Effects of extracts of Alnus glutinosa seeds on growth of Frankia strain ArI3 under static and fermentor culture conditions

In the present study, the effect of Alnus glutinosa seed extract on the in vitro growth of Frankia strain ArI3 was investigated under various culture conditions. Frankia filaments grown in static cultures showed a very slow growth with doubling time of 12 days. However, under the same growth conditions but with seed extract added to the medium, the doubling time was reduced to 6 days. A further reduction in doubling time (2.5 days) was obtained without seed extract when Frankia strain ArI3 was grown in a fermentor with continuous stirring. Under these culture conditions, seed extract did not influence the Frankia growth rate. In all our studies, Na-propionate was used as the only carbon source. Gradual addition of Na-propionate to Frankia cultures in the fermentor sustained exponential growth of the filaments over a prolonged period. The complete consumption of Na-propionate was the limiting growth factor under fermentor growth conditions. The mechanism of growth stimulation by Alnus glutinosa seed extract under growth limiting conditions in static cultures and its possible ecological significance is discussed.