Current Chemical Biology - Volume 6, Issue 1, 2012

Concerns about diminishing fossil fuel reserves along with the increasing levels of CO2 in the atmosphere are driving society towards the search for new renewable sources of energy. In this sense, biomass has the potential to significantly displace petroleum in the production of fuels and chemicals. Among the number of routes available today for the conversion of biomass into fuels and chemicals, new microbial technologies are currently experiencing a tremendous progress. The improvements in metabolic engineering (i.e. the alteration of inherent metabolic routes to favor production of desired products) and the vast knowledge acquired about the metabolic functioning of model microbes such as Escherichia coli and Saccharomyces cerevisiae are key findings that highlight the aforementioned success. The science of genetic manipulation of microorganisms has reached the point in which a designer microbe can be tailored for production of a specific fuel or chemical at concentrations, in many cases, high enough to reach commercial scale. In this special issue of Current Chemical Biology entitled “New biotechnologies for biofuels and advanced chemicals production” we, as Editors, have intended to select relevant works from worldwide respected and well-known leaders on this hot topic including Prof. Carol S. K. Lin (City University of Hong Kong), Prof. Chaitan Khosla (Stanford University, USA), Prof. Shota Atsumi (University of California, Davis, USA), Prof. Travis S. Bayer (Imperial College London, UK) and Prof. Xuefeng Lu (Key Laboratory of Biofuels, Qingdao, China). The editors were delighted to assemble such an outstanding list of contributors for the special issue and would like to thank deeply the authors and the journal for their cooperation and assistance during the past months. There is only one but most important thing left, the readers! The editors sincerely hope this special issue will be able to attract the attention of many readers in the field as well as introduce many others in the fascinating world of novel biotechnologies for advanced biofuels production, and look forward to enjoying further improvements in this area inspired (why not) by some of the contributions included in this issue. With my best wishes for a successful special issue.

Using fuels and chemicals derived from fossil sources underpins much of our everyday life and industrialized economy. However, obtaining carbon from oil and gas presents a number of environmental, economic, and political challenges. One solution to these challenges is to derive fuels and chemicals from renewable sources of carbon such as biomass or atmospheric carbon dioxide, thereby closing the carbon loop and moving towards a carbon neutral economy. Biological systems have evolved to harness carbon and energy from the environment for their own survival and can be engineered to produce fuels and chemicals. Although much progress has been made in this area, we present several challenges and areas of opportunity for development. We suggest that the primary barrier to large-scale commercialization of bioderived fuels and chemicals is the availability of feedstocks, which makes the conversion yield (feedstocks to fuels) a critical parameter in determining the impact and sustainability of biofuels processes. Engineering fuel-producing organisms to more efficiently capture carbon and energy, route metabolic fluxes to desired products, and tolerate industrial production conditions is a significant opportunity to increase the yields and economics of biofuels.

With increasing demand of energy, depletion of global fossil fuel reserves, and unsustainable emission rates of greenhouse gases, there is considerable impetus for the development of renewable fuel sources. Fatty acid derived biofuels, being energy-dense and compatible with existing infrastructure, represent a promising supplement to petroleum-based fuels. Earlier work has led to extensive genetic and biochemical characterization of the fatty acid biosynthesis pathway in Escherichia coli. More recently, the potential of using E. coli as a biocatalyst for converting biomass into fatty acid derivatives in an economically viable manner has been explored. In this article, we review the fatty acid biosynthesis pathway, and metabolic engineering efforts to manipulate the system for enhanced production of biodiesel, fatty alcohols, alkenes, and alkanes.

