Fertility-promoting metabolites produced 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.