The effect of heavy metals and other environmental conditions on the anaerobic phosphate metabolism of Acinetobacter johnsonii

A strain of Acinetobacter with potential for bioremediation of heavy metal-contaminated waters was isolated from a wastewater-treatment plant operating an enhanced biological phosphate removal process. NMR and extractive methods showed that polyphosphate accumulated aerobically was degraded under anaerobic conditions both in the presence and absence of cadmium or uranium (0·2–0·5 mM). NMR showed that free phosphate was formed at the expense of polyphosphate, and an extractive technique indicated that this reaction could be stimulated by the presence of UO2 2+ under these conditions. Energy-dispersive X-ray microanalysis demonstrated that only cadmium could enter the cells, and co-localized with intra-cellular granules containing phosphate and other divalent metals. The effects of other environmental parameters on the anaerobic phosphate metabolism were also investigated. Between pH 5·5 and 8·0, phosphate release increased with increasing pH. Between 4°C and 37°C, phosphate release increased with increasing temperature. The presence of nitrate at concentrations of 10 mM and above inhibited anoxic phosphate release, but supplying tungstate in the growth medium prior to anoxic incubation reduced the production of active nitrate reductase and alleviated this effect.