Recovery of gold from industrial wastewater by extracellular proteins obtained from a thermophilic bacterium Tepidimonas fonticaldi AT-A2.

Biosorption has emerged as a promising alternative approach for treating wastewater with dilute metal contents in a green and cost effective way. In this study, extracellular proteins of an isolated thermophilic bacterium (Tepidimonas fonticaldi AT-A2) were used as biosorbent to recover precious metal (i.e., Au) from wastewater. The Au (III) adsorption capacity on the T. fonticaldi AT-A2 proteins was the highest when the pH was set at about 4.0-5.0. The adsorption capacity increased with increasing temperature from 15 to 70°C. Adsorption isotherm studies show that both Langmuir and Freundrich models could describe the adsorption equilibrium. The maximum adsorption capacity of Au (III) at 50°C and pH 5 could reach 9.7mg Au/mg protein. The protein-based biosorbent was also used for the recovery of Au from a wastewater containing 15mg/L of Au, achieving a high adsorption capacity of 1.45mg Au/mg protein and a removal efficiency of 71%.

Identification of Gold Sensing Peptide by Integrative Proteomics and a Bacterial Two-Component System.

The proteomics strategy was utilized to analyze and identify the gold adsorption proteins from Tepidimonas fonticaldi AT-A2, due to its outstanding performance in gold-binding and recovery. The results showed that three small proteins, including histidine biosynthesis protein (HisIE), iron donor protein (CyaY) and hypothetical protein_65aa, have a higher ability to adsorb gold ions because of the negatively charged domains or metal binding sites. On the other hand, the Salmonella PmrA/PmrB two-component system first replaces the iron (III)-binding motif using the peptide sequence from hypothetical protein_65aa, and this is then used to reveal the sensing and responsiveness to gold metal ions, which is totally different from the performance of traditional gold binding peptide (GBP) on the crystals on the surface of gold (111). We have successfully demonstrated an integrative proteomics and bacterial two-component system to explore the novel GBP. Finally, the heterologous over-expression of GBP by E. coli and the equilibrium of binding capacity for Au(III) have been conducted.

Recovery of high-value metals from geothermal sites by biosorption and bioaccumulation.

Generation of geothermal energy is associated with a significant amount of geothermal fluids, which may be abundant in high-value metals, such as lithium, cesium, rubidium, and other precious and rare earth metals. The recovery of high-value metals from geothermal fluids would thus have both economic and environmental benefits. The conventional technologies applied to achieve this are mostly physicochemical, which may be energy intensive, pose the risk of secondary pollution whilst being inefficient in recovering metals from dilute solutions. Biological methods, based on biosorption or bioaccumulation, have recently emerged as alternative approaches, as they are more environmentally friendly, cost effective, and suitable for treating wastewater with dilute metal contents. This article provides a comprehensive review of the related biological technologies used to recover the high-value metals present in geothermal fluids as well as critical discussion on the key issues that are often used to evaluate the effectiveness of those methods.

Tepidimonas fonticaldi sp. nov., a slightly thermophilic betaproteobacterium isolated from a hot spring.

A slightly thermophilic bacterial strain, designated AT-A2(T), was isolated from a hot spring water sample taken from the Antun hot spring in Taiwan and characterized using a polyphasic taxonomic approach. Cells of strain AT-A2(T) were aerobic, Gram-negative, motile by a single polar flagellum and formed non-pigmented colonies. Growth occurred at 35-60 °C (optimum, 55 °C), with 0-1.0 % NaCl (optimum, 0.2 %) and at pH 7.0-9.0 (optimum, pH 7.0). Phylogenetic analyses based on 16S rRNA gene sequences showed that strain AT-A2(T) belonged to the genus Tepidimonas and its closest neighbour was Tepidimonas thermarum AA-1(T) with a sequence similarity of 97.5 %. The predominant cellular fatty acids were C16 : 0 (40.2 %), summed feature 3 (C16 : 1ω7c and/or C16 : 1ω6c; 20.1 %) and C17 : 0 cyclo (11.5 %). The major respiratory quinone was Q-8. The polar lipid profile consisted of phosphatidylethanolamine, phosphatidylglycerol, diphosphatidylglycerol, an uncharacterized aminolipid and several uncharacterized phospholipids. The DNA G+C content of strain AT-A2(T) was 70.1 mol%. The mean level of DNA-DNA relatedness between strain AT-A2(T) and Tepidimonas thermarum AA-1(T) was 23.9 %. On the basis of the phylogenetic and phenotypic data, strain AT-A2(T) should be classified as representing a novel species, for which the name Tepidimonas fonticaldi sp. nov. is proposed. The type strain is AT-A2(T) ( = LMG 26746(T) = KCTC 23862(T) = BCRC 80391(T)).