Fungal screening for biological removal of extractives fromEucalyptus globuluswood

Abstract

Wood extractives cause production troubles during pulp and paper manufacture. The potentiality of fungal strains for biotechnological removal of extractives from Eucalyptus globulus Labill. wood is evaluated here. First, a survey of fungi present in eucalypt woodlands in western Spain was carried out, and 90 species, including fungi strictly associated with eucalypt trees, were collected. Then, a total of 33 basidiomycetes, 21 ascomycetes, and 19 conidial fungi (including some strains from culture collections) were compared in terms of their capacity to decrease the acetone extract of eucalypt wood. High extractive removal (50-70% of initial content) was obtained with Ophiostoma, Mollisia, and Pleurotus species, as well as with Funalia trogii (Berk. in Trog) Bond. & Singer, Melanotus hepatochrous (Berk.) Singer, and Paecilomyces sp. Microscopic observation of the degraded wood revealed a correlation between extractive degradation and removal of spherical deposits in wood rays. Moreover, when extractive biodegradation was analyzed by gas chromatography - mass spectrometry it was found that some of the basidiomycetes were able to remove both free and esterified sitosterol (75-100% degradation by Poria subvermispora Pilát, Phlebia radiata Fr., F. trogii, and Bjerkandera adusta (Willd.) P. Karsten), which has been identified as a major constituent of pitch deposits in eucalypt pulps, whereas the action of ascomycetes was mainly limited to hydrolysis of the sitosterol esters.