FERTILITY-PROMOTING METABOLITES PRODUCED BY AZOTOBACTER-VINELANDII GROWN ON OLIVE-MILL WASTEWATERS

Olive-mill wastewaters OMW diluted to 5% organic matter (d.w.) were in oculated in a 2-1 bioreactor (T=30 degrees C, air flow=1.41 min(-1) st ir ring=100 rpm) with a strain of Azotobacter vinelandii isolated from soils heavily treated with OMW. Microbial growth and auxin production were followed during the first week. Exo- and capsular polysaccharide s were determined after 2 weeks. Microbial growth, assayed as oxygen c onsumption, reached the steady state after 4 days. Auxin biosynthesis became evident as nitrogen fixation decreased. A two- to threefold inc rease in auxin production was recorded when tryptophan was added to OM W. Exo- and capsular polysaccharides were respectively present in amou nts of 1 and 4 mg ml(-1). (C) 1997 Published by Elsevier Science Limit ed.