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Appl. Environ. Microbiol. doi:10.1128/AEM.02948-06
Copyright (c) 2007, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

A second acyl homoserine lactone (AHL) producing system in the extreme acidophile, Acidithiobacillus ferrooxidans

Institute of Cellular and Molecular Biology (ICBM), Faculty of Medicine, University of Chile, Santiago, Chile, Laboratorio de Microbiolgía Molecular y Biotecnología Ambiental, Departamento de Química, Universidad Técnica Federico Santa María and Millennium Nucleus of Microbial Ecology and Environmental Microbiology and Biotechnology, Valparaíso, Chile and Center for Bioinformatics and Genome Biology, MIFAB, Life Science Foundation and Andrés Bello University, Santiago, Chile

^* To whom correspondence should be addressed. Email: dsholmes2000{at}yahoo.com.

	Abstract

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, gph1 and act1 that are predicted to encode the and subunits of glycine tRNA synthetase, a phosphatase and an acyltransferase, respectively (Genbank acc. DQ149607). Act1, cloned and expressed in E. 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^-. RT-PCR experiments indicate that the four genes are expressed as a single transcript demonstrating that they constitute an operon. According to semi-quantitative RT-PCR, act1 is expressed more when A. ferrooxidans is grown in medium containing iron versus one 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, it suggests that A. ferrooxidans has two quorum sensing systems, one based on Act1, as described herein, and the other on a Lux-like quorum sensing system, reported previously. The latter system was shown to be up regulated 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 ability to colonize and use different solid sulfur- and iron-containing minerals.

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