Phosphate uptake and release by Acinetobacter johnsonii in continuous culture and coupling of phosphate release to heavy metal accumulation

A strain of polyphosphate-synthesizing, phosphate-releasing Acinetobacter j ohnsonii was isolated from a wastewater treatment plant operating enhanced biological phosphate removal (EBPR) and was used to remove La3+ from soluti on via precipitation of cell-bound LaPO4. The effect of repeated aerobic-an aerobic cycles on the carbon and phosphate metabolism of the organism was s tudied in attempts to promote increased phosphate flux using a three-stage, continuous bioreactor comprising aerobic, anaerobic and settling vessels. The bioreactor was operated in two modes: In flow-through mode, cells were grown aerobically with acetate as the sole carbon source, promoting excess phosphate uptake (up to 5.0 mmol/l=3.0 mmol/g protein). Cells were diluted into the anaerobic vessel where phosphate was released (up to 1.0 mmol/l=0. 3 mmol/g protein), and thence to waste. The system was initially operated t o steady state in flow-through mode, then switched to recycle mode. Here th e anaerobic vessel output passed to a settling vessel from which settled ce lls were returned to the aerobic vessel. Carbon source (acetate) was suppli ed only to the anaerobic vessel; increased anaerobic acetate uptake was obs erved during recycle, which was sustained when the system was returned to f low-through mode and was related to increased cellular lipid inclusions by flow cytometry and electron microscopy. These phenomena may represent adapt ation of cells to aerobic-anaerobic cycling with aerobic carbon/energy limi tation. Addition of La3+ to the anaerobic vessel during recycle mode promot ed removal of 95% of the La3+ from a 0.1 to 0.3 mM (14-42 ppm) solution at the expense of biogenic phosphate.