The unnerving price of petroleum will push a major change from a petroleum based economy to a natural feedstock based economy. Production of polyhydroxyalkanoates (PHAs) using industrial and agriculture by-products can allow the use of low-cost feedstock to produce materials with specific monomer composition and therefore, with the appropriate physicochemical properties to be used in a broad range of applications. Depending on the monomer composition, PHAs properties can range from thermoplastic to elastomeric materials. Even though PHA has been described as useful polymers due to thier intrinsic biodegradability and biocompatibility, their high price has limited their application significantly. The raw material cost has been known to contribute significantly to the manufacturing cost of PHA. Therefore, much research has been carried out using renewable cheap raw materials to replace the expensive commercial medium, which should reduce the overall production cost. In this review, the production of PHAs using low-cost sustainable raw materials such as molasses, whey, lignocelluloses, fats and oils, glycerol and wastewater are described. Finally, the physicochemical properties of PHAs produced from various carbon sources are discussed.

Cyanobacteria, photosynthetic bacteria with conversion capability to utilize solar energy and carbon dioxide and genetic engineering capacity to be easily modified to build non-native and improve native biosynthetic pathways, have displayed huge potential for biotechnology applications for direct production of biofuels by using solar energy as energy source and carbon dioxide as carbon source. Here research progress on microbial production of photosynthetic biofuels including hydrogen, ethanol, higher alcohols, isoprene and fatty acid-based biofuels in genetically engineered cyanobacteria is reviewed and the engineering challenges for using cyanobacteria as model hosts to make biofuels with high efficiency are discussed.

Biofuels synthesized from renewable resources are of increasing interest because of global energy and environmental problems. Compared to the traditional biofuel, ethanol, higher alcohols such as isobutanol and 1-butanol offer advantages such as higher energy density, lower hygroscopicity, lower vapor pressure, and compatibility with existing transportation infrastructure. Some Clostridia species are known to naturally produce isopropanol and 1-butanol. However, these fuels are not synthesized economically using native organisms. Additionally, other C3-C6 alcohols are not produced in large quantities by natural microorganisms. Synthetic biology offers an alternative approach in which synthetic pathways are engineered into user-friendly hosts for the production of these fuel molecules. These hosts could be readily manipulated to improve the production efficiency. This review summarizes recent progress in the engineering of microorganisms to produce C3-C6 alcohols.

The optimization of fructooligosaccharides (FOS) synthesis by immobilized fructosyltransferase from Rhodotorula sp. LEB-V10 was carried out on the basis of the experimental factorial design methodology, consisting of two consecutives (24-1) Fractional Factorial Design (FFD) for the following variable factors: temperature, pH, initial sucrose concentration and immobilized enzyme activity. The main target responses were FOS yield and FOS composition. It was observed that the increase of the immobilized enzyme activity resulted not only in a significant increase of the amount of nystose (GF3) in the FOS mixture but, it also increased the residual fructose concentration in the medium over time. Based on the results from the two FFD, the best conditions for pH and enzyme activity were 6.0 and 20 Ui/mL respectively. The final study step allowed the best conditions for synthesis temperature and sucrose concentration, being 48°C and 50% (w/v), respectively. Under these optimized conditions the total synthesis time was reduced from 96 h to 24 h, the conversion of sucrose was increased by 5% (YFOS = 0.58) and the composition of GF3 by 40% (φGF3 = 0.035).

MicroRNAs (miRNAs), which are highly conserved, non-coding endogenous RNA and nearly ∼22 nucleotides (nt) in length, have been widely reported to play the crucial roles in a number of pathological processes, most notably cancer. Hitherto, accumulating evidence has demonstrated that miRNAs are involved in mediating several cancer-related pathways linked to Programmed cell death (PCD), indicating that miRNAs may function as the key regulators in apoptosis and autophagy of cancer. In this review, we present a brief outline of the discovery, biosynthetic pathway and regulatory mechanisms of miRNAs, and further elucidate how miRNAs can regulate apoptotic and autophagic pathways as oncogenes or tumor suppressor genes in cancer. Together, these inspiring findings would help cancer biologists and clinicians uncover the mysterious landscape of miRNAs, thereby ultimately harnessing the miRNA-targeted PCD pathways for future cancer therapeutics.

