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.
Highlights
Being the first and well-studied alkaline phosphatase, E. coli PhoA is highly specific for the monophosphate ester bond but does not show specificity for the organic part and is able to hydrolyze a wide range of compounds [19]
Our results showed that PhoA could not mineralize Ribonucleic acid from baker’s yeast (RNA) and IP6-Na in the organic phosphorus solution with pH 8.00
The results showed that each L-amino acid inhibited PhoA mineralization in a conThe strongest inhibitory effect of L-Tyr on PhoA mineralization was observed in adenosine monophosphate (AMP)
Summary
The growth of phytoplankton is limited by nutrients such as nitrogen and phosphorus [1]. The role of phosphorus limitation in the primary productivity of eutrophic lakes has received extensive attention since 1970s [2,3,4]. When the most readily available dissolved inorganic phosphorus (Pi ) is in short supply, microorganisms satisfy the demand of phosphorus for growth and reproduction by releasing alkaline phosphatases (APases) to mineralize organic phosphorus [5]. At least three distinct prokaryotic alkaline phosphatases (PhoA, PhoX, and PhoD) have been identified based on their sequence similarities and substrate specificity [6]. PhoA, initially discovered to be expressed and synthesized by Escherichia coli [7], was the first alkaline phosphatase to be characterized [8]
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