Abstract:It is nearly always assumed that phosphorus (P) occurs exclusively as phosphate (with an oxidation state of +5) in the environment. Little is known about the redox cycle of P in the environment. However, recent evidence suggested that other less oxidized forms of P (namely reduced P, with an oxidation state lower than +5) that were more soluble and active play a critical role in P bioavailability. A bacterial strain (which was named P1) capable of utilizing phosphite (+3) as the sole P source was isolated and screened firstly from sediment of Lake Taihu. It was identified preliminarily as an unknown bacterium according to its physiological-biochemical analysis and the similarity analysis of its 16S rDNA gene sequence. The optimum conditions of pH and temperature for P1 growth were 6.8~7.0 and 30 oC, respectively. The concentrations of 60 mg P/L, 80 mg P/L and 100 mg P/L were set to obtain the optimum phosphite concentration for P1 growth. 100 mg P/L phosphite was the optimum P concentration for P1 growth, the rates of the decrease of phosphite and the increase of phosphate in the medium were 11% and 1.6%, respectively. The lower the phosphite concentration, the higher the activity of bacterial alkaline phosphatase (BAP) in the medium. The highest activity of BAP of 1.86 mol PNP/(L·h) was obtained under 60 mg P/L phosphite was added. Phosphite might be changed into the bioavailable P source for P1through the oxidation process of BAP. This study just simply found that phosphite can be utilized as a P source by a kind of bacteria. Further research should be carried out to investigate the role of phosphite in the lake P biogeochemical cycle.