Recombinant DNA technology has allowed for the production of vaccines that offer protection without risk of infection e. Industrial microbiologists are actively involved in the development of these new vaccines. Microorganisms are also used to produce human or animal biologicals such as insulin, growth hormone, antibodies, and components for cosmetics.
They may also take part in identifying the organisms involved in and maintaining proprietary culture collections. There is a great deal of microbiology in the food and beverage industries. Some examples are:. Food Flavoring Agents and Preservatives: Organic acids, such as citric, malic, and ascorbic acids, and monosodium glutamate are microbial products commonly used in foods.
Foods: Mushrooms, truffles, and some red and green algae are consumed directly. Yeasts are used in food supplements for humans and animals. All of these require a microbiologist to insure product efficacy and quality. ENZYMES Industrial applications of enzymes include the production of cheese, the clarification of apple juice, the development of more efficient laundry detergents, pulp and paper production, and the treatment of sewage.
These processes have been dramatically enhanced by the use of recombinant DNA techniques to design enzymes and increased activity, stability, and specificity. The latter are also used for secondary oil recovery in oil fields and as lubricants in drilling oil wells, gelling agents in foods, and thickeners in both paints and foods. The microbiologist is involved in research on improvements in the production and detection of new metabolic pathways.
Microbiologists are also involved in the development of procedures for the control of deterioration in cosmetics, steel, rubber, textiles, paint, and petroleum products. The industrial microbiologist is directly involved in developing microbial strains to detoxify wastes of industrial, agricultural, or human origin. Extraction of minerals from low-grade ores is enhanced by some bacteria microbial leaching.
In addition, selective binding of metals by biohydrometallurgical processes is important in recycling of metals such as silver and uranium. You may become a skilled technician through on-the-job training, but many organizations require that a technician take career-related college level courses in order to advance to higher paying technical positions. Your guidance counselor may also be helpful in identifying college, industry, and government-sponsored summer enrichment program for high school or undergraduate students.
Students able to work on one or more research projects while an undergraduate student may have advantages when being considered for employment or graduate school. A person with a BS degree has several career options. One may begin a career in an industrial or clinical entry-level position. There may also be opportunities in sales of laboratory products or instruments.
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In many organizations, employees are encouraged to continue their educations. It may be possible in such an environment to obtain a higher degree while working full time. This means that the scientists will have the opportunity to advance to higher levels of responsibility either by staying in their chosen technical field or by assuming administrative responsibilities in technical management. As with most careers, an individual advances based on his or her unique approach to assigned tasks and contributions to achievements of his or her employer.
These positions may be in industry, government or academic situations. With the advanced degrees comes greater expectations for not only knowledge but increasing experiences with project design, conduct, and management. Multidisciplinary experiences are essential. Identification and monitoring of microbes involved in heap bioleaching processes.
Characteristics of microbes found in bioleaching processes. A number of review articles have been published that have described the physiologies and phylogenies of acidophilic micro-organisms in detail Rawlings, ; Rawlings and Johnson, ; Watling The major role of microorganisms in bioleaching processes is to catalyse the regeneration of ferric iron and protons, from ferrous iron and by sulphur oxidation respectively Rawlings and Johnson, Irrespective of whether tank or heap processes are used, the micro-organisms that catalyse biomining processes are required to grow in an essentially inorganic, aerobic, low pH environment.
The most important micro-organisms are autotrophic and utilize CO 2 as a carbon source. Although the exact nature of the energy sources may vary from mineral to mineral, the micro-organisms grow by oxidizing reduced forms of sulphur or ferrous iron, or both. The pH within tanks and heaps may also vary, but is highly acidic and typically within the range 1. The rather extreme conditions in stirred tanks and heaps mean that the number of micro-organisms that are likely to play a dominant role in biomining processes is limited Rawlings, It is important to note that in all pilot- and full-scale biomining operations that have been examined, microbial consortia mixed cultures rather than single cultures have been found Johnson, In general, the types of micro-organisms found in heap leaching processes are similar to those found in stirred tank processes.
At moderately thermophilic conditions At. Ferroplasma-like archaea seem to dominate Okibe et al. Thermophilic consortia are typically dominated by archaea with species of Sulfolobus, Acidianus, and Metallosphaera being most prominent Rawlings, Monitoring and identification of bioleaching microbes. Why do we need to monitor, quantify, and identify the microbes in heaps? It is accepted that differences in parameters such as temperature, pH, and aeration in different parts of the heap and at different times of the heap lifetime could have an effect on the populations present Johnson, Gaining a better understanding of the correlation between microbial types and numbers with changes in the chemical and physical profiles with time in the heap would be beneficial and could potentially assist in issues such as whether re-inoculation is necessary, which microbial cultures to add, whether the water quality is acceptable, and if the build-up of elements in the raffinate recycled to the heap could have an inhibitory effect on microbial performance.
