Assessment of the scalability of a microtiter plate system for screening of oleaginous microorganisms

Applied Microbiology and Biotechnology - Recent developments in molecular biology and metabolic engineering have resulted in a large increase in the number of strains that need to be tested,...     

Ultra-sonication application in biodiesel production from heterotrophic oleaginous microorganisms

Utilization of microbial oil for biodiesel production has gained growing interest due to the increase in prices and the shortage of the oils and fats traditionally used in biodiesel production. However, it is still in the laboratory study stage due to the high cost of production. Employing organic wastes as raw materials to grow heterotrophic oleaginous microorganisms for further lipid production to produce biodiesel has been predicted to be a promising method for reducing costs. However, there are many obstacles including the low biodegradability of organic wastes, low lipid accumulation capacity of heterotrophic oleaginous microorganisms while using organic wastes, a great dependence on a high-energy consumption approach for biomass harvesting, utilization of toxic organic solvents for lipid extraction, and large amount of methanol required in trans-esterification and in-situ trans-esterifications. Ultra-sonication as a green technology has been extensively utilized to enhance bio-product production from organic wastes. In this article, ultra-sonication applications in biodiesel production steps with heterotrophic oleaginous microorganisms have been reviewed, and its impact, potential, and limitations on the process have been discussed.     

Continuous cultivation of microorganisms

This review presents selected studies on continuous cultivation including the genetics and selection of microorganisms, production of biomass, liquid fuels and other products, published in 1982-1984 and bearing a relationship to biotechnology.     

High-cell-density cultivation of microorganisms

High-cell-density cultivation (HCDC) is required to improve microbial biomass and product formation substantially. An overview of HCDC is given for microorganisms including bacteria, archae and eukarya (yeasts). Problems encountered by HCDC and their possible solutions are discussed. Improvements of strains, different types of bioreactors and cultivation strategies for successful HCDC are described. Stirred-tank reactors with and without cell retention, a dialysis-membrane reactor, a gas-lift reactor and a membrane cyclone reactor used for HCDC are outlined. Recently modified traditional feeding strategies and new ones are included, in particular those for unlimited growth to very dense cultures. Emphasis is placed on robust fermentation control because of the growing industrial interest in this field. Therefore, developments in the application of multivariate statistical control, artificial neural networks, fuzzy control and knowledge-based supervision (expert systems) are summarized. Recent advances using Escherichia coli– the pioneer organism for HCDC – are outlined. Received: 20 October 1998 / Received revision: 18 December 1998 / Accepted: 21 December 1998     

Advancing oleaginous microorganisms to produce lipid via metabolic engineering technology

With the depletion of global petroleum and its increasing price, biodiesel has been becoming one of the most promising biofuels for global fuels market. Researchers exploit oleaginous microorganisms for biodiesel production due to their short life cycle, less labor required, less affection by venue, and easier to scale up. Many oleaginous microorganisms can accumulate lipids, especially triacylglycerols (TAGs), which are the main materials for biodiesel production. This review is covering the related researches on different oleaginous microorganisms, such as yeast, mold, bacteria and microalgae, which might become the potential oil feedstocks for biodiesel production in the future, showing that biodiesel from oleaginous microorganisms has a great prospect in the development of biomass energy. Microbial oils biosynthesis process includes fatty acid synthesis approach and TAG synthesis approach. In addition, the strategies to increase lipids accumulation via metabolic engineering technology, involving the enhancement of fatty acid synthesis approach, the enhancement of TAG synthesis approach, the regulation of related TAG biosynthesis bypass approaches, the blocking of competing pathways and the multi-gene approach, are discussed in detail. It is suggested that DGAT and ME are the most promising targets for gene transformation, and reducing PEPC activity is observed to be beneficial for lipid production.     

Rapid assay for screening and characterizing microorganisms for the ability to degrade polychlorinated biphenyls

We designed a rapid assay that assesses the polychlorinated biphenyl (PCB)-degradative competence and congener specificity of aerobic microorganisms, identifies strains capable of degrading highly chlorinated biphenyls, and distinguishes among those that degrade PCBs by alternative pathways. Prior attempts to assay PCB-degradative competence by measuring disappearance of Aroclors (commercial PCB mixtures) have frequently produced false-positive findings because of volatilization, adsorption, or absorption losses. Furthermore, these assays have generally left the chemical nature of the competence obscure because of incomplete gas chromatographic resolution and uncertain identification of Aroclor peaks. We avoided these problems by using defined mixtures of PCB congeners and by adopting incubation and extraction methods that prevent physical loss of PCBs. Our assay mixtures include PCB congeners ranging from dichloro- to hexachlorobiphenyls and representing various structural classes, e.g., congeners chlorinated on a single ring (2,3-dichlorobiphenyl), blocked at 2,3 sites (2,5,2'5'-tetrachlorobiphenyl), blocked at 3,4 sites (4,4'-dichlorobiphenyl), and lacking adjacent unchlorinated sites (2,4,5,2',4',5'-hexachlorobiphenyl). The PCB-degrative ability of microorganisms is assessed by packed-column gas chromatographic analysis of these defined congener mixtures following 24-h incubation with resting cells. When tested with 25 environmental isolates, this assay revealed a broad range of PCB-degradative competence, highlighted differences in congener specificity and in the extent of degradation of individual congeners, predicted degradative competence on commercial PCBs, and (iv) identified strains with superior PCB-degradative ability.