LIGN@J PEROXIDASE PRODUCTION 223

Grethlein (1991), and Linko and Haapala (1992b) has employed acetate buffer in submerged batch

cultures of P. chrysosporium, but again activities remained under 200 U dm+’ level.

Although Kirk er al. (1978) mentioned also aconitate as a possible buffer in P. chrysosporiwn

lignin degradation systems, trans-aconitate has been reported as a buffer for lignin peroxidase

production only recently (Farrell ef al., 1987; Fartell, 1987a; Hammel and Moen, 1991; Kern et

al., 1989b; Kern, 1990; Kirk et al., 1990, Ma er al., 1990). According to Kern (1990) the initial

pH of 5.1 decreased to about 4.7 during the first 3 days with the mutant strain SC 26 grown on

glycerol under nitrogen limitation. The pH was then adjusted to 5.3 with no further corrections.

Kern (1990) reported more than 2000 U dm’ in small scale agitated cultures, and Ma er aI. (1990)

950 U dni’ in shake cultures with polyurethane foam immobilized P. chrysosporium.

According to Kirk et al. (1990) lignin peroxidase inactivates rapidly at a pH of less than 3. It

appears that the buffer systems generally used are not optimal for large scale operations. However,

in large scale industrial production automatic pH-control should be preferable, as was used by

Janshekar and Fiechter (1988) with a 42-liter agitated free pellet culture.

Temperature

Kirk er al. (1978) reported 39” to 40°C as the optimum growth temperature for Phonerochnefe

chrysosporium strain ATCC 34541. However, to my knowledge there is no report on systematic

optimization of temperature for the production of lignin peroxidase. In their later studies Kirk and

coworkers have routinely used 39” or 40°C in the cultivation of P. chrysosporium strains ATCC

24725 and ATCC 34541, and its mutant strain SC 26 also for the lignin peroxidase production

(Faison and Kirk, 1985; Jgger et al., 1985; Kirk er al., 1986a,c). Willershausen ef al. (1987a,b)

used 40°C in the production of lignin peroxidase with silicon tubing attached P. chrysosporim.

Fiechter and coworkers (I-eisola er al., 1985a,b; Leisola and Fiechter, 1985b) chose 37°C both for

the growth and production phases in lignin peroxidase fermentations. This temperature has also

been used by Kuwahara and Asada (1989), Tonon and Odier (1988); Asther and coworkers (Asther

er al., 1987a,b; Asther et al., 1988b, Capdevila et al., 1990), and most of the own work. Ma er

al. (1990) used 38°C throughout.

In their early work with an isolated unidentified P. chrysosporium strain Gold er al. (1984), and

Renganathan and Gold (1986) first grew the mycelial inoculum at 38°C as a stationary culture,

followed by enzyme production in a shake culture at 28°C. This is in a good agreement with the

discovery of Hatakka and Uusi-Rauva (1983), who a year earlier had reported that P. chrysospo-

rium degrades poplar lignin better at 28°C than at 39°C. Surprisingly, these observations seemed

to have been forgotten for several years. The production of extracellular microbial enzymes is

often greater at a lower temperature than that optimal for growth (Davies, 1963). According to