Biological conversion of methane to liquid fuels: Status and opportunities

Methane is the main component of natural gas and biogas. As an abundant energy source, methane is crucial not only to meet current energy needs but also to achieve a sustainable energy future. Conversion of methane to liquid fuels provides energy-dense products and therefore reduces costs for storage, transportation, and distribution. Compared to thermochemical processes, biological conversion has advantages such as high conversion efficiency and using environmentally friendly processes. This paper is a comprehensive review of studies on three promising groups of microorganisms (methanotrophs, ammonia-oxidizing bacteria, and acetogens) that hold potential in converting methane to liquid fuels; their habitats, biochemical conversion mechanisms, performance in liquid fuels production, and genetic modification to enhance the conversion are also discussed. To date, methane-to-methanol conversion efficiencies (moles of methanol produced per mole methane consumed) of up to 80% have been reported. A number of issues that impede scale-up of this technology, such as mass transfer limitations of methane, inhibitory effects of H₂S in biogas, usage of expensive chemicals as electron donors, and lack of native strains capable of converting methane to liquid fuels other than methanol, are discussed. Future perspectives and strategies in addressing these challenges are also discussed.     

Biofuels in China: opportunities and challenges

With rapid economic development, energy consumption in China has tripled in the past 20 yr, exceeding 2.4 billion tons of standard coal in 2006. The search for new green energy as substitutes for the nonrenewable energy resources has become an urgent task. China has a variety of climates and is rich in potential biofuel plant species. Corn and cassava are used as the main raw materials for bioethanol production in China. At the end of 2005, bioethanol productivity had increased to 1.02 million tons produced by four companies, and bioethanol-blended petrol accounted for 20% of the total petrol consumption in China. According to the Mid- and Long-term Development Plan for Renewable Energy, the consumption of biodiesel in China will reach 0.2 million tons in 2010 and 2.0 million tons in 2020. This review is intended to provide an introduction to the distribution and development of biofuel crops and biofuel industry in China.     

ATP in current biotechnology: Regulation,applications and perspectives

Adenosine tri-phosphate (ATP), the most important energy source for metabolic reactions and pathways, plays a vital role in the growth of industrial strain and the production of target metabolites. In this review, current advances in manipulating ATP in industrial strains, including altering NADH availability, and regulating NADH oxidation pathway, oxygen supply, proton gradient, the electron transfer chain activity and the F₀F₁-ATPase activity, are summarized and discussed. By applying these strategies, optimal product concentrations, yields and productivity in industrial biotechnology have been achieved. Furthermore, the mechanisms by which ATP extends the substrate utilization spectra and enhances the ability to challenge harsh environmental stress have been elucidated. Finally, three critical issues related to ATP manipulation have been addressed.     

Characterization and fermentation of side streams from sulfite pulping

The fermentability of four different side streams produced in sulfite pulping has been compared in ethanol production with Saccharomyces cerevisiae. The results show that the fermentability of the different side streams varies, depending on where in the process they are produced, and the additional treatment applied to them. Side streams spent sulfite liquor, spent sulfite liquor derivative and spent sulfite liquor after ethanol fermentation that were fermentable benefited from the main cooking process, during which 90% of the sulfite was removed, whereas the side stream produced in the first cooking step, containing 11.0 g/L sulfite, was unfermentable. The fermentation of the side streams resulted in lower yields and productivity than fermentation in a defined medium. Furthermore, the fermentability of the side streams was improved after over-liming, evaporation, and laccase treatment. Over-liming was the most efficient means of detoxifying the side-streams, resulting in better fermentability. Sulfite treatment, however, had a counterproductive effect on fermentation due to the toxicity of this chemical to yeast metabolism. When the side-streams were detoxified by over-liming, loss of sugars was observed. Laccase treatment was less efficient, but it should be further explored as it offers a sustainable method of detoxifying side streams in situ.     

