ORIGINAL PAPER M. M. Berrocal á J. RodrõÂguez á A. S. Ball M. I. PeÂrez-Leblic á M. E. Arias Solubilisation and mineralisation of [ 14 C]lignocellulose from wheat straw by Streptomyces cyaneus CECT 3335 during growth in solid-state fermentation Received: 12 May 1997 / Accepted: 19 May 1997 Abstract Nine Streptomyces strains were screened for their ability to solubilise and mineralise 14 C-labelled lignin during growth in solid-state fermentation. Strep- tomyces viridosporus was con®rmed as an active lignin- degrading organism along with a new isolate, Strepto- myces sp. UAH 15, further classi®ed as Streptomyces cyaneus CECT 3335. This organism was able to solubilise and mineralise the [ 14 C]lignin fraction of lignocellulose (44.96  1.77% and 3.41  0.48% respectively) after 21 days of incubation. Cell-free ®ltrates from Strepto- myces sp. grown in solid-state fermentation were capable of solubilising up to 20% of the [ 14 C]lignin after 2 days incubation, with most of the product detected in the acid- soluble rather than in the water-soluble fraction. Iden- ti®cation of the extracellular enzymes produced during growth of S. cyaneus CECT 3335 revealed that extracel- lular peroxidase and phenol oxidase activities were present, with the activity of phenol oxidase being 100 times greater than peroxidase activity. The activity of these two enzymes was found to correlate with both solubilisation and mineralisation rates. This is the ®rst report of phenol oxidase activity produced by a Strep- tomyces strain during growth in solid-state fermentation. A role for the enzyme in the solubilisation and miner- alisation of lignocellulose by S. cyaneus is suggested. Introduction There is evidence that lignin-solubilising actinomycetes can oxidatively depolymerise lignin while degrading the cellulose and hemicellulose components of plant mate- rial (Crawford 1986). The lignin substrate is primarily solubilised in the growth medium, in the form of lignin- derived monomers (Crawford 1981) and a substantially degraded acid-precipitable polymeric lignin (APPL) Crawford et al. 1983). Studies on novel oxidative enzymes involved in the attack of the lignin component were also initiated, and clari®cation of the relationship between lignin solubili- sation and degradation achieved (McCarthy and Ball 1991). The role of extracellular phenol oxidases (laccases) in lignin degradation by fungi has been suggested and it has recently been demonstrated that laccase can take part in lignin degradation (Bourbonnais and Paice 1990, 1992; Srinivasan et al. 1995). Although some speci®c phenol oxidases (tyrosinases) have been described in Streptomyces (Yoshimoto et al. 1985), at present phenol oxidases, possibly involved in the polymerisation of lignin fragments, have only been reported in Strepto- myces badius during growth in submerged culture (Borgmeyer and Crawford 1985). One possible biotechnological role for the lignin-de- grading organisms lies in the area of lignocellulose bio- conversion by solid-state fermentation. Progress in this area has been made with white-rot fungi (Rios and Ey- zaguirre 1992; Lobos et al. 1994; Valmaseda et al. 1994) and a recent report shows the production of oxidative enzymes in solid-state fermentation that have not pre- viously been described in liquid cultures (Vares et al. 1995). In previous studies in our laboratory, a phenol oxi- dase has been detected in cultures of Streptomyces sp. UAH 15, following growth in solid-state fermentation (Berrocal et al. 1996b). In this study, the same strain, classi®ed as Streptomyces cyaneus CECT 3335, was se- lected on the basis of a signi®cant yield of 14 CO 2 from [ 14 C]lignin and the ability to solubilise lignocellulose. This strain was grown under solid-substrate fermenta- tion conditions using wheat straw as substrate. The supernatants from cultures with maximum values for Appl Microbiol Biotechnol (1997) 48: 379±384 Ó Springer-Verlag 1997 M. M. Berrocal á J. RodrõÂguez á M. I. PeÂrez-Leblic M. E. Arias (&) Departamento de MicrobiologõÂa y ParasitologõÂa, Universidad de AlcalaÂ, 28871 Alcala de Henares, Madrid, Spain Tel.: (91) 8854633 Fax: (91) 8854623 e-mail: MPMAF@ALCALA.ES A. S. Ball Department of Biological and Chemical Sciences, University of Essex, Wivenhoe Park, Colchester, C043SQ, UK