PRINCIPLE OF A FRACTIONAL FACTORIAL DESIGN FOR QUALITATIVE AND QUANTITATIVE FACTORS APPLICATION TO THE PRODUCTION OF BRADYRHIZOBIUM-JAPONICUM IN CULTURE AND INOCULATION MEDIA

To improve the production of Bradyrhizobium japonicum in liquid cultur e media, different carbon and nitrogen substrates at different concent rations were tested. In order to study simultaneously these qualitativ e and quantitative factors, a suitable experimental design was necessa ry. We develop here the principle leading to such fractional factorial designs. The specific design used allowed us to decrease the theoreti cal number of treatments from 1 024 to 128 and to get estimates of fac torial main effects and 2-factor interactions. Five of the 7 tested fa ctors, pH, carbon and organic nitrogen sources, yeast extract concentr ation and organic nitrogen concentration, were found to have a signifi cant effect on optical density. They also were found to interact with each other. The design allowed us to select 2 media that produced more than 10(10) bacteria/ml.