Membrane-bound pyrophosphatase of human gut microbe <i>Clostridium methylpentosum</i> confers improved salt tolerance in <i>Escherichia coli</i>, <i>Saccharomyces cerevisiae</i> and tobacco

<p>Membrane-bound pyrophosphatases (PPases) are involved in the adaption of organisms to stress conditions, which was substantiated by numerous plant transgenic studies with H<sup>+</sup>-PPase yet devoid of any correlated evidences for other two subfamilies, Na<sup>+</sup>-PPase and Na<sup>+</sup>,H<sup>+</sup>-PPase. Herein, we demonstrate the gene cloning and functional evaluation of the membrane-bound PPase (CmPP) of the human gut microbe <i>Clostridium methylpentosum</i>. The <i>CmPP</i> gene encodes a single polypeptide of 699 amino acids that was predicted as a multi-spanning membrane and K<sup>+</sup>-dependent Na<sup>+</sup>,H<sup>+</sup>-PPase. Heterologous expression of CmPP could significantly enhance the salt tolerance of both <i>Escherichia coli</i> and <i>Saccharomyces cerevisiae</i>, and this effect in yeast could be fortified by N-terminal addition of a vacuole-targeting signal peptide from the H<sup>+</sup>-PPase of <i>Trypanosoma cruzi</i>. Furthermore, introduction of <i>CmPP</i> could remarkably improve the salt tolerance of tobacco, implying its potential use in constructing salt-resistant transgenic crops. Consequently, the possible mechanisms of CmPP to underlie salt tolerance are discussed.</p>