Temporal dynamics of genes involved in metabolic pathways of C and N of L. ferriphilum, in the industrial bioleaching process of escondida mine, Chile

The structure of the microbial community inhabiting the copper bioleaching heap at Escondida mine has been systematically monitored since the operation was started up (2006), using biomolecular and microbiological analyses. Recent molecular analyses showed that L. ferriphilum was one of the most abundant organisms in the process during year 2012. In order to study the biological dynamics of carbon and nitrogen in the process, the expression levels of thirteen genes of L. ferriphilum were analyzed by RT-qPCR. The 16S rRNA and alaS genes were used as reference, and two relative quantification methods (ΔΔct and and Pffafl) were applied to estimate the relative expression levels of metabolic genes. On the day 110 of operation, a significant increment in the expression level of one gene involved in the cycle of tricarboxilic acids (2-oxoglutarate-acceptor oxidoreductase, oorA) was detected. By other hand, the expression level of two genes involved in carbohydrate metabolism (glgP, Glycogen phosphorilase, and glgA, Glycogen synthase) gradually increased, as the operation time progressed. The expression levels of genes involved in the fixation and assimilation of nitrogen increased at later stages of the process. A significant increase of the expression level of the gene annotated for Nitrogenase iron protein (nifH) was detected on the day 185 of operation. The opposite trend was observed for the gene annotated as Ammonium transporter protein (amt), as an elevated expression level was observed in earlier stages to suddenly decrease on the day 185 of operation, suggesting a change of the nitrogen source. In agreement with molecular quantitative analyses, this work confirmed that L. ferriphilum was an active member of the community during the period studied. This work gives new insights into biological dynamics of carbon and nitrogen, and suggests the potential guidelines to enhance the efficiency of biological components in industrial heap bioleaching processes.