THE ROLE OF THE PHOU PROTEIN IN SINORHIZOBIUM MELILOTI

Abstract

<p>Phosphate is of central importance in cellular metabolism and since bacteria are often exposed to various concentration of phosphorous in their environment, they have acquired various Pi transport systems for its uptake. <em>Sinorhizobium</em> <em>meliloti</em> has three Pi-uptake systems: a low affinity system encoded by <em>pap</em>-<em>pit</em> and two ABC type systems encoded by the <em>phnCDET</em> and <em>pstSCAB</em> operons. It is currently known that PstSCAB₂, a high affinity, high velocity transporter is induced under Pi limiting conditions and its transcription is controlled mainly in a PhoB-P dependent manner. During excess phosphate conditions, the negative regulation of the Pho regulon seems to involve PstSCAB₂ and PhoU. PhoU appears to be a negative regulator of the Pho regulon however; the mechanism by which PhoU accomplishes this task is currently unknown. In <em>Escherichia</em> <em>coli</em> and some other bacteria, mutations in <em>phoU</em> result in constitutive Pho regulon expression as do mutations in the <em>pstSCAB</em> genes. In order to address the function of PhoU in <em>Sinorhizobium</em> <em>meliloti</em>, we report the creation of a <em>Sinorhizobium</em> <em>meliloti</em> <em>ΔphoU</em> mutant strain. Results from the analysis of the <em>S. meliloti ΔphoU</em> strain suggest that this mutant behaves similarly to <em>E. coli phoU </em>mutant where one observes constitutive expression of the Pho regulon.</p>