K-103. Metabolic and Regulatory Networks in Extreme Acidophiles: Gaining Energy from Rocks at pH 2

J. Valdes1, R. Quatrini1, E. Jedlicki2, I. Pedroso1, D. S. Holmes1;
1Ctr. for Bioinformatics and Genome Biology, Life Science Fndn, MIFAB and Andrés Bello Univ., Santiago, CHILE, 2ICBM, Faculty of Med., Univ. of Chile, Santiago, CHILE.

Background: Acidithiobacillus ferrooxidans, A. thiooxidans and A. caldus are chemolithoautotrophic γ-proteobacteria that thrive at pH2 and derive energy from the oxidation of iron and sulfur. They fix CO2 and nitrogen. They are important in industrial bioleaching operations for the recovery of copper and gold and play important roles in the biogeochemical cycling of metals and nutrients in naturally acidic environments. We have annotated their genomes and have carried out comparative genomics in order to shed light on their metabolism and genetic regulatory circuits. Bioinformatic and genomic approaches to unraveling their biology are particularly valuable given the low growth rates and yields of these microorganisms and difficulties encountered in their genetic manipulation. Methods: Draft genome sequences were generated from A. thiooxidans and A. caldus and were assembled, annotated and compared to the publicly available genome sequence of A. ferrooxidan. Results: The presence or absence of predicted genes is reported for eleven metabolic and phenotypic characteristics of the three acidithiobacilli: CO2 fixation, TCA cycle, sulfur oxidation, sulfur reduction, iron oxidation, iron assimilation, quorum sensing, hydrogen oxidation, flagella formation, chemotaxis and nitrogen fixation. Predicted transcriptional and metabolic interplay between pathways pinpoints potential coordinated responses to environmental signals such as energy source and nutrient limitations. Conclusion: This study provides preliminary metabolic and regulatory models for each species and predicts important interactions that may occur between them in the environment (ecophysiology). Several responses appear to be especially characteristic of autotrophic microorganisms and may have direct implications for metabolic processes of critical relevance to understanding how these microorganisms survive and proliferate in extreme environments.