Heat and cold shock responses in different strains of Thiobacillus ferrooxidans

Gene expression modulation by heat stress in Acidithiobacillus ferrooxidans LR

During bioleaching, Acidithiobacillus ferrooxidans is subjected to different types of stress, including heat stress, which affect bacterial growth. In this work, real time quantitative PCR was used to analyze the expression of heat shock genes, as well as genes that encode proteins related to several functional categories in A. ferrooxidans. Cells were submitted to long-term growth and heat shock, both at 40°C. The results showed that heat shock affected the expression levels of most genes investigated, whilst long-term growth at 40°C resulted in minor changes in gene expression, except for certain genes related to iron transport, which were strongly down-regulated, suggesting that the iron processing capability of A. ferrooxidans was affected by long-term growth at 40°C. A bioinformatic analysis of the genes' promoter regions indicated a putative transcriptional regulation by the σ(32) factor in 12 of the 31 genes investigated, suggesting the involvement of other regulatory mechanisms in the response of A. ferrooxidans to heat stress.

Heat and phosphate starvation effects on the proteome, morphology and chemical composition of the biomining bacteria Acidithiobacillus ferrooxidans

Acidithiobacillus ferrooxidans is a Gram negative, acidophilic, chemolithoautotrophic bacterium that plays an important role in metal bioleaching. During bioleaching, the cells are subjected to changes in the growth temperature and nutrients starvation. The aim of this study was to gather information about the response of the A.ferrooxidans Brazilian strain LR to K2HPO4 starvation and heat stress through investigation of cellular morphology, chemical composition and differential proteome. The scanning electron microscopic results showed that under the tested stress conditions, A. ferrooxidans cells became elongated while the Fourier transform infrared spectroscopy (FT-IR) analysis showed alterations in the wavenumbers between 850 and 1,275 cm(-1), which are related to carbohydrates, phospholipids and phosphoproteins. These findings indicate that the bacterial cell surface is affected by the tested stress conditions. A proteomic analysis, using 2-DE and tandem mass spectrometry, enabled the identification of 44 differentially expressed protein spots, being 30 due to heat stress (40°C) and 14 due to K2HPO4 starvation. The identified proteins belonged to 11 different functional categories, including protein fate, energy metabolism and cellular processes. The upregulated proteins were mainly from protein fate and energy metabolism categories. The obtained results provide evidences that A. ferrooxidans LR responds to heat stress and K2HPO4 starvation by inducing alterations in cellular morphology and chemical composition of the cell surface. Also, the identification of several proteins involved in protein fate suggests that the bacteria cellular homesostasis was affected. In addition, the identification of proteins from different functional categories indicates that the A. ferrooxidans response to higher than optimal temperatures and phosphate starvation involves global changes in its physiology.

The resilience and versatility of acidophiles that contribute to the bio-assisted extraction of metals from mineral sulphides

In this paper, a brief outline is presented on acidic ferric ion oxidation of mineral sulphides for the extraction of metals in both stirred tank reactors for mineral concentrates and heaps for low-grade ores. The identities and capabilities of the relatively few acidophiles that assist the oxidative processes are summarized and their responses to selected extremes in their growth environments described. Individually, the organisms adapt to the presence of high concentrations of heavy metals and other elements in the bioleaching environment, tolerate a wide range of acidities and can recover from prolonged exposure to temperatures significantly above their preferred temperatures for growth. However, the presence of chloride in their acidic environment presents a significant physiological challenge. Species that exhibit a chemotactic response and attachment to sulphide surfaces, where they can create their own micro-environments, would be favoured in both heap bioreactors with low availability of energy substrates and physically aggressive, agitated continuous stirred-tank reactor environments treating concentrates.