model correctly predicted the phenotype. Simulations were used to form hypotheses and predict the yields of in silico succinic acid pathway. The predictions were then validated experimentally.

[1] Mało poznany grzyb pleśniowy Galactomyces geotrichum w wyrobach mlecznych, A. Grygier, K. Myszka, M. Rudzińska, P. Spozywczy, 5, 2016.
[2] Purification and characterization of an extracellular lipase of Galactomyces geotrichum, A. Phillips, G.H. Pretorius, G.H. van Rensburg, Biotechnology letters, 13(5), 1979.
[3] In Silico Metabolic Pathway Analysis and Design: Succinic Acid Production by Metabolically Engineered Escherichia coli as an Example, S.Y. Lee, S.H. Hong, S.Y. Moon, Genome Informatics 13(9), 2002.
[4] The Metabolic Pathway Engineering Handbook: Fundamentals, Ch. D. Smolke, CRC Press USA, 2010.

Keywords: Galactomyces geotrichum MK017, succinic acid pathway, metabolic flux analysis