Papers by Keyword: Microbial Ecology

Abstract: Previous agglomerate-scale heap bioleaching studies have outlined the variations in cell numbers of the liquid and attached phases during colonisation of sterilised ore by a pure culture. In this study, a mixed mesophilic culture was used in agglomerate-scale columns containing non-sterilised low-grade copper ore. Over a six - month period, columns were harvested at various intervals to provide snapshots of the metal distribution and the quantity, location, and ecological variations of mineral-oxidizing microbes within the ore bed. The initial colonisation period in this experiment was dissimilar to previous work, as the indigenous community was retained within the ore-bed throughout acid agglomeration. The overall colonisation phase lasted for approximately 1,000 hours until cell concentrations stabilised. In each column, less than 0.05% of the total cells were found in the leachate, 15-20% in the interstitial phase and the remaining ~80% were attached to the mineral surface. Once cell numbers had stabilised, interstitial cell concentrations were approximately 2,000× greater than those in the leachate. This difference persisted for the duration of the experiment. Copper concentrations in the two liquid phases generally decreased over time, but were on average 50× higher in the interstitial phase. Iron concentrations were more stable, but again were 30× higher in the interstitial phase. This demonstrates that that the difference in cell concentration between the leachate and interstitial phases cannot be explained through diffusion gradients within the system as it is much greater than those observed for the dissolved metals. It also shows that the specific environmental conditions of the interstitial and attached cells are very different to those inferred through analysis of leachates alone.

Abstract: Tank bioleaching of refractory sulphidic gold ores is well established, with potential to expand application to base metal concentrates. With increasing commercial tank bioleaching operations, understanding their microbial consortia is essential for process robustness. Recently, it has been shown that the consortia implicated in tank mineral bioleaching of gold-containing pyritic ores are dynamic, responding to the leaching environment. Factors driving the microbial dynamics of these consortia are under investigation, with emphasis also placed on determining the metabolic role of the key players in these consortia. Here, the combined influence of solids loading and organic carbon availability on microbial community dynamics and performance has been studied in agitated, aerated slurry bioreactors at 45°C. The control (autotrophic) and experimental (organic carbon added) reactors performed comparably at low solids loadings (4%, 7% and 10%). At 20% solids loadings, higher ferric iron concentrations (31 g/L vs 25g/L) and sulphide oxidation (66% vs 45%) were observed in the experimental reactor over the control. Under operating conditions used, a shift from bacterially-dominated cultures with L.ferriphilum as major species towards increasing archaeal abundance was observed. Archaeal abundance was higher in the organic carbon supplemented reactor at all solids loadings. The increased microbial diversity with organic supplementation appears to contribute to increased community robustness and associated leaching with increasing stress.

Abstract: The major goal of microbial ecology is to study the structure and function of complex microbial communities. Various bioinformatics software were employed to handle a large number of genomic information emerged by using high throughput sequencing. This paper summarizes application of bioinformatics in microbial ecology and their corresponding software used in α, β-diversity studies; and finally expounds the important roles in establishment of four synthesis databases.

Abstract: A novel industrial-scale bioreactor was implemented by Alcoa of Australia (Alcoa) at its Kwinana alumina refinery (Western Australia) for the degradation of oxalate, an organic byproduct of the Bayer alumina refining process. At the Kwinana refinery oxalate is removed from the Bayer Liquor via a separate side-stream as it increases the operating costs associated with the process and, at sufficiently high levels, may adversely affect the quality and yield of the final alumina product. The bioreactor process provides a more economic and environmentally friendly method for the treatment of removed oxalate compared with chemical conversion or storage of the solid by-product. In previous studies, the microbial community composition of the bioreactor was investigated and was found to be largely dominated by microorganisms of the α-, β- and γ-Proteobacteria subgroups. During the present study, two bacteria that had the ability to use oxalate as a sole source of carbon and energy were isolated from samples obtained from the bioreactor. Phylogenetic and physiological analyses indicated that the two isolates were probably strains of a novel species of a novel genus within the β-Proteobacteria subgroup. Isolation and characterisation of the microbial communities within the bioreactor system has the potential to improve process operation, which may have a positive impact on the biological oxalate destruction process and the footprint of alumina production.

