The effect of aeration level and iron concentration on Azotobacter chroococcum 23 growth, PHB accumulation and antioxidative enzyme activities was investigated in shake flask experiments. Biomass yield and carbon source conversation coefficients increased in the presence of iron in the growth medium and under decreased aeration. The highest biomass production was observed for the culture grown in a medium with 36 mu M of initial iron concentration and moderate aeration level. The highest PHB accumulation level (70-72% from cell dry weight) under our experimental conditions was observed at decreased aeration in the growth medium with 180 mu M of initial iron concentration. Results obtained prove that both aeration level and iron supply have a marked influence on the activity of SOD and catalase. Bearing in mind the necessity of iron for the synthesis of both enzymes, only catalase showed a specific dependence on the intracellular iron accumulation level. (C) 2008 Elsevier Ltd. All rights reserved.