Leaching of copper converter slag withAspergillus niger culture filtrate

Leaching of copper converter slag of M/s Hindustan Copper Ltd, Ghatshila (Bihar, India) was carried out usingAspergillus niger culture filtrate. The effects of the duration of leaching, temperature, pulp density and the addition of hydrochloric acid were studied.A. niger culture filtrate solubilized metals from the converter slag at levels of 18.70% copper, 7.40% nickel and 4.00% cobalt. Addition of hydrochloric acid was found to improve copper, nickel and cobalt solubilization to 46.52, 27.90 and 37.96%, respectively. HPLC analysis of the fungal culture filtrate revealed the presence of succinic and citric acids. Therefore, leaching of the slag was also carried out with matching concentrations of these organic acids individually as well as with both mixed together. Results are discussed.     

Study on reaction mechanism of bioleaching of nickel and cobalt from lateritic chromite overburdens

Depletion of high-grade ores and presence of significant quantities of metals in low-grade oxide ores has enforced to utilize the overburdens (COB) and wastes (low-grade ores) generated during mining operations. The impact of ore mineralogy and mineral–microbe interaction during bioleaching could not be ignored. Seeking to the need, a systematic study was performed to establish the reaction mechanism involved for recovery of nickel and cobalt from chromite overburden (COB), Sukinda, Orissa using pure culture of Aspergillus niger. Mineralogical analysis reveals a complete conversion of goethite into hematite phase leading to exposure of nickel particles into the micro-pores and cracks developed in the matrix which was initially found to be intertwined in the goethite lattice. As a result, it became more susceptible to attack by the fungal bio acids which in turn accelerate the dissolution rate. Organic acids like oxalic and citric acids were detected in the culture filtrate using HPLC. TEM analysis of the leached samples shows that nickel dissolute into the solution leaving a porous space in the matrix of the hematite by forming nickel oxalate or nickel citrate. Kinetics of the nickel bioleaching was studied to support the mechanism of the reaction. It was observed that the initial rate of reaction follows the chemical control dissolution reaction where as the later part fits to shrinking core model. 18% of nickel and 37.8% of cobalt was recovered from pre-treated COB at 2.5% pulp-density with 10% (v/v) fungal inoculum at 30 °C within 25 days in shake flask while 32.5% of nickel and 86% of cobalt was recovered in bioreactor.     

Microbial leaching of lateritic nickel ore

Lateritic nickel ore from the Sukinda Mines, Orissa, India, was leached using Thiobacillus ferrooxidans, Bacillus circulans, Bacillus licheniformis and Aspergillus niger at 5% (w/v) solid: liquid ratio for 5–20 days. Maximum leaching of Ni was achieved with B. circulans (85%) and Aspergillus niger (92%) after 20 days. Bacillus circulans showed significantly higher rate of leaching than the other organisms giving 80% Ni extraction after 15 days. The importance and usefulness of heterotrophic organisms in metal extraction are discussed.     

Laugung lateritischer Nickelerze mit heterotrophen Mikroorganismen

Organic acids that are excreted by microorganisms dissolve nickel from lateritic ores. In chemical leaching experiments, fifteen organic acids were tested in the concentration range of 0.05–0.5 M. The most effective were hydroxycarboxylic acids. The leaching of nickel is dependent on the type of mineralization. With completely limonitized ore, no mobilization occurred, while up to 90% of the nickel was extracted from silicate-bearing laterites by 0.5 M citric acid. In biological leaching tests, Penicillium was found to be the most effective microorganism. After improvement of the leaching conditions, up to 70% of the nickel was extracted at considerably lower citric acid concentrations than with the chemical leaching process. Generally, leaching of nickel from lateritic ores with heterotrophic microorganisms is possible and seems to be promising. Possibilities for future investigations are discussed.     

Continuous production of citric acid from dairy wastewater using immobilized<Emphasis Type="Italic">Aspergillus niger</Emphasis> ATCC 9142

The continuous production of citric acid from dairy wastewater was investigated using calcium-alginate immobilizedAspergillus niger ATCC 9142. The citric acid productivity and yield were strongly affected by the culture conditions. The optimal pH, temperature, and dilution rate were 3.0, 30°C, and 0.025 h⁻¹, respectively. Under optimal culture conditions, the maximum productivity, concentration, and yield of citric acid produced by the calcium-alginate immobilizedAspergillus niger were 160 mg L⁻¹ h⁻¹, 4.5 g/L, and 70.3% respectively. The culture was continuously perfored for 20 days without any apparent loss in citric acid productivity. Conversely, under the same conditions with a batch shake-flask culture, the maximum productivity, citric acid concentration, and yield were only 63.3 mg L⁻¹ h⁻¹, 4.7 g/L and 51.4%, respectively. Therefore, the results suggest that the bioreactor used in this study could be potentially used for continuous citric acid production from dairy wastewater by applying calcium-alginate immobilizedAspergillus niger.     

