Cloning, sequencing and characterization of a novel phosphatase gene, phoI, from soil bacterium Enterobacter sp. 4

Kinetic characterization of a novel acid ectophosphatase from Enterobacter asburiae

Expression of acid ectophosphatase by Enterobacter asburiae, isolated from Cattleya walkeriana (Orchidaceae) roots and identified by the 16S rRNA gene sequencing analysis, was strictly regulated by phosphorus ions, with its optimal activity being observed at an inorganic phosphate concentration of 7 mM. At the optimum pH 3.5, intact cells released p-nitrophenol at a rate of 350.76 ± 13.53 nmol of p-nitrophenolate (pNP)/min/10(8) cells. The membrane-bound enzyme was obtained by centrifugation at 100,000 × g for 1 h at 4 °C. p-Nitrophenylphosphate (pNPP) hydrolysis by the enzyme follows "Michaelis-Menten" kinetics with V = 61.2 U/mg and K0.5 = 60 μM, while ATP hydrolysis showed V = 19.7 U/mg, K0.5 = 110 μM, and nH = 1.6 and pyrophosphate hydrolysis showed V = 29.7 U/mg, K0.5 = 84 μM, and nH = 2.3. Arsenate and phosphate were competitive inhibitors with K i = 0.6 mM and K i = 1.8 mM, respectively. p-Nitrophenyl phosphatase (pNPPase) activity was inhibited by vanadate, while p-hydroxymercuribenzoate, EDTA, calcium, copper, and cobalt had no inhibitory effects. Magnesium ions were stimulatory (K0.5 = 2.2 mM and nH = 0.5). Production of an acid ectophosphatase can be a mechanism for the solubilization of mineral phosphates by microorganisms such as Enterobacter asburiae that are versatile in the solubilization of insoluble minerals, which, in turn, increases the availability of nutrients for plants, particularly in soils that are poor in phosphorus.

A Novel Phytase appA from Citrobacter amalonaticus CGMCC 1696: Gene Cloning and Overexpression in Pichia pastoris

A novel phytase gene appA, with upstream and downstream sequences from Citrobacter amalonaticus CGMCC 1696, was cloned by degenerate polymerase chain reaction (PCR), and thermal asymmetric interlaced (TAIL) PCR and was overexpressed in Pichia pastoris. Sequence analysis revealed one open reading frame that consisted of 1311 bp encoding a 436-amino-acid protein, which had a deduced molecular mass of 46.3 kDa. The phytase appA belongs to the histidine acid phosphatase family and exhibits the highest identity (70.1%) with C. braakii phytase. The gene was overexpressed in P. pastoris. The secretion yield of recombinant appA protein was accumulated to approximately 4.2 mg.mL(-1), and the enzyme activity level reached 15,000 U x mL(-1), which is higher than any previous reports. r-appA was glycosylated, as shown by Endo H treatment. r-appA was purified and characterized. The specific activity of r-appA for sodium phytate was 3548 U.mg(-1). The optimum pH and temperature for enzyme activity were 4.5 and 55 degrees C, respectively. r-appA was highly resistant to pepsin or trypsin treatment. This enzyme could be an economic and efficient alternative to the phytases currently used in the feed industry.