Ethanol production from lignocellulosic biomass of energy cane

Ethanol produced from lignocellulosic biomass is a renewable alternative to diminishing petroleum based liquid fuels. The release of many new sugarcane varieties by the United States Department of Agriculture to be used as energy crops is a promising feedstock alternative. Energy cane produces large amounts of biomass that can be easily transported, and production does not compete with food supply and prices because energy cane can be grown on marginal land instead of land for food crops. The purpose of this study was to evaluate energy cane for lignocellulosic ethanol production. Energy cane variety L 79-1002 was pretreated with weak sulfuric acid to remove lignin. In this study, 1.4 M sulfuric acid pretreated type II energy cane had a higher ethanol yield after fermentation by Klebsiella oxytoca without enzymatic saccharification than 0.8 M and 1.6 M sulfuric acid pretreated type II energy cane. Pretreated biomass was inoculated with K. oxytoca for cellulose fermentation and Pichia stipitis for hemicellulose fermentation under simultaneous saccahrification and fermentation (SSF) and separate hydrolysis and fermentation (SHF) conditions. For enzymatic saccharification of cellulose, the cellulase and ??-glucanase cocktail significantly increased ethanol production compared to the ethanol production of fermented acid pretreated energy cane without enzymatic saccharification. The results revealed that energy cane variety L 79-1002 produced maximum cellulosic ethanol under SHF (6995 mg/L) and produced 3624 mg/L ethanol from fermentation of hemicellulosic sugars.     

Sugarcane biotechnology: The challenges and opportunities

Summary Commercial sugarcane, belonging to the genus Saccharum (Poaceae), is an important industrial crop accounting for nearly 70% of sugar produced worldwide. Compared to other major crops, efforts to improve sugarcane are limited and relatively recent, with the first introduction of interspecific hybrids about 80 yr ago. Progress in traditional breeding of sugareane, a highly polyploid and frequently aneuploid plant, is impeded by its narrow gene pool, complex genome, poor fertility, and the long breeding/selection cycle. These constraints, however, make sugarcane a good candidate for molecular breeding. In the past decade considerable progress has been made in understanding and manipulating the sugarcane genome using various biotechnological and cell biological approaches. Notable among them are the creation of transgenic plants with improved agronomic or other important traits, advances in genomics and molecular markers, and progress in understanding the molecular aspects of sucrose transport and accumulation. More recently, substantial effort has been directed towards developing sugarcane as a biofactory for high-value products. While these achievements are commendable, a greater understanding of the sugarcane genome, and cell and whole plant physiology, will accelerate the implementation of commercially significant biotechnology outcomes. We anticipate that the rapid advancements in molecular biology and emerging biotechnology innovations would play a significant role in the future sugarcane crop improvement programs and offer many new opportunities to develop it as a new-generation industrial crop.     

Benefits of new tools in biotechnology to developing countries in south Asia: A perspective from UNESCO

South Asia, once considered as a laggard, has grown at about 6% on average over the past two decades and the current growth outlook is much brighter. However, this growth is not always well distributed and the challenges of institutionalising policies and mechanisms to ensure inclusive growth are now being seriously considered by these countries governments.The targets set by south Asian countries are primarily based on the investments in infrastructural sector with an objective to generate educated and skilled human resources. The other most important inclusive growth area is the core public services; Agriculture, Health, and Energy, which are increasingly becoming technology driven. Biotechnology has been increasingly seen now to be an area of technology that holds the greatest new potential to address problems arising from low productivity, overburdened health systems, high-cost unsustainable energy supplies and the need for developing new materials for industrial and environmental applications.This article attempts to highlight perspectives on some of the emerging areas of biotechnology that have good potential for economic development in the context of south Asia, as well as discuss briefly some of UNESCO's initiatives in biotechnology for that region.     

Albumin and mammalian cell culture: implications for biotechnology applications

Albumin has a long historical involvement in design of media for the successful culture of mammalian cells, in both the research and commercial fields. The potential application of albumins, bovine or human serum albumin, for cell culture is a by-product of the physico-chemical, biochemical and cell-specific properties of the molecule. In this review an analysis of these features of albumin leads to a consideration of the extracellular and intracellular actions of the molecule, and importantly the role of its interactions with numerous ligands or bioactive factors that influence the growth of cells in culture: these include hormones, growth factors, lipids, amino acids, metal ions, reactive oxygen and nitrogen species to name a few. The interaction of albumin with the cell in relation to these co-factors has a potential impact on metabolic and biosynthetic activity, cell proliferation and survival. Application of this knowledge to improve the performance in manufacturing biotechnology and in the emerging uses of cell culture for tissue engineering and stem cell derived therapies is an important prospect.     