The increased understanding of the adaptation of leaching bacteria to changing conditions could potentially be a step towards achieving faster start-up and increased metal extractions. While careful considerations are made in the design and engineering of heap bioleach operations, the microbiological aspects have been subjected to far less scrutiny and control Rawlings and Johnson, , and somewhat surprisingly, there have been relatively few accounts of the compositions and dynamics of microbial populations in biomining operations.
One reason for the dearth of information has been the lack of accurate and appropriate methods for analysing populations that are active in bioleaching environments. Until a few years ago, direct microbial counts and indirect measurements such as oxygen uptake rates, redox potential, pH, ferrous iron concentration, and temperature were used as an indication of the bulk activity of micro-organisms in the heap. In addition, microbial enrichments from solutions and ores have provided an initial view of micro-organisms associated with the process.
It was, however, not known whether these cultured strains were the key players in the process Brierley, ; Demergasso et al. The development of new culture-independent molecular techniques, such as polymerase chain reaction PCR , realtime quantitative PCR, denaturing gradient gel electrophoresis DGGE , and fluorescent in situ hybridization FISH , to detect and quantify populations, is a significant advancement, and these have become powerful tools to describe biodiversity and to follow changes in microbial consortia present in bioleaching systems without having to culture the micro-organisms Demergasso et al.
These techniques do not, however, give an account of the viability of the organisms, and recently a method for the rapid assessment of active biomass in leach liquors based on the measurement of ATP concentration in test solutions was described Okibe and Johnson, , which could be a simple way of quantifying microbial activity. A few examples of microbes identified in pilot- and commercial-scale heaps are presented in Table I. The results, in all cases, show the presence of a relatively small community of organisms, which is consistent with observations previously described Rawlings, ; Rawlings and Johnson, Studies on the microbiology of heap leach systems focus mainly on analyses of the liquid phases, i.
This is due mainly to practical problems of representative sampling of large areas and various depths of heaps, and of obtaining unbiased extraction of microbes or their DNA from the minerals and iron salt precipitates. Since the micro-organisms are not only present in the liquid fraction, but are also attached to the ore particle surfaces, it is important to include the attached population when assessing the microbial composition within the heap. To enable collection of representative data, sampling techniques will require further optimization through research and development.
Whether to inoculate and with which organisms? Microbial diversity is needed within a heap at different stages in its life cycle, and the challenge is to ensure that there is sufficient biodiversity within a heap to achieve optimal performance Rawlings and Johnson, Heap bioleaching operations typically rely on natural colonization by indigenous microbial strains. However, with the continued drive to achieve maximum metal recoveries in ever shorter times, the need arises to promote microbial colonization throughout the heap in the shortest time period possible, and also to maintain a population appropriate to the conditions established in the heap over time Watling, The question therefore arises whether one should only rely on the observation that iron- and sulphur-oxidizing micro-organisms are naturally ubiquitous, or should one inoculate a heap with organisms that are not likely to be present originally.
However, in the case of chalcopyrite heaps, which need to be operated at increased temperatures to achieve the necessary copper extraction rate, a consortium of micro-organisms that grow well over a range of temperatures from ambient to thermophilic is required. An additional inoculation step would therefore be required.
Geomicrobiology of the built environment
Examples of inoculation strategies described in literature are presented in Table II. This temperature gap must therefore be carefully managed to ensure that the heap temperature reaches the thermophilic zone at which chalcopyrite is amenable to effective bioleaching. Since the presence of temperature-sequential microbial populations that can facilitate the heating of the heap from mesophilic through to thermophile temperatures is critical Brierley, , inoculation with thermophiles several months before optimal conditions for their growth have developed in the heap could affect the survival of these organisms negatively, and a second round of inoculation with thermophiles would probably be required Dew et al.
The overall conclusion is that there would likely be a considerable time saving in inoculating a new heap with a microbial consortium or consortia at the appropriate points in time, rather than waiting for micro-organisms to grow naturally. Which micro-organisms to include in an inoculum is another challenge. Questions which have been debated over the years include 'Is there a superbug that will accelerate bioleaching processes?
Two contrasting approaches have been suggested and investigated to determine whether it would be possible to produce an ideal or optimized consortium of bioleaching micro-organisms for a given process or substrate Rawlings and Johnson, ; Johnson Mixed cultures containing additional acidophiles with complementary metabolic abilities, such as the ability to oxidize sulphur or to grow heterotrophically, are then compared.