Abstract: Rio Tinto, a natural extreme acidic environment with a rather constant acidic pH and a high concentration of heavy metals, is the product of the metabolic activity of chemolithotrophic microorganisms thriving in the rich complex sulfides of the Iberian Pyritic Belt. Up to now the microbial characterization has been made mainly in the water column and biofilm samples. Since all ferric reducing activities will not benefit the bioleaching operations, we consider it critical to ascertain the ecology and metabolic properties of the microorganisms inhabiting the anoxic part of the sediments, to facilitate the design and control the operation of heap bioleaching processes, maximizing their efficiency. The implication of these microorganisms in biohydrometallurgical operations is discussed.

Abstract: The paper “Bacterial succession in bioheap leaching” [1] initiated the search for methods to analyze the microbial dynamics in bioleaching industrial processes as a key to advancing commercial bioheap applications. “Chemical and physical conditions within bioheaps change radically from the time the bioheap is stacked and inoculated until bioleaching is completed.” The results from a comprehensive monitoring program by culturing and molecular techniques in an industrial bioleaching process for Run-of-mine (ROM) low grade copper sulfide ore in Chile will be summarized. The analysis of the compiled information permits an understanding of changes in microbial substrates availability, chemical and physical conditions. The impact of other aspects on microbiology, such as the mining programme and the industrial design are also considered. The bacterial succession in bioheap leaching solutions allowed the leaching cycle stages to be describe as: i) Acid conditioning and soluble copper releasing, ii) Chalcocite Bacterial leaching (ferrous oxidation); iii) Chalcocite Bacterial leaching (ferrous and reduced sulfur compounds –RSC- oxidation); iv) Bacterial leaching of sulphide minerals with higher rest potentials (pyrite and covellite ), v) Bacterial oxidation of remnant sulfide minerals and RSC.

Abstract: Black schist ores in Finland are often enriched with sulfide minerals, containing a variety of base metals such as nickel, copper, zinc and cobalt. As these ores are low grade with respect to the metals contained and the sulfide minerals cannot be effectively concentrated from the schists, they are currently being studied with regard to their suitability for bioleaching [1]. As part of this investigation, a large-scale column measuring 3 x 3 x 9 m was built and filled with 110 tons of the crushed black schist ore. A solution was circulated in the column for 95 weeks; this solution was adjusted to 1.8 prior to entry in the column and averaged 2.7 when leaving the column. During this time, approximately 22% of Mn, 10% of Ni and 5% of Zn were leached from the ore. Iron was also leached, but precipitated in the column. Any soluble iron in the effluent was mainly Fe (II). During this same time period, total cell counts averaged 3.6 x 107 cells/ml of effluent. On three different occasions over nearly a one-year period, culturable cells were enumerated on a variety of solid media [2] and represented only about 1% of the total cell counts. Of the culturable cells, ironoxidizing acidophiles (namely Acidithiobacillus ferrooxidans) far outnumbered any other acidophile by at least a factor of ten. Changes in populations were also monitored by molecular means (T-RFLP and SSCP) on five different occasions during the same year; again, populations in early samples were dominated by Acidithiobacillus ferrooxidans (at least two strains/sub-species). As the temperature of the column was increased from ~20 to 35°C by heating both the recirculated liquor and the air used for column aeration, the relative abundance of At. ferrooxidans-like bacteria decreased while the abundance of unidentified bacteria increased. Some of these bacteria have also been detected in lab-scale column experiments using the same ore [3]. Total cell counts varied little as the temperature increased, nor was there any change in the rate of metal leaching. It was apparent that even though the leaching of metals from black schist ores was not greatly influenced by increases of temperature in the column, active microbial populations were present and were influenced by temperature.