Subcritical water and dilute acid pretreatments for bioethanol production from Melaleuca leucadendron shedding bark

The feasibility of bioethanol production using the lignocellulose of the shedding bark of Melaleuca leucadendron (Paper bark tree) was investigated. The effects of pretreatment parameters (temperature, time and acid concentration) on the yields of sugars and inhibitors, and optimal pretreatment conditions were determined. At very low severity conditions (combined severity factor, CSF ≤ 0.335), 28% of xylan was recovered and this recovery increased with increasing CSF till it peaked to 64.4% (11.2 g xylose L⁻¹) at a CSF of 1.475. However, at CSF > 2.0, xylose yield declined due to degradation. Mild and progressive glucose yield was detected in prehydrolysate at CSF ≥ 1.514, and subsequent enzymatic hydrolysis allowed complete glucan solubilization. Implementing environmentally friendly subcritical water pretreatment at CSF ≤ 0.335 on the shedding bark, about 85% of glucan solubilization was achieved after enzymatic hydrolysis. An industrial Saccharomyces cerevisiae strain readily fermented crude hydrolysate within 12 h, yielding 24.7 g L⁻¹ ethanol at an inoculum size of 2% (v/v), representing a glucose to ethanol conversion rate of 0.475 g g⁻¹ (91% ethanol yield). Based on our findings, the shedding bark is a potential feedstock for bio-ethanol production.     

Rumen microbiology, biotechnology and ruminant nutrition: The application of research findings to a complex microbial ecosystem

Research on rumen microorganisms has contributed greatly to our understanding of anaerobic microbial ecosystems, and has also influenced feeding practices and nutritional modelling with ruminants. However, it can be argued that rumen microbiology has not yet fulfilled its true potential. Growth-promoting ionophores, antibiotics and microbial feed additives were introduced before their microbiological effects had been determined. A more pro-active role for the microbiologist was predicted with the advent of recombinant DNA technology. Whether ventures in molecular biology can be applied successfully to benefit nutrition and health is likely to depend on whether means can be found for maintaining new strains in vivo.     

Biodiesel biorefinery: opportunities and challenges for microbial production of fuels and chemicals from glycerol waste

ABSTRACT: The considerable increase in biodiesel production worldwide in the last 5 years resulted in astoichiometric increased coproduction of crude glycerol. As an excess of crude glycerol hasbeen produced, its value on market was reduced and it is becoming a waste-stream insteadof a valuable coproduct. The development of biorefineries, i.e. production of chemicals andpower integrated with conversion processes of biomass into biofuels, has been singled out asa way to achieve economically viable production chains, valorize residues and coproducts,and reduce industrial waste disposal. In this sense, several alternatives aimed at the use ofcrude glycerol to produce fuels and chemicals by microbial fermentation have beenevaluated. This review summarizes different strategies employed to produce biofuels andchemicals (1,3-propanediol, 2,3-butanediol, ethanol, n-butanol, organic acids, polyols andothers) by microbial fermentation of glycerol. Initially, the industrial use of each chemical isbriefly presented; then we systematically summarize and discuss the different strategies toproduce each chemical, including selection and genetic engineering of producers, andoptimization of process conditions to improve yield and productivity. Finally, the impact ofthe developments obtained until now are placed in perspective and opportunities andchallenges for using crude glycerol to the development of biodiesel-based biorefineries areconsidered. In conclusion, the microbial fermentation of glycerol represents a remarkablealternative to add value to the biodiesel production chain helping the development ofbiorefineries, which will allow this biofuel to be more competitive.     

Chemicals from biotechnology: molecular plant genetics will challenge the chemical and the fermentation industry

 Industrial biotechnology has evolved as a significant manufacturing tool for products like fuel-grade ethanol, organic acids and bulk amino acids, but most items are still speciality products for food and pharmaceutical applications. Current development projects within the chemical industry, including lactic acid and 1,3-propanediol based polymers and plastics, indicate that new biotechnological processes and products may soon approach the market place, clearly targeted at the leading petrochemical bulk outlets. This is flanked by a strategic shift by the major chemical companies in to “life sciences”–pharmaceuticals, agrochemicals and the seed business as well as biotech fine chemicals. The recent tremendous achievements in molecular plant genetics and transgenic crop breeding will boost agro-biotechnology, agriculture and renewable raw materials as compelling projects for chemistry and biotechnology. New plant-based production routes may challenge established chemical and biochemical domains, but at the same time open new horizons to valuable feedstocks, intermediates and end-products. Received: 16 October 1998 / Received revision: 3 December 1998 / Accepted: 5 December 1998     

