OPTIMAL-GROWTH CONDITIONS FOR ACINETOBACTER ISOLATES FROM ACTIVATED-SLUDGE TREATING FOREST-INDUSTRY WASTEWATERS

Three Acinetobacter isolates (identified by API 20 NE as A. baumannii, A. junii, A. Iwoffii) from activated sludge treating forest-industry wastewaters were used as model organisms for polyphosphate-accumulatin g bacteria to optimize growth conditions for acinetobacters. The optim al concentrations of carbon, nitrogen, phosphorus, magnesium and potas sium for the growth of these isolates were determined by using four se ts of factorially designed experiments, Maximum growth was obtained wi th an average C:N:P ratio of 100:14:1.5 (on a weight basis) in the med ium. The average N:P ratio of about 10 is twice the ratio that is usua lly considered optimal for bacterial growth in activated sludge. Magne sium and potassium are crucial for polyphosphate metabolism. A. bauman nii did not respond to either magnesium or potassium additions, and A. junii had a linear response to potassium. Comparison of the optimal m olar Mg:P (0.93-1.8) and K:P (0.56) ratios obtained for A. Iwoffii and A. junii in the experiments to the corresponding ratios in the influe nt wastewaters indicates that magnesium and potassium would not limit growth and concomitant polyphosphate formation in acinetobacters. The results based on the optimal concentrations of elements in the medium may provide a better basis for optimizing the growth conditions than d ata on the chemical composition of bacterial cells.