Abstract
A strain of a fungal species, i.e., Dichostereum sordulentum, not yet isolated from either Uruguay or decayed Eucalyptus spp. wood, was investigated for its ability of producing extracellular ligninolytic enzymes. To this aim, the strain was grown on a N-rich liquid medium added with either bark or wood Eucalyptus dunnii sawdust. The former additive was more effective than the latter instimulating laccase leading to a production of 4.78 IU mL-1 which was further enhanced by the concomitant presence of 80 ppm CuSO4 (6.56 IU mL-1). The two order of magnitude higher proanthocyanidin content in bark than in wood suggests that this fraction might be responsible for the higher stimulatory effect of the former on laccase production.
Highlights
In Uruguay, the forestry industry has grown in the last 20 years
Fruit bodies of the white rot fungus studied were identified as Dichostereum sordulentum (Cooke and Massee) Boidin and Lanquetin based on macro- and microcharacteristics of the basidiocarps based on descriptions of Boidin and Lanquetin (1980) [23]
The same tests for peroxidase were negative. These are semiquantitative tests, the high positive laccase reaction observed and the absence of information regarding the ligninolytic enzyme production by this species prompted us to perform further experiments in liquid cultures in the presence of sawdust derived from the same medium from which D. sordulentum had been isolated, namely E. dunnii wood and bark
Summary
Eucalyptus wood is used to produce cellulose pulp and significant amounts of bark are generated as byproducts. Eucalyptus bark composition is well known to be rich in extractives. Lipophilic fractions have been shown to contain triterpenic acids [2] and around twenty phenolic compounds were identified from methanolic extracts of different Eucalyptus species [3]. Lignin is efficiently decomposed by Basidiomycetes belonging to the ecological group of white-rot fungi. Due to the structural complexity of lignin and its random phenylpropanoic polymeric structure, enzymes involved in its degradation rely on radical-based reactions and exhibit a very low substrate specificity [4]. Three are the most important extracellular enzymes involved in this process, lignin peroxidases, manganese peroxidases and laccases. Laccases and Mnperoxidases are more widely distributed among white-rot fungi than lignin peroxidases [5]
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