Recent reports show that ordered mesoporous materials (OMM) are efficient as supports for the immobilization of enzymes. The advantageous textural, morphological and structural properties, the easy control of their parameters, and the interesting possibility of functionalizing the surface with a variety of organic groups, make them very promising supports for this application. We present in this mini-review a survey of our recent results on the use of different ordered mesoporous materials as supports for lipase. Related parameters are also studied and reviewed, namely size and shape of the pores (channel or cage/window) and the presence of hydrophobic groups on the pore surfaces. The procedure was conducted by grafting the siliceous materials with methyl groups through co-condensation. Two immobilization strategies were adopted: One is the post-synthesis approach, which is the immobilization on previously existing supports via electrostatic or hydrophobic interactions acting as the driving force that leads to immobilization. The other one is in situ approach, consisting of the entrapment of the enzyme within the inorganic matrix during its synthesis. Parameters like enzyme loading, catalytic activity, enzyme leaching or stability were studied for all the catalysts obtained. The relevance of the chemistry of surface and structure of the siliceous materials on the behavior and features of the catalysts obtained has been established.

There are number of methods used for detection of antioxidant activities. We have developed a new method using a compound (resazurin) which undergoes a visible colour shift by chemical or physical interaction with ascorbate and other antioxidant compounds. This novel method was developed to measure the antioxidant activity using the resazurin dye in microtitre- plate. The experiment protocol, which is rapid and inexpensive, ensures sensitivity and reproducibility in the measure of antioxidant activity of hydrophilic or water soluble antioxidant compounds. This method is able to achieve more accuracy in the determination of the minimum antioxidant concentration (MAC) values of natural products, including crude extract, chromatographic fractions or purified compounds comparing with ascorbic acid and other standard antioxidant. Therefore, in our opinion this procedure can quickly provide useful information on the antioxidant contents of foods and plants extracts using a very small sample quantity.

Wax esters have a variety of biotechnological usage in cosmetic and pharmaceutical products. Synthesized wax esters can be an alternative to sperm whale being rare. The ability of a non-commercial immobilized lipase from Rhizopus oryzae to catalyze the synthesis of wax esters was investigated in organic media. Wax esters were obtained by esterification of myristic, palmitic, stearic or oleic acids with cetyl alcohol. Response surface methodology was used to evaluate the effects of the temperature, the enzyme amount and the volume of hexane on the wax esters production yields. Under optimal conditions, high conversion yields (92-95%) of saturated fatty acids were reached within a reaction time of 30 min whereas a yield of 93.5% was obtained for cetyl oleate after 60 min. The synthesized esters were purified using a silica gel column. The immobilized Rhizopus oryzae lipase was successfully reused in 20 repeated cycles with no significant decrease in the final conversion yields. This makes it a promising candidate for the development of a highly effective set-up for the production of wax esters.

Copper has two key properties that make it an active ingredient in the medical devices currently being developed. First, copper is an essential trace element needed by humans, which plays a key role in many physiological processes in different tissues. For example, copper has been shown to be involved in angiogenesis and in wound healing. Second, copper has very potent antibacterial, antifungal, antiviral, and acaricidal properties. Recently, a novel technology has been developed that introduces copper oxide particles into polymeric materials, where they serve as a slow release source of copper ions. For example, by using this technology, copper oxide containing wound dressings that enhance wound healing; copper oxide containing antiviral respiratory masks that reduce the risk of infection; socks that protect from athlete's foot, and acaricidal bedding products that kill dust mites, have been developed. While copper oxide is used as the source of copper in mineral and vitamin supplements and is considered safe, its use in medical devices, as well as in industrial and consumer products, is novel. The current manuscript reviews the safety aspects of the use of copper oxide in products that come in contact with open and closed skin. Copper oxide products have been tested in 9 clinical trials and in several non-clinical studies and have been found to be non-irritating, non-sensitizing, and safe to use, with not even one adverse reaction recorded, both when in contact with intact and broken skin. This is in accordance with the extremely low risk of adverse reactions attributed to dermal exposure to copper.