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Appl. Environ. Microbiol. doi:10.1128/AEM.02101-07
Copyright (c) 2008, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

The chemolithoautotroph Acidithiobacillus ferrooxidans can survive under phosphate limiting conditions by the expression of a C-P lyase operon that allows it to grow on phosphonates

Laboratory of Molecular Microbiology and Biotechnology, Department of Biology, and Millennium Institute for Cell Dynamics and Biotechnology, Faculty of Sciences, University of Chile, Santiago, Chile

^* To whom correspondence should be addressed. Email: cjerez{at}uchile.cl.

	Abstract

The chemolithoautotrophic bacterium Acidithiobacillus ferrooxidans is of great importance in biomining operations. During bioleaching of ores microorganisms are subjected to a variety of environmental stresses and limitations of some nutrients such as inorganic phosphate (Pi), which is an essential component for all living cells. Although the primary source of phosphorus for microorganisms is Pi, some bacteria are also able to metabolize Pi esters (with a C-O-P bond) and phosphonates (with a very inert C-P bond). By using bioinformatic analysis of genomic sequences of the type strain of A. ferrooxidans (ATCC 23270) we found that as part of a Pho regulon, this bacterium has a complete gene cluster encoding for C-P lyase, which is the main bacterial enzyme involved in phosphonate (Pn) degradation in other microorganisms. A. ferrooxidans was able to grow in the presence of methyl-Pn or ethyl-Pn as alternative phosphorus sources. Under these growth conditions, a great reduction in inorganic polyphosphate (polyP) levels was seen when compared with cells grown in the presence of Pi. By means of RT-PCR, DNA macroarrays and real time RT-PCR experiments, it was found that A. ferrooxidans phn genes were co-transcribed, and their expression was induced when the microorganism was grown in methyl-Pn as the only phosphorus source. This is the first report of phosphonate utilization in a chemolithoautotrophic microorganism. The existence of a functional C-P lyase system is a clear advantage for the survival under Pi limitation, a condition that may greatly affect bioleaching of ores.