Nitrogenase activity of Beijerinckia derxii is preserved under adverse conditions for its growth

In order to evaluate the response of Beijerinckia derxii ICB-10 to different environmental factors, growth curves and specific nitrogenase activity were studied. Tested conditions were as follows: a) media with different pH values (2.5, 2.8, 4.2 and 5.7); b) medium supplemented with 230 æM aluminium sulphate; c) media with two different potassium phosphate concentrations (50 mM and 100 mM); d) shaken or still cultures; e) medium supplemented with 40 mM sodium thiosulphate. Growth curves and specific nitrogenase activity at pH 4.2 were closely similar to those for cultures at pH 5.7 (standard condition), whereas no growth occurred at pH 2.5. Changes in growth curves and/or specific nitrogenase activity were observed under the following conditions: I) pH 2.8 (decrease in initial CFU number, reduction of maximum specific growth rate, reduced number of generations and stimulation of nitrogenase activity), II) presence of aluminium (early death phase), III) 50 mM PO4(3-) (reduction of maximum specific growth rate), IV) 100 mM PO4(3-) (reduction of both number of generations and maximum specific growth rate as well as early death phase), V) low O2 availability (increasing nitrogenase activity), and VI) presence of thiosulphate (reduction of maximum specific growth rate; early death phase and high stimulation of nitrogenase activity). The data obtained showed the high variability of the cell growth response to environmental factors. Nitrogenase activity was always preserved even when population growth was affected

A study of the influence of pH and of dissolved oxygen concentration on BHK-21 cells growth

In a joint project of IPT (Instituto de Pesquisas Tecnológicas do Estado de São Paulo) and Vallée S.A., the growth of BHK-21 cells, used for the production of a vaccine against foot-and-mouth disease, was studied. The present work aimed the evaluation of the influence of and dissolved oxygen concentration on this growth. Assays were performed in a 2 L stirred bioreactor, with a BHK-21 cell line supplied by Vallée S.A. The culture medium contained glucose, several amino acids, vitamins and bovine serum. Seven experiments were performed, in which pH varied between 6.8 and 7.4, and the dissolved oxygen concentration between 2 and 60(per cent) of air saturation. The definition of optimal values was based on analysis of cell productivity and amounts of cells produced at the point at which the cultures attained maximal cell concentration. Optimal values for these paramenters were observed at pH 7.2 and 10 per cente dissolved oxygen concentration.