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Anthraquinones and Phenols as Intermediates in the Formation of Dark-Colored, Humic Acid-Like Pigments by Eurotium echinulatum¹

ABSTRACT

Eurotium echinulatum, a fungus isolated from a vertisol in southern Spain, formed humic acid-like pigments during growth in glucose-asparagine or glucose-NaNO₃ media. After 6 to 7 days the phenols, orsellinic, p-hydroxycinnamic, and p-hydroxybenzoic acids, and the anthraquinones, endocrocin, emodin, and physicion were detected in the culture media. Upon further development of the mycelial mats additional aromatic compounds were produced and after 4 to 6 weeks more than 50 different ether-extractable phenols and anthraquinones were detected. With further incubation the amounts and number of these compounds decreased and pigment formation in the media increased. After 2 to 3 months the culture media were dark brown to black and about 1 to 3.5 g/liter of polymer could be recovered upon acidification of the culture medium. Sodium amalgam reduction of this polymer yielded numerous phenols, anthraquinones, anthrones, and possibly anthracene derivatives. Treatment with sodium dithionite yielded largely anthraquinones. The polymer contained 1 to 4.5% N depending upon the N source. From 50 to 60% of this N was released in the form of amino acids upon acid hydrolysis. With both asparagine and NaNO₃ as N sources the same amino acids were isolated from 6N HCl hydrolysates. Quantitatively, however, there were differences in the percentage distribution of the amino acids.

¹ Contribution from the Institut für Biochemie des Bodens Forschungsanstalt für Landwirtschaft, Braunschweig, Germany, Centro de Edafologia y Biologia Aplicada del Cuarto, Sevilla, Spain, and the Dept. of Soil Science & Agric. Eng., Univ. of California, Riverside CA 92502. The authors give thanks to Prof. Dr. Steglich, Berlin; Prof. Dr. K. Wagner, Munich; and Prof. Dr. M. H. Zenk, Bochum, for furnishing pure anthraquinone samples. They thank Mrs. E. Pleiss for skilled technical laboratory assistance and Prof. Dr. H. Söchtig for his help with the quantative amino acid determinations. C. Saiz-Jimenez thanks the Deutsche Forschungsgemeinschaft for a post-doctoral stipend.

² Visiting Scientist at the Inst. of Soil Biochemistry, Biochemist, and Professor of Soil Science, Univ. of California, Riverside, respectively.

Received for publication November 11, 1974. Accepted for publication January 30, 1975.