Bis-(3′–5′)-cyclic dimeric guanosine monophosphate (c-di-GMP) is an important intracellular signaling molecule that affects diverse physiological processes in bacteria. The intracellular levels of c-di-GMP are controlled by proteins acting as diguanylate cyclase (DGC) and phosphodiesterase (PDE) enzymes that synthesize and degrade c-di-GMP, respectively. In the alphaproteobacterium Rhodobacter capsulatus, flagellar motility and gene exchange via production of the gene transfer agent RcGTA are regulated by c-di-GMP. One of the R. capsulatus proteins involved in this regulation is Rcc00620, which contains an N-terminal two-component system response regulator receiver (REC) domain and C-terminal DGC and PDE domains. We demonstrate that the enzymatic activity of Rcc00620 is regulated through the phosphorylation status of its REC domain, which is controlled by a cognate histidine kinase protein, Rcc00621. In this system, the phosphorylated form of Rcc00620 is active as a PDE enzyme and stimulates gene transfer and motility. In addition, we discovered that the rcc00620 and rcc00621 genes are present in only one lineage within the genus Rhodobacter and were acquired via horizontal gene transfer from a distantly related alphaproteobacterium in the order Sphingomonadales. Therefore, a horizontally acquired regulatory system regulates gene transfer in the recipient organism.

双（3'-5'）-环二聚鸟苷单磷酸鸟苷（c-di-GMP）是一种重要的细胞内信号分子，可影响细菌的多种生理过程。c-di-GMP的细胞内水平由分别充当合成和降解c-di-GMP的双鸟苷酸环化酶（DGC）和磷酸二酯酶（PDE）的蛋白质控制。在荚膜红杆菌中，鞭毛运动和通过产生基因转移剂RcGTA的基因交换受c-di-GMP调控。其中的R.荚膜参与该调控的蛋白质是Rcc00620，它包含一个N端两组分系统响应调节剂受体（REC）域和C端DGC和PDE域。我们证明Rcc00620的酶活性是通过其REC域的磷酸化状态来调节的，该状态由相关的组氨酸激酶蛋白Rcc00621控制。在该系统中，Rcc00620的磷酸化形式作为PDE酶具有活性，并刺激基因转移和运动。此外，我们发现rcc00620和rcc00621基因仅存在于红细菌属中的一个谱系中并通过水平基因转移从远缘的α变形杆菌中以Sphingomonadales顺序获得。因此，水平获得的调节系统调节受体生物体中的基因转移。