SummaryWhite-rot fungi, which have the ability to degrade all the wood components including lignin, are of great interest in biotechnological processes based on wood and other lignocellulosic materials. It was demonstrated earlier that enough lignin can be degraded to cause a decrease in the energy demand for production of thermomechanical pulp if wood chips are pretreated by cellulaseless mutants of whiterot fungi. This paper concerns the growth conditions in wood for three white-rot fungi and their cellulaseless mutants in order to determine optimal conditions for such pretreatment processes. The pH and temperature optima have been determined as well as the growth rate in wood. The results show that the growth rate in wood, at least for Cel44 (a cellulaseless mutant of Sporotrichum pulverulentum), is not the rate-limiting step in delignification. From different mixtures of urea and NH,H,PO, the optimal nitrogen source was determined for the mutants. The optimal CIN ratio was found to vary between 16011 and 40011. It is suggested that the lower the CIN ratio, the faster the growth. It was also demonstrated that both water-and acetoneextractable substances in wood supported the growth of cellulaseless mutants. When some glucose was added to the wood, the weight loss caused by Cel 44 increased.All these observations support earlier findings that lignin in wood cannot be degraded by white-rot fungi unless a more easily metabolizable carbon source is used simultaneously.

Keywords Biodegradation Microscopy SEM White-rot f ungi Cellulase-less mutants Schlüsselwörter (Sachgebiete) Biologischer Abbau Mikroskopie REM Weißfäulepilze Cellulasefreie Mutanten A Scanning Electron Microscopy Study of the Growth and Attack on Wood by Three White-Rot Fungi and their Cellulase-less Mutants SummaryWhite-rot fungi, which have the ability to degrade all the wood components including lignin, are of great interest in biotechnological processes based on wood and other ligno-cellulosic materials. It was earlier demonstrated that enough lignin can be degraded to cause a decrease in the energy demand for the production of mechanical pulp if wood chips are pretreated by cellulase-less mutants of white-rot fungi. In view of these facts it has been important to study the growth pattern in wood of the wild-type (WT) white-rot fungi and their cellulase-less mutants. In this paper, the growth patterns of WT fungi and mutants, and the micro-morphological changes in wood emanating from attack by these different organisms, have been investigated by the aid of scanning electron microscopy (SEM). The results show that, although difTerences exist between WT fungi and mutants, the similarities are more striking. Probably the main difference between WT fungi and mutants is that the WT organisms can cause thinning of the wood cell walls whereas the mutants are unable to do so. It should also be pointed out that WT Sporotrichum pulverulentum causes bore holes in the wood fibre cell walls while its cellulase-less mutant, Cel 44, does not. Untersuchungen über Wachstum und Holzangriff von drei Weißfäulepilzen und deren cellulasefreien Mutanten mit Hilfe der Raster-Elektronenmikroskopie ZusammenfassungWeißfäulepilze, die die Fähigkeit besitzen, alle Holzbestandteile einschließlich Lignin abzubauen, sind für biotechnologische Prozesse, die sich auf Holz oder andere ligno-cellulosische Materialien beziehen, von großem Interesse. Es konnte in vorausgegangenen Arbeiten gezeigt werden, daß soviel Lignin abgebaut werden kann, daß der Energiebedarf bei der Holzstofferzeugung sinkt, wenn die Hackschnitzel mit cellulasefreien Mutanten des Weißfäulepilzes vorbehandelt werden. Im Hinblick auf diese Tatsachen erschien es wichtig zu sein, die Wachstumsmuster der Wildtype (WT) des Weißfäulepilzes und deren cellulasefreien Mutanten im Holz zu studieren. In vorliegender Arbeit werden die Wachstumsmuster des Weißfäulepilzes und der Mutanten sowie die mikromorphologischen Veränderungen im Holz, die von dem Angriff dieser verschiedenen Mikroorganismen herrühren, mit Hilfe der Rasterelektronenmikroskopie untersucht. Die Ergebnisse zeigen, daß, obgleich Unterschiede zwischen den WT-Pilzen und den Mutanten bestehen, die Ähnlichkeiten überwiegen. Offenbar ist der Hauptunterschied zwischen den WT-Pilzen und den Mutanten der, daß die WT-Organismen ein Dünnerwerden der Holzzellwände verursachen können, wozu die Mutanten nicht fähig sind. Es sei auch erwähnt, daß die WT von Sporotrichum pulverulentum Bohrlöcher in der Holzfaserzellwand hervorrufen ...