Abstract

Leptospirillum ferriphilum has been determined as one of the most abundant iron oxidizer species in the microbial communities of two industrial copper bioleaching processes, in northern Chile [1,2]. A common threat faced by microbial communities inhabiting this type of environments is the loss of internal water, arising from elevated concentrations of dissolved solutes producing a decrease of water activity in the solutions of the industrial circuits. In spite of the importance of bioleaching microorganisms, few studies have been focused on determining the mechanisms and molecules (osmo-protectants) involved in their water homeostasis. In order to identify the osmo-protectants in L. ferriphilum, three strains including L. ferriphilum DSM 14647 (type strain), L. ferriphilum IESL25 (isolated from Escondida mine) and L. ferriphilum Sp-Cl (isolated from Spence mine) were cultured in the presence of increasing concentrations of magnesium sulfate. Chromatographic analyses revealed the presence of trehalose as an important osmo-protectant when cultures were grown at elevated osmotic strength. The trehalose produced by these strains increased approximately from 18 to 26 times in cultures amended with 300 mM of magnesium sulfate, compared to non amended cultures. Genomic information has suggested the potentiality of L. ferriphilum to synthesize several osmoprotectants in response to osmotic stress, however the amount of trehalose produced by the strains studied in this work represented between 18 and 24% of total wet weight, suggesting this dissacharide as one of the most important osmo-protectant in this species. In addition, comparative proteomic analyses performed in cultures of L. ferriphilum IESL25 showed differential expression of proteins related to stress (GroEL and sHSp20) and carbohydrates metabolism (Isocitrate dehydrogenase and succinyl CoA synthetase). Although, proteins directly related to the synthesis of trehalose were not detected by differential proteomic analysis, the results suggests changes in the dynamics of Citric acid cycle pathway (TCA) in response to elevated osmotic strength by L. ferriphilum. This work identifies trehalose as an important osmoprotectant in L. ferriphilum and highlights the importance of carbon availability in industrial bioleaching processes operating at elevated osmotic strength.