The aim is to identify a microbial consortium that is not only highly efficient at catalysing the oxidative dissolution of target minerals, but which is also stable and robust. The 'top-down' approach utilizes an inoculum that contains a wide variety of different species and strains of acidophiles, on the basis that the species that are most fit for bioleaching a particular mineral concentrate will survive, while those that cannot compete are eliminated.
Bacteria and archaea that vary in e. Although interesting results were obtained, it seems highly unlikely that it would be possible to maintain such a consortium in a full-scale heap leach operation given the fact that these processes are open, non-sterile systems. The best one can probably do is to ensure that sufficient biodiversity is present in the solutions used to inoculate the heaps. Adaptation and genetic manipulation.
Adaptation of bacteria to different conditions, such as increased tolerance to high metal levels, is a simple means of genetic improvement. The technique is dependent upon the small number of errors in the DNA sequence that are made during chromosomal replication. Most errors are harmful or neutral, but some may be advantageous. Thus, when a selective pressure is applied to a population, those bacteria that acquire an advantageous mutation will outperform the rest and dominate the population.
For example, by growing bacteria in a continuous flow reactor under conditions of increasing flow rate, fast-growing bacteria will be enriched while slow-growing bacteria will be washed out. The advantage of 'mutation and selection' is that it can be applied in the laboratory without requiring specialized knowledge of bacterial physiology and biochemistry. The disadvantage is that it is a slow process and could take years to progress from environmental isolates to adaptation to rapid growth in highperformance biooxidation tanks Watling, ; Rawlings, Work began in the early s on the development of genetic systems for biomining micro-organisms.
Initially it was hoped that genetic engineering of biomining organisms would increase metal tolerance by insertion of genes resistant to metals that the organisms are currently sensitive to and reduction of certain metabolic bottlenecks by adding, for example, a more effective CO 2 -fixing enzyme Rawlings, Currently, however, the genetic engineering of mineral processing bacteria tends not to have a high priority among bioleaching researchers Watling, ; Rawlings, Reasons for this include:. There is some doubt that engineered strains would be sufficiently robust to survive and compete effectively in the complex, non-sterile, open environments of bioleaching processes.
There is a great deal of uncertainty about regulatory issues concerning the release of genetically engineered strains into the environment. Bioleaching processes operate best with a consortium of micro-organisms present, and if all members of the interdependent consortium have not been modified there may be no gain. In the case of heap leaching operations, these tend to be relatively low rate processes with an even greater diversity of microenvironments and micro-organisms.
Under such circumstances the advantage of genetic modifications is likely to be reduced. Genetic engineering may therefore have a much smaller role to play in biomining processes than originally envisaged. The main value of the development of genetic systems may lie in the ability to study the role and functions of different genes and their metabolisms, and will probably be important in the indirect improvement of bioleaching through an enhanced understanding of the genetics and physiology of the organisms, rather than directly by the addition of genetically manipulated micro-organisms to commercial processes.
Rawlings, Microbial tolerance to high metal and salt concentrations. An important characteristic of the acidophilic chemolithotrophs is their general tolerance of high concentrations of metallic and other ions. The fact that these organisms survive and thrive in bioleaching environments shows a remarkable ability to adapt to and tolerate the relatively high element concentrations they encounter.
In heap leach processes, the relatively large quantity of gangue compared to valuable metals, continuous recycle of the solution inventory, and the prolonged times of exposure in the absence of deliberate removal strategies can result in the release of considerable concentrations of gangue cations in the heap leach solution, to the point where they exceed limits commonly considered toxic to bioleaching microorganisms.
These values indicate that in every respect the solution conditions are far from what would be considered optimal in a typical bioleach operation. These salts create potentially adverse conditions for the microbial population and interfere with the microbial oxidation of ferrous iron, which is a critical sub-process in bioleaching. This could explain why in many heap bioleach operations the rate and extent of metal recovery remains below what could be achieved in theory, and it is postulated that this is due to the adverse solution conditions affecting microbial growth and activity Ojumu et al.
The importance of comprehensive laboratory evaluation during development of an ore body to commercial processing using biohydrometallurgy can therefore not be understated. Laboratory evaluation must include rigorous evaluation of the microbiological component and definition of operating parameters that engineers should bear in mind when designing the commercial plant. Failure to meet commercial production at a mine site can be the consequence of the incomplete understanding of the biological component of the process. One such example has been described by Brierley and Kuhn , where the inability of a copper bioleach process to meet the design criteria was in part due to a lack of sufficient testing to demonstrate the toxic effect of fluoride on the microbial component of the bioleach process.
