Differential gene expression and bioinformatics analysis of copper resistance gene afe_1073 in Acidithiobacillus ferrooxidans

Metallurgical processes unveil the unexplored "sleeping mines" e- waste: a review

The aim of this review paper is to critically analyze the existing studies on waste electric and electronic equipment (WEEE), which is one of the most increasing solid waste streams. This complex solid waste stream has pushed many scientific communities to develop novel technologies with minimum ecological disturbance. Noteworthy amount of valuable metals makes e-waste to a core of "urban mining"; therefore, it warrants special attention. Present study is focused on all the basic conceptual knowledge of WEEE ranging from compositional analysis, global statistics of e-waste generation, and metallurgical processes applied for metals extraction from e-waste. This review critically analyses the existing studies to emphasize on the heterogeneity nature of e-waste, which has not been focused much in any of the existing review articles. Comprehensive analysis of conventional approaches such as pyrometallurgy and hydrometallurgy reveals that high costs and secondary pollution possibilities limit the industrial feasibilities of these processes. Therefore biohydrometallurgy, a green technology, has been attracting researchers to focus on this novel technique to implement it for metal extraction from WEEE.

Metabolic transcriptional analysis on copper tolerance in moderate thermophilic bioleaching microorganism Acidithiobacillus caldus

Bioleaching, an alternative environmental smelting technology, typically uses high concentrations of heavy metal ions, especially in the subsequent phase, due to metal ion accumulation from the mineral. In this study, we analyzed the overall response of the bioleaching microorganism Acidithiobacillus caldus to copper stress through physiological and transcriptomic analyses. Scanning electron microscopy results showed higher extracellular polymeric substances secretion and cell aggregation under copper stress. Intracellular levels of glutamic acid, glycine and cysteine increased, favoring the synthesis of glutathione for maintenance of the oxidation-reduction state. GSH, during copper stress conditions, the activity of GSH-PX and CAT increased, resulting in reduced oxidative damage while maintaining stable intracellular pH. Higher unsaturated and cyclopropane fatty acid levels resulted in increased membrane fluidity and compactness and decreased ATP levels to support the energy requirements for stress resistance. Initially, H⁺-ATPase activity increased to provide energy for proton output and decreased later at higher copper ion stress. From transcriptome analysis, 140 genes were differentially expressed under low copper stress (1 g/L), while 250 genes exhibited altered transcriptional levels at higher copper stress (3 g/L). These differentially expressed genes were involved primarily in metabolic pathways such as energy metabolism, two-component systems, amino acid metabolism, and signal transduction. The Sox family cluster gene cluster involved in the conversion of thiosulfate to sulfate was upregulated in the sulfur metabolism pathway. In the oxidative phosphorylation pathway, genes participating in the synthesis of NADH oxidoreductase and cytochrome c oxidase, nuoL, cyoABD (cyoA, cyoB and cyoD) and cydAB (cydA and cydB), were downregulated. The TCS element ompR, closely associated with the osmotic pressure, exhibited active response, while Cu²⁺ efflux system gene cusRS was upregulated. In the amino acid metabolism, the glnA involved in nitrogen fixation was upregulated and promoted the synthesis of glutamine synthetase for reducing excessive oxidative stress. This study provides new insights into the mechanism underlying A. caldus response to heavy-metal ion stress under harsh bioleaching conditions.

Metagenomic Insights into the Microbial Community Diversity between Leaching Heap and Acid Mine Drainage

The leaching heap and acid mine drainage are two key nodes in a bioleaching system. This study aimed to investigate the microbial community structural and functional diversity between the two nodes in bioleaching system from Dexing copper mine in Jiangxi province, China. 16SrRNA gene cloning and metagenomic analysis consistently indicated that there were obvious differences on microbial community structural and functional diversity in the two nodes. In leaching heap, the dominant species was the heterotrophic bacterium Acidiphilium; while the dominant species was the autotrophic bacterium Acidithiobacillus in acid mine drainage. Seven bacteria species were found in both two nodes, while the unique bacteria species in leaching heap and acid mine drainage were eleven and eight, respectively. In relation to the microbial community function aspect, all contigs and singlets were annotated against the non-redundant protein database of NCBI and clustering analyzed with COG database. For the two nodes, the COG clustering results showed that the functional category abundances were different, though the functional categories were similar. And the great majority of ORFs were forecasted as function unknown. All the results meant that the microbial community structural and functional diversity of bioleaching system was not as simple as former thought. This study could provide a new meta-view of theoretical support to bioleaching process.