Ram horn peptone as a source of citric acid production by <Emphasis Type="Italic">Aspergillus niger</Emphasis>, with a process

The present study deals with the production of citric acid from a ram horn peptone (RHP) by Aspergillus niger NRRL 330. A medium from RHP and a control medium (CM) were compared for citric acid production using A. niger in a batch culture. For this purpose, first, RHP was produced. Ram horns were hydrolyzed by treatment with acids (6 N H₂SO₄, 6 N HCl) and neutralizing solutions. The amounts of protein, nitrogen, ash, some minerals, total sugars, total lipids and amino acids of the RHP were determined. RHP was compared with peptones with a bacto-tryptone from casein and other peptones. The results from RHP were similar to those of standard peptones. The optimal concentration of RHP for the production of citric acid was found to be 4% (w/w). A medium prepared from 4% RHP was termed ram horn peptone medium (RHPM). In comparison with CM, the content of citric acid in RHPM broth (84 g/l) over 6 days was 35% higher than that in CM broth (62 g/l). These results show that citric acid can be produced efficiently by A. niger from ram horn.     

Repeated batch production of citric acid from sugarcane molasses using recycled solid-state surface culture ofAspergillus niger

Summary The recycled solid-state surface fermentation (SSF) culture ofAspergillus niger KCU520 was used for repeated batch production of citric acid from sugarcane molasses. The rate of citric acid production was doubled, reducing the fermentation time to half, compared to the normal single cycle batch submerged or surface fermentation process. About 80% sugar was converted to citric acid in five-day batch fermentation and three batches were carried out with the same fungal mat without any significant loss of productivity.     

Microbial community study of the iron ore concentrate of the Sishen Iron Ore Mine, South Africa

As a result of the advancing global technologies and civilisation, there has been a progressive depletion of high-grade mineral deposits. Consequently, it has become increasingly important to process lower-grade ores. Phosphorous (P) and particular potassium (K) contained in the iron ore concentrates of the Sishen Iron Ore Mine have a detrimental effect on the steel making process, whereby these alkali’s cause cracks to form in the refractory lining of blast furnaces. It is initially essential to determine which microbes are indigenously present at the Sishen Iron Ore Mine before strategising how best to employ them to industrial advantage. Therefore, the objective of this study was to determine which microorganisms are indigenous to the iron ore and soil of the Sishen Iron Ore Mine. The bacterial 16S PCR and fungal ITS PCR revealed several bacterial and fungal species present in the mine environment. The bacterial isolates were found to be closely related to Herbaspirillum species, as well as Acidithiobacillus ferrooxidans, while the fungal isolates were closely related to Aureobasidium pullulans, Phaeosphaeria nodorum, Aspergillus fumigatus, and Candida parapsilosis. Isolating A. fumigatus from the iron ore/soil of the mine may indicate that A. niger, the most common fungi used for the production of citric acid, can adapt to the stringent mine environment. This would allow the application of A. niger for the production of citric acid, which may be used for the chemical leaching of the P and K from the iron ore concentrate of the Sishen Iron Ore Mine.     

The kinetic basis of the role of Ca++ ions for higher yield of citric acid in a repeated-batch cultivation system

The present investigation deals with role of Ca⁺⁺ ions in increasing the yield of citric acid in a repeated-batch cultivation system (working volume 9-1) and its kinetic basis. Five different hyper-producing strains of Aspergillus niger were evaluated for citric acid production using clarified cane-molasses as basal substrate. Among the cultures, NG^GCB101 (developed by u.v./chemical mutation in our labs) gave maximum production of citric acid i.e., 87.98 g/1, 6 days after mycelial inoculation. The addition of CaCl₂ to the culture medium promoted the formation of small rounded fluffy pellets (1.55 mm, diameter), which were desirable for citric acid productivity. CaCl₂ at a level of 2.0 M, added during inoculation time, was optimized for commercial exploitation of molasses. During repeated-batch culturing, a yield of citric acid monohydrate of 128.68 g/1 was obtained when the sampling vs. substrate feeding was maintained at 4-1 (44.50% working volume). The incubation period was reduced from 6 to only 2 days. The values of kinetic parameters such as substrate consumption and product formation rates revealed the hyperproducibility of citric acid by the selected Aspergillus niger NG^GCB101 (LSD = 0.456a, HS). Case studies are highly economical because of higher yield of product, lower energy consumption and the use of raw substrate without any additional supplementation.     

