Effects of Escherichia coli Alkaline Phosphatase PhoA on the Mineralization of Dissolved Organic Phosphorus

Abstract

Alkaline phosphatases, which play the key role in the mineralization of organic phosphorus, have been grouped into three distinct families, PhoA, PhoX, and PhoD. PhoA is still an important component of the Pho regulon for many microbes although its distribution is not as wide as that of PhoX and PhoD. However, several questions remain unclear about the effect of PhoA mineralization of dissolved organic phosphorus. In this study, the role of Escherichia coli alkaline phosphatase PhoA (hereinafter referred to as PhoA) in the mineralization of different organic phosphorus including phosphate monoesters, phosphate diesters, and phytic acids was investigated. The influence of the reaction time, organic phosphorus concentration, and L-amino acid on PhoA mineralization was examined. The results show that PhoA specifically hydrolyzes phosphate monoesters except for phytic acid and the optimal reaction time is around 12 h. The PhoA mineralization rate of glucose 6-phosphate disodium (G6P), 5′-adenosine monophosphate (AMP), and sodium glycerophosphate (BGP) significantly decreased by 38.01%, 55.31%, and 57.08%, respectively (p < 0.01), while the concentration of organic phosphorus increased from 0.50 to 5.00 mg/L. Overall, L-amino acids inhibited PhoA mineralization in a concentration-independent manner. The inhibitory effect of neutral amino acids serine (L-Ser) and tyrosine (L-Tyr) was significantly higher than that of basic amino acids arginine (L-Arg), lysine (L-Lys), and histidine (L-His). All the five amino acids can inhibit PhoA mineralization of AMP, with the highest inhibition rate observed for L-Tyr (23.77%), the lowest—for L-Arg (1.54%). Compared with other L-amino acids, L-Tyr has the highest G6P and BGP mineralization inhibition rate, with the average inhibition rates of 12.89% and 11.65%, respectively. This study provides meaningful information to better understand PhoA mineralization.