Abstract
* Corresponding author. Mailing address: U.R.A. C.N.R.S. 1450 "Ecologie Microbienne du Sol," Université Lyon I, Bat. 741 bd. du 11 Novembre 1918, 69622 Villeurbanne Cedex, France. Phone: (33) 72 44 82 89. Fax: (33) 72 43 12 23. Electronic mail address: NORMAND{at}ECOSOL.UNIV_LYON1.FR .