Extraction of Zinc from Industrial Waste by a Penicillium sp

Zinc was extracted from a filter residue of a copper works (58.6% zinc) by a Penicillium sp. isolated from a metal-containing location. By isotachophoresis citric acid was identified as the leaching agent. Citrate was only formed when the leaching substrate was present. This production of citrate was different in several ways from that achieved by Aspergillus niger: glucose was utilized before fructose; the initial concentration of zinc was 50 to 500 times higher than usual in citrate fermentations with A. niger; citrate production stopped when 80 to 90% of the zinc was leached, although sufficient sugar for further synthesis was still present; and in synthetic media citrate production by A. niger needs an acidic environment (pH 2), while the formation of citric acid by Penicillium sp. occurred in a pH range of 7 to 4. Tests with different concentrations of waste material (0.5, 2.5, and 5%) showed that the highest yield of solubilized zinc occurred with a 2.5% substrate (93% zinc extracted after 13 days).     

基于DNA高通量测序分析生料酿醋过程中的真菌多样性

【目的】了解生料酿醋不同阶段的真菌群落结构及其变化规律,为生料酿醋工艺优化提供理论指导。【方法】从山西一家生料酿醋企业采集原料、麸曲、发酵缸醋醅、熏醋样、淋醋样等涉及生料酿醋各阶段的样品共51份,扩增真菌ITS1区序列并利用高通量测序技术分析真菌多样性。【结果】除5份样品未扩增成功外,在剩余46份样品中共检测到489个真菌OTU,以子囊菌为主(占88.3%)。原料、麸曲、发酵缸醋醅、熏醋样、淋醋样等不同组别间在真菌群落结构方面存在显著差异。原料和麸曲中的真菌物种丰富度最低,发酵缸醋醅的真菌物种丰富度最高,熏醋样和淋醋样中的真菌物种丰富度又有所降低。原料和麸曲中的优势真菌分别为酿酒酵母和黑曲霉,是发酵阶段真菌的重要来源,但发酵缸醋醅中也检测到大量可能来源于发酵室环境的真菌。发酵缸醋醅在不同发酵时期间也存在明显的真菌群落结构差异,并可据此划分成发酵前期(包括发酵第2–13天的样品)和发酵后期(包括发酵第17–46天的样品)。酿酒酵母和亮白曲霉的丰度在发酵前期显著高于发酵后期,而黑曲霉、一种小戴卫霉科真菌等的丰度在发酵后期显著高于发酵前期。【结论】生料酿醋的不同阶段和发酵缸醋醅发酵的不同时期,其真菌群落结构都存在明显差异。酿酒酵母和黑曲霉是发酵阶段的优势真菌。本研究为生料酿醋工艺优化提供了理论依据。     

Short communication: Influence of inoculum preparation on citric acid production by Aspergillus niger

The type of sporulation medium and time of incubation had an effect on spore viability and citric acid production by mycelia grown from Aspergillus niger spores. Shu & Johnson agar (SJA) and potato dextrose agar gave higher citric acid titres than malt-extract agar. SJA also gave better germinability than the other media. Viability increased with time of incubation, but higher production of citric acid was achieved with spores incubated for less than 7 days.     

Solubilization of Magnesium-Bearing Silicate Minerals and the Subsequent Formation of Glushinskite by Aspergillus niger

Microbes may play a substantial role in the weathering and alteration of minerals. However, not enough concerns have been realized about the complexity of microbe-mineral interactions. The present work reports the interactions between fungi and minerals with emphasis on the role of silicate minerals as the metal donor for the precipitation of secondary mineral. Herein, two magnesium-bearing silicate minerals with different structures, forsterite and talc, were added to the submerged cultures of Aspergillus niger (A. niger). It is shown that forsterite exhibits a better solubilization effect than talc, and the secondary mineral glushinskite only precipitates in the presence of forsterite substrates. Oxalic acid excreted by A. niger plays a key role in the biological leaching and mineralization processes. Moreover, the forsterite particles with certain size added to the cultures tend to inhibit the aggregation of fungal biomass, and therefore affect the morphology of A. niger aggregates in the submerged culture. With varying forsterite particle size, distinct fungal morphological forms including mycelial pellets and freely dispersed hyphae can be formed, which have a direct impact on fungal metabolism and ultimately result in varied crystallization habits of the neo-minerals. Particularly in the culture with ?40/+60 mesh forsterite particles, the mineralized glushinskite mainly exhibit tubular forms; whereas when forsterite particles were at ?100/+120 mesh or ?200 mesh, pyramidal prisms are obtained. We show that the environmental factors such as the particle size of mineral substrate could influence the fungal morphology and metabolic activities, thereby leading to different morphological neo-minerals. The dependence of biomineral morphology on the environmental factors can open up a novel avenue to understanding the microorganism-environment interactions.     