Progress in tissue culture,genetic transformation and applications of biotechnology to trees: an overview

Trees are an integral part of human life, and a vital component of biodiversity. Forest trees in particular are renewable sources of food, fodder, fuel wood, timber and other valuable non-timber products. Due to the rapid growth of population and the human desire to progress, there has been a tremendous reduction in forest cover from the earths surface. To maintain and sustain forest vegetation, conventional approaches have been exploited in the past for propagation and improvement. However, such efforts are confronted with several inherent bottlenecks. Biotechnological interventions for in vitro regeneration, mass micropropagation and gene transfer methods in forest tree species have been practised with success, especially in the last decade. Against the background of the limitations of long juvenile phases and life span, development of plant regeneration protocols and genetic engineering of tree species are gaining importance. Genetic engineering assumes additional significance, because of the possibility of introducing a desired gene in a single step for precision breeding of forest trees. There are no comprehensive and detailed reviews available combining research developments with major emphases on tissue culture and basic genetic transformation in tree species. The present communication attempts to overview the progress in tissue culture, genetic transformation and biotechnological applications in the last decade and future implications.     

Laboratory-scale ultrasound pre-treated digestion of sludge: Heat and energy balance

The objective of this work was to maximize the digestibility of biological sludge to elucidate the feasibility of a new sludge management strategy to recover good quality sludge for agricultural use. The combined effects of organic loading rates (from 0.7 to 2.8 g VS L⁻¹ d⁻¹) and the degree of disintegration by anaerobic digestion of sonicated activated sludge were discussed, and the thermal and energetic balances were evaluated. Despite low sonication inputs, sludge digestion performance improved in terms of solids degradation and biogas production depending on the soluble organic load. The biogas production by sonicated sludge was higher (up to 30%) with respect to the control. Filterability improved during digestion of sonicated sludge at medium OLR due to a significant abatement of the fines. Thermal balances indicated that sonication may be a proper system to guarantee self-sustaining WAS mesophilic digestion. Nevertheless, thickening is a pre-requisite to achieve a positive energy balance.     

Ethanol fermentation from lignocellulosic hydrolysate by a recombinant xylose- and cellooligosaccharide-assimilating yeast strain

The sulfuric acid hydrolysate of lignocellulosic biomass, such as wood chips, from the forest industry is an important material for fuel bioethanol production. In this study, we constructed a recombinant yeast strain that can ferment xylose and cellooligosaccharides by integrating genes for the intercellular expressions of xylose reductase and xylitol dehydrogenase from Pichia stipitis, and xylulokinase from Saccharomyces cerevisiae and a gene for displaying β-glucosidase from Aspergillus acleatus on the cell surface. In the fermentation of the sulfuric acid hydrolysate of wood chips, xylose and cellooligosaccharides were completely fermented after 36 h by the recombinant strain, and then about 30 g/l ethanol was produced from 73 g/l total sugar added at the beginning. In this case, the ethanol yield of this recombinant yeast was much higher than that of the control yeast. These results demonstrate that the fermentation of the lignocellulose hydrolysate is performed efficiently by the recombinant Saccharomyces strain with abilities for xylose assimilation and cellooligosaccharide degradation.     

Anaerobic digestion of source-segregated domestic food waste: Performance assessment by mass and energy balance

An anaerobic digester receiving food waste collected mainly from domestic kitchens was monitored over a period of 426 days. During this time information was gathered on the waste input material, the biogas production, and the digestate characteristics. A mass balance accounted for over 90% of the material entering the plant leaving as gaseous or digestate products. A comprehensive energy balance for the same period showed that for each tonne of input material the potential recoverable energy was 405 kWh. Biogas production in the digester was stable at 642 m³ tonne⁻¹ VS added with a methane content of around 62%. The nitrogen in the food waste input was on average 8.9 kg tonne⁻¹. This led to a high ammonia concentration in the digester which may have been responsible for the accumulation of volatile fatty acids that was also observed.