Rivas Mariella, Seeger Michael, Jedlicki Eugenia, Holmes David S
Institute of Cellular and Molecular Biology, Faculty of Medicine, University of Chile, Santiago, Chile.
Appl Environ Microbiol. 2007 May;73(10):3225-31. doi: 10.1128/AEM.02948-06. Epub 2007 Mar 9.
The acidophilic proteobacterium Acidithiobacillus ferrooxidans is involved in the industrial biorecovery of copper. It is found in acidic environments in biofilms and is important in the biogeochemical cycling of metals and nutrients. Its genome contains a cluster of four genes, glyQ, glysS, gph, and act, that are predicted to encode the alpha and beta subunits of glycine tRNA synthetase, a phosphatase, and an acyltransferase, respectively (GenBank accession no. DQ149607). act, cloned and expressed in Escherichia coli, produces acyl homoserine lactones (AHLs) principally of chain length C14 according to gas chromatography and mass spectrometry measurements. The AHLs have biological activity as shown by in vivo studies using the reporter strain Sinorhizobium meliloti Rm41 SinI-. Reverse transcription-PCR (RT-PCR) experiments indicate that the four genes are expressed as a single transcript, demonstrating that they constitute an operon. According to semiquantitative RT-PCR results, act is expressed more highly when A. ferrooxidans is grown in medium containing iron than when it is grown in medium containing sulfur. Since AHLs are important intercellular signaling molecules used by many bacteria to monitor their population density in quorum-sensing control of gene expression, this result suggests that A. ferrooxidans has two quorum-sensing systems, one based on Act, as described herein, and the other based on a Lux-like quorum-sensing system, reported previously. The latter system was shown to be upregulated in A. ferrooxidans grown in sulfur medium, suggesting that the two quorum-sensing systems respond to different environmental signals that may be related to their abilities to colonize and use different solid sulfur- and iron-containing minerals.
嗜酸氧化亚铁硫杆菌这种嗜酸变形菌参与了铜的工业生物回收过程。它存在于酸性环境中的生物膜里，在金属和养分的生物地球化学循环中起着重要作用。其基因组包含一组四个基因，即glyQ、glysS、gph和act，预计分别编码甘氨酸tRNA合成酶的α和β亚基、一种磷酸酶和一种酰基转移酶（GenBank登录号：DQ149607）。根据气相色谱和质谱测量结果，在大肠杆菌中克隆并表达的act主要产生链长为C14的酰基高丝氨酸内酯（AHLs）。使用报告菌株苜蓿中华根瘤菌Rm41 SinI-进行的体内研究表明，这些AHLs具有生物活性。逆转录PCR（RT-PCR）实验表明这四个基因作为一个单一转录本表达，证明它们构成一个操纵子。根据半定量RT-PCR结果，嗜酸氧化亚铁硫杆菌在含铁培养基中生长时，act的表达比在含硫培养基中生长时更高。由于AHLs是许多细菌用于在群体感应基因表达控制中监测其群体密度的重要细胞间信号分子，这一结果表明嗜酸氧化亚铁硫杆菌有两个群体感应系统，一个基于本文所述的Act，另一个基于先前报道的类似Lux的群体感应系统。后一个系统在嗜酸氧化亚铁硫杆菌在硫培养基中生长时被上调，这表明这两个群体感应系统对不同的环境信号做出反应，这些信号可能与其定殖和利用不同的含硫和含铁固体矿物的能力有关。