A number of papers have recently been published describing the effect of fluoride toxicity on the performance of bioleaching micro-organisms Sundkvist et al. It has been observed that fluoride originating from gangue minerals effectively inhibits bioleaching at concentrations as low as 0. The toxicity effect increases at lower pH levels due to the formation of hydrogen fluoride, which can easily penetrate the bacterial cell membranes.
Aluminium, magnesium, and nitrate ions are often significant contributors to reduced water quality in bioleaching operations, and the potential inhibitory effect of Al and Mg on ferrous oxidation has been illustrated by amongst others Blight and Ralph and Ojumo et al. Ojumo et al.
Aluminium significantly reduces the amount of carbon biomass maintained in the reactor, whereas magnesium actually enhances it at low concentrations Ojumu et al. Similarly, the effect of high concentrations of Na 2 SO 4 on the growth rate of At. Blight and Ralph, , and Demergasso et al. Another major challenge faced by biomining companies, particularly those operating heaps in arid and semi-arid zones, is the quality of water used for irrigating the heaps. A high salt level is a significant problem in many areas but especially in the Western Australian and Chilean mineral processing industries.
The growth and activity of biomining micro-organisms is significantly reduced in the presence of salt, particularly chloride ions Zammit et al. The need to identify and characterize species and consortia of salt-tolerant mineral-oxidizing acidophiles has been recognized as a research priority and several papers referring to the isolation of salt-tolerant cultures with the ability to oxidize iron in the presence of NaCl have been published Davis-Belmar et al.
Microbial attachment to mineral surfaces. Attachment of micro-organisms to ore particles has been well proven and the attachment to metal sulphides and the formation of a biofilm is being viewed as critical for bioleaching performance Sand et al. It is now generally recognized and accepted that bioleaching is mainly a chemical process where ferric iron and protons are responsible for the leaching reactions.
The role of the microorganisms is to produce the leaching reagents and to create the space in which the leaching reactions take place. Microorganisms typically form an exopolysaccharide EPS layer when they adhere to the surface of a mineral. It is within this EPS layer rather than in the bulk solution that the oxidation reactions take place, as illustrated in Figure 1 , and therefore the EPS serves as the reaction space Rawlings, Thus, modelling the microbiology of the heap biooxidation process by considering solely the suspended microbial population would be deceptive.
In heap leach studies little attention has been paid to the investigation of microbial attachment as a means of mitigating heap bioleaching process difficulties. Aspects that could affect the performance of the microbes and the heap include initial microbial attachment to the ore, the development of firmly attached biofilms, the location of the microbial community with respect to the ore, and the kinetics of microbial growth on the ore surface and its subsequent impact on microbial ecology.
Recently the results from a number of studies investigating microbial attachment and colonization in heap bioleach environments were published. Africa et al. In another study by Chiume et al.
- Fritz Reiner, Maestro and Martinet.
- The Tower at Shark Valley (na).
It was demonstrated that the rate at which microbes multiply and attach to ore was influenced by the irrigation rate. In particular, the enhancement of microbial surface colonization at lower irrigation rates was observed, as illustrated by the increase in attached and interstitial cell numbers with time, implying that the effect on colonization should be borne in mind when specifying irrigation rates.
Bromfield et al. These results support the recommendations on inoculation strategies made in a previous section of this paper. The past two decades have witnessed exponential growth in the technological advancement and commercialization of heap bioleaching of copper ores, particularly of acid-soluble and secondary copper sulphides such as chalcocite.
The treatment of low-grade chalcopyrite ores using heap bioleaching is currently the focus of numerous research efforts. In the area of microbiology, the monitoring of microbial populations in heaps using a combination of molecular and culture-based techniques is now possible, and can provide an assessment of how microbial populations change in response to temperature and other heap conditions, especially important when treating chalcopyrite. Other aspects receiving attention include the mechanism of microbial attachment to mineral surfaces, the effect of process parameters such as irrigation rates on microbial colonization, the isolation and identification of salt-tolerant mineral-oxidizing acidophiles, and the effect of the build-up of elements such as sulphates, aluminium, and magnesium that could inhibit microbial performance.
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The value of genetic studies probably lies in the indirect improvement of bioleaching through an enhanced understanding of the genetics and physiology of the organisms, rather than directly by the addition of genetically manipulated micro-organisms to commercial processes.
Several strategies for the inoculation of heaps have been described and the overall conclusion is that there would likely be a considerable time saving in inoculating new heaps with a microbial consortium or consortia at the appropriate points in time, rather than waiting for micro-organisms to grow naturally.