Bioleaching and bioprecipitation of nickel and iron from laterites

Abstract: Leaching of silicate ores, particularly nickel laterites, with the aid of heterotrophic organisms has been briefly reviewed. Samples of laterite ores from Greece were characterised mineralogically and a number of microorganisms isolated from them. One of these organisms (code FI) was successfully acclimatized to 6400 ppm nickel. Samples of the high-grade Greek Kastoria nickel laterite were leached with sulphuric acid and a number of organic acids. Sulphuric and citric acids extracted over 60 and 40% of the contained nickel, respectively, but the other acids employed were less efficient leachants. Oxalic acid precipitated nickel oxalate. Roughly the same extraction of iron was observed. The main leaching parameter was confirmed to be hydrogen ion concentration, although complexation with organic anions was a contributor. Organism FI (a strain of Penicillium ) was used in comparison with organisms from various culture collections to bioleach nickel from samples of the low-grade Greek Litharakia nickel laterite. The organisms were cultivated in a mixture of a sugar-based nutrient mineral medium and finely ground ore. Several penicillia and aspergilli leached 55–60% of the contained nickel and cobalt, and 25–35% of the iron when sucrose was the carbon source, but FI was not efficient. However, in molasses medium, Fl extracted nearly 40% of the nickel. Biosorption and bioprecipitation reactions were observed. The mechanism of bioleaching or in situ leaching is discussed in terms of close physical and chemical association between the fungal hyphae and mineral phases in the ore. This accounted for the low overall hydrogen ion concentration observed during bioleaching.     

Mutation of Aspergillus niger for hyperproduction of citric acid from black strap molasses

Spore suspensions of Aspergillus niger GCB 75, which produced 31.1 g/l citric acid from 15% sugars in molasses, were subjected to u.v.-induced mutagenesis. Among three variants, GCM 45 was found to be the best citric acid producer and was further improved by chemical mutagenesis using NTG. Out of 3 deoxy-D-glucose-resistant variants, GCM 7 was selected as the best mutant which produced 86.1 ± 1.5 g/l citric acid after 168 h of fermentation of potassium ferricyanide + H₂SO₄-pretreated black strap molasses (containing 150 g sugars/l) in Vogel's medium. On the basis of comparison of kinetic parameters, namely the volumetric substrate uptake rate (Q _s), and specific substrate uptake rate (q _s), the volumetric productivity, theoretical yield and specific product formation rate, it was observed that the mutants were faster growing organisms and had the ability to overproduce citric acid.     

Biochemical studies of citric acid production and accumulation by Aspergillus niger mutants

The biochemical rationale for the inhibition of citric acid fermentation by Aspergillus niger in the presence of Mn²⁺ ions has been investigated using high citric acid-yielding, Mn²⁺ ion-sensitive as well as Mn²⁺ ion-tolerant mutant strains of A. niger. In the presence of Mn²⁺ (1.5 mg/l), citric acid production by the Mn²⁺ ion-sensitive strain (KCU 520) was reduced by about 75% with no apparent effect on citric acid yield by the Mn²⁺ ion-tolerant mutant strain (GS-III) of A. niger. The significantly increased level of the Mn²⁺ ion-requiring NADP⁺-isocitrate dehydrogenase activity in KCU 520 cells and the lack of effect on the activity level of the enzyme in GS-III mutant cells by Mn²⁺ ions during fermentation seem to be responsible for the Mn²⁺ ion inhibition of citric acid production by the KCU 520 strain and the high citric acid yield by the mutant strain GS-III of A. niger even in the presence of Mn²⁺.     

