Screening for Lignin Degradation by White Rot Fungi

Lignin-degrading ability is commonly evaluated by measuring 14CO2 evolution from 14C-labeled lignin preparations, such as 14C-ring-labeled dehydrogenation polymerizate (DHP). The measurement of 14CO2 evolution is the most sensitive and accurate method for testing ligninolytic activity (Eriksson et al. 1990). The evolution of 14CO2 and the modification of DHP has been employed for determining ligninolytic activity in many white rot fungi as well as for elucidating the role of different enzymes and other constituents in lignin degradation (Boyle et al. 1992; CostaFerreira et al. 1996; Eggert et al. 1997; Hatakka 1994; Hatakka and Uusi-Rauva 1983; Hatakka et al. 1983; Hofrichter et al. 1999; Perez and Jeffries 1992; Reid and Deschamps 1991; Sethuraman et al. 1999; Silva et al. 1996; Umezawa and Higuchi 1989; Yoshida et al. 1998). Methods to study the degradation of polymeric lignin such as nuclear magnetic resonance spectroscopy have been developed (Davis et al. 1994; Gamble et al. 1994), but they are not easily amenable for detailed physiological studies with microorganisms or biochemical studies with enzymes.

A simple and reliable screening procedure that distinguishes between fungi that cause decay by selectively removing lignin and those that degrade both cellulose and lignin simultaneously has been developed involving staining of lignin with astra-blue, which stains cellulose blue only in the absence of lignin, and safranin, which stains lignin regardless of whether cellulose is present (Srebotnik and Messner 1994).

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