Optimal growth conditions for Acinetobacter isolates from activated sludge treating forest-industry wastewaters

Abstract

Three Acinetobacter isolates (identified by API 20 NE as A. baumannii, A. junii, A. lwoffii) from activated sludge treating forest-industry wastewaters were used as model organisms for polyphosphate-accumulating bacteria to optimize growth conditions for acinetobacters. The optimal concentrations of carbon, nitrogen, phosphorus, magnesium and potassium for the growth of these isolates were determined by using four sets of factorially designed experiments. Maximum growth was obtained with an average C:N:P ratio of 100:14:1.5 (on a weight basis) in the medium. The average N:P ratio of about 10 is twice the ratio that is usually considered optimal for bacterial growth in activated sludge. Magnesium and potassium are crucial for polyphosphate metabolism. A. baumannii did not respond to either magnesium or potassium additions, and A. junii had a linear response to potassium. Comparison of the optimal molar Mg:P (0.93–1.8) and K:P (0.56) ratios obtained for A. lwoffii and A. junii in the experiments to the corresponding ratios in the influent 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 data on the chemical composition of bacterial cells.