Characterization of metabolically active developmental stage of Aspergillus niger cells immobilized in polyacrylamide gel

Summary The in-situ development of Aspergillus niger entrapped in polyacrylamide gel from spores and the gel surface characteristics were studied during the repeated shake flask batch citric acid fermentation. A marked increase in the rate of citric acid production was observed with the periodic replacement of culture with fresh media at an interval of 6 days reducing the fermentation time nearly to half. The metabolically active A. niger cells for citric acid production were characterized by the appearance of thick and bulbous hyphae scattered in and on the gel surface.     

Influence of pectin and glucose on growth and polygalacturonase production by Aspergillus niger in solid-state cultivation

The solid-state production of endo- and exo-polygalacturonases (PG) by Aspergillus niger was studied in a media containing wheat bran, salts, and different citric pectin and/or glucose concentrations. Kinetic analysis of the process indicated that the formation of PG and the growth of A. niger are associated processes. By increasing citric pectin from 0 to 16% (w/w), the maximum A. niger concentration (X _m) was raised from 94 to 121 mg/g dry medium suggesting that pectin can be used by A. niger as a growth substrate besides its role as an inducer. With 16% (w/w) pectin, 281 U exo-PG/gdm and 152 U endo-PG/gdm were obtained. Otherwise, pectin concentrations from 20 to 30% (w/w) hindered both production and growth. A. niger concentrations of 108–113 mg/gdm were achieved in runs with glucose from 5 to 12% (w/w), whereas at 16 and 20% (w/w) glucose, lower X _m values (ca. 100 mg/gdm) were measured. The addition of glucose to the wheat bran medium, up to 10% (w/w) led to maximum endo-PG titers slightly lower than those found in the absence of glucose. Nevertheless, exo-PG formation in these media was strongly increased and activities over 370 U/gdm were achieved. The results suggest that in experiments with pectin concentrations until 16% (w/w), exo-PG production was repressed by pectin-degradation products although these same substances had favored biomass growth. When glucose concentrations over 10% (w/w) were added to the media, the maximum activities of both enzymes decreased drastically, suggesting that glucose at high concentrations also exerts a repressive effect on PG production.     

Development of a serial bioreactor system for direct ethanol production from starch using<Emphasis Type="Italic">Aspergillus niger</Emphasis> and<Emphasis Type="Italic">Saccharomyces cerevisiae</Emphasis>

Aspergillus niger hyphae were found to grow with unliquefied potato starch under aerobic conditions, but did not grow under anaerobic conditions. The raw culture ofA. niger catalyzed saccharification of potato starch to glucose, producing approximately 12 g glucose/L/day/ The extracellular enzyme activity was decreased in proportion to incubation time, and approximately 64% of initial activity was maintained after 3 days. At 50°C,A. niger hyphae growth stopped, while the extracellular enzyme activity peaked. On the basis of theA. niger growth property and enzyme activity, we designed a serial bioreactor system composed of four different reactors. Fungal hyphae were cultivated in reactor I at 30°C, uniquefied starch was saccharified to glycose by a fungal hyphae culture in reactors II and III at 50°C, and glucose was fermented to ethanol bySaccharomyces cerevisiae in reactor IV. The total glucose produced by fungal hyphae in reactor I and saccharification in reactor II was about 42 g/L/day. Ethanol production in reactor IV was approximately 22 g/L/day, which corresponds to about 79% of the theoretical maximum produced from 55 g starch/L/day.     

Bioleaching of Heavy Metals from Mine Tailings by Aspergillus fumigatus

The bioleaching experiment was conducted for the removal of heavy metals from mine tailings. A fungal strain was isolated from the gold mine tailings and it has been identified as Aspergillus fumigatus based on its 18S rDNA analysis. Bioleaching using A. fumigatus was carried out in bioleaching step processes (one-step and two-step) at various tailings concentrations (1%, 2%, 4%, and 8% [w/v]). In the one-step bioleaching process where fungi were cultivated in the presence of the tailings, concentration of oxalic acid was the highest among the organic acids produced. On the other hand, in the two-step bioleaching process where the metabolic products of fungal growth, which have been separated from its biomass, were used, citric acid was dominant. In the one-step process, the highest As (62%), Fe (58%), Mn (100%), and Zn (54%) removals were observed at the lowest tailings concentration (1%). The removal of Pb at 1% tailings concentration in the one-step process was 56%, whereas 88% removal was achieved in the two-step process where citric acid was dominant. In general, heavy metals removal efficiency decreased with increased tailings of the concentration in both bioleaching processes. This study shows the possibility of using A. fumigatus to bioleach hazardous heavy meals from gold mine tailings.