Fertility promoting metabolites by Azotobacter vinelandii grown on olive mill wastewaters.

Olive-mill wastewaters OMW diluted to 5% organic matter (d.w.) were inoculated in a 2-1 bioreactor (T = 30°C, air flow = 1.41 min-1 stirring = 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 polysaccharides were determined after 2 weeks. Microbial growth, assayed as oxygen consumption, reached the steady state after 4 days. Auxin biosynthesis became evident as nitrogen fixation decreased. A two- to threefold increase in auxin production was recorded when tryptophan was added to OMW. Exo- and capsular polysaccharides were respectively present in amounts of 1 and 4 mg ml-1.