Identification of a Gene Cluster for the Formation of Extracellular Polysaccharide Precursors in the Chemolithoautotroph Acidithiobacillus ferrooxidans

Abstract

A cluster of five genes, proposed to be involved in the formation of extracellular polysaccharide (EPS) precursors via the Leloir pathway, have been identified in the acidophilic autotroph Acidithiobacillus ferrooxidans. The order of the genes is luxA-galE-galK-pgm-galM, encoding a LuxA-like protein, UDP-glucose 4-epimerase, galactokinase, phosphoglucomutase, and galactose mutarotase, respectively. The gal cluster forms a single transcriptional unit and is therefore an operon. Two other putative genes of the Leloir pathway, galU, potentially encoding UDP-glucose pyrophosphorylase, and a gene designated galT-like, which may encode a galactose-1-phosphate uridylyltransferase-like activity, were found unlinked in the genome. Using semiquantitative reverse transcription-PCR, the genes of the gal operon were shown to be expressed more during growth in iron medium than in growth in sulfur medium. The functions of galE, pgm, galU, and the galT-like gene were validated by complementation of Escherichia coli mutants and by in vitro enzyme assays. The data suggest that A. ferrooxidans is capable of synthesizing the EPS precursors UDP-glucose and UDP-galactose. In addition, genes rfbA, -B, -C, and -D were identified in the genome of A. ferrooxidans, suggesting that it can also synthesize the EPS precursor dTDP-rhamnose. Since EPSs constitute the major bulk of biofilms, this study may provide an initial model for the metabolic pathways involved in biofilm formation in A. ferrooxidans and aid in understanding the role of biofilms in mineral leaching and the formation of acid mine drainage.Acidithiobacillus ferrooxidans is an acidophilic, chemolithotrophic, mesophilic, ␥-proteobacterium that thrives at pH 2 and functions as part of a consortium of microorganisms for the industrial recovery of metals such as copper and gold (13,25). In the environment, the microorganism is found in mine drainage, coal wastes, and other acidic sites, especially where pyrite (FeS 2 ) is available as an energy source. A. ferrooxidans can obtain its energy and electron requirements from the oxidation of various forms of reduced sulfur and ferrous iron. It can also fix nitrogen and carbon dioxide.The attachment and adherence of A. ferrooxidans to mineral surfaces and the subsequent formation of biofilms are prerequisites to mineral dissolution, both in industrial operations and in natural environments (27). Biofilm formation is accompanied by the production of extracellular polysaccharides (EPSs) (28). Whereas the role of biofilm formation by A. ferrooxidans in metal solubilization has been actively studied (8, 28), little is known regarding the underlying genetics, biochemistry, and regulation of EPS formation by this microorganism.Many organisms use UDP-glucose, UDP-galactose, and dTDP-rhamnose as precursors or building blocks of EPS biosynthesis (33). The galactosides UDP-glucose and UDP-galactose are synthesized from glucose-1-phosphate by two enzymes of the Leloir pathway, GalU (glucose 1-phosphate-pyrophosphorylase) and GalE (UDP-glucose 4-ep...

Metabolic diversity among main microorganisms inside an arsenic-rich ecosystem revealed by meta- and proteo-genomics

“…genoscope.cns.fr/agc/microscope/carnoulescope), this bin contains several genes, such as galE and pgm involved in capsular biosynthesis in At. ferrooxidans (Barreto et al, 2005), suggesting a role of this strain in the formation of a biofilm.…”

Porphyromonas gingivalis galEIs Involved in Lipopolysaccharide O-Antigen Synthesis and Biofilm Formation

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A Lux-like Quorum Sensing System in the Extreme Acidophile Acidithiobacillus ferrooxidans

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