NEW APPROACH FOR SELECTING PECTINASE PRODUCING MUTANTS OF ASPERGILLUS-NIGER WELL ADAPTED TO SOLID-STATE FERMENTATION

The aim of this paper is to review and study a new approach for improv ing strains of Aspergillus niger specially adapted to produce pectinas es by Solid State Fermentation (SSF) with materials having low levels of water activity (a(w)), i.e., coffee pulp. Special emphasis is place d on the use of two antimetabolic compounds: 2-deoxy-glucose (DG) and 2,4-dinitro-phenol (DNP) combined with a water depressant (ethylene gl ycol = EG) in order to put strong selection pressures on UV treated sp ores from parental strain C28B25 isolated from a coffee plantation. Su ch a strain was found to be DG sensitive. Results suggested the existe nce of a reciprocal relation between adaptation of isolated strains to SSF or to Submerged Fermentation (SmF) systems. Preliminary physiolog ical analysis of isolated strains showed that at least some few initia lly DG resistant mutants could revert to DG sensitive phenotype but co nserving increased pectinase production. Also it was found that phenot ype for DNP resistance could be associated to changes of DG resistance . Finally, it was found that low levels of a(w) produced by adding 15% EG to agar plates, were a significant selection factor for strains we ll adapted to SSF system.