Microbiological production of tocopherols: current state and prospects

Tocopherols are antioxidants that prevent various diseases caused by oxidative stress. Tocochromanols comprise four isoforms of tocopherols and four isoforms of tocotrienols but α-tocopherol is the most abundant and active isoform in human and animal tissues. Tocopherols are used as dietary supplements for human, as food preservatives, in manufacture of cosmetics, and for fortification of animal feed. Only photosynthetic cells are known to accumulate detectable concentrations of tocopherols. Tocopherols can be extracted and purified or concentrated from vegetable oils and other higher plant materials. However, the concentrations in these higher plant materials are very low and there are high proportions of the less-active homologues of tocopherols. Among the many strains of photosynthetic microorganisms known to accumulate tocopherols, Euglena gracilis is promising for commercial production of α-tocopherol. The growth rate and α-tocopherol contents are relatively high and α-tocopherol comprise more than 97% of all the tocopherols accumulated by Euglena gracilis. Although a lot of work has been done to increase the contents and composition of tocopherols in higher plants through genetic and metabolic engineering, work on genetic modification of microorganisms for increased tocopherol accumulation is scarce. Many cultivation systems have been investigated for efficient production of tocopherol by Euglena gracilis. However, those that involve heterotrophic metabolism are more promising. Bubble columns and flat-plate photobioreactors are more suitable for commercial production of tocopherols, than the tubular, internally illuminated, and open-air photobioreactors.     

Cause or effect? The spatial organization of pathogens and the gut microbiota in disease

The human gut hosts a dense and diverse microbial community, spatially organized in multiple scales of structure. Here, we review how microbial organization differs between health and disease. We describe how changes in spatial organization may induce alterations in gut homeostasis, concluding with a future outlook to reveal causality.     

Bioconversion of Raw Glycerol Generated from the Synthesis of Biodiesel by Different Oleaginous Yeasts: Lipid Content and Fatty Acid Profile of Biomass

In this work, 12 different yeast strains were evaluated to gauge their ability to accumulate lipids using raw glycerol as the main carbon source. Lipomyces lipofer NRRL Y-1155 stood out above the other strains, achieving 9.48 g/l biomass, 57.64 % lipid content and 5.46 g/l lipid production. The fatty acid profile was similar to vegetable oils commonly used in the synthesis of biodiesel, with the predominance of polyunsaturated acids, especially linoleic acid, reaching 68.3 % for Rhodotorula glutinis NRRL YB-252. The occurrence of palmitic acid (39.3 % for Lipomyces starkeyi NRRL Y-11557) was also notable. Thus, yeast biomass with high lipid content can be a sustainable and renewable alternative as a raw material for the biodiesel industry.     

Aerobic microbial activity in fresh and aged bottom ashes from municipal solid waste incineration (MSWI)

Although mostly mineral, municipal solid waste incineration (MSWI) bottom ashes also contain organic matter that may support heterogeneous microbial activities. The objective of the present study was to evaluate the potential influence of such activities on the physico-chemical properties of the waste with respect to the release of contaminants into water. Fresh and aged MSWI bottom ashes originating from the same incineration plant were studied. Respirometry assays were carried out under various experimental conditions, where the microbial flora was quantitatively and qualitatively analyzed before and after the incubations. The leaching behavior of the waste was studied before and after the incubations to determine the effects of microbial activities.Relatively high O₂ consumption and CO₂ production were observed during incubation, particularly with the fresh waste which contained more organic matter and was less carbonated than the aged one. Cell counts and DGGE molecular profiles indicated the presence of an abundant and diversified microbial biomass in both aged and fresh waste. Incubations resulted in a reduction of the dissolved fraction of organic carbon in the leaching tests and a modification of the leaching patterns of many metallic species (Al, Cr, Cu, Fe, Pb and Zn). This influence on the leaching behavior was particularly significant with the fresh waste. It was mostly explained by the pH decrease due to the carbonation of the bottom ash resulting from the CO₂ generated by the microbial respiration.     

A method to distinguish microbial acclimation from reduced growth rates in perturbed ecosystems

Abstract Predicting variations in microbial growth rates (μ) in Nature requires a method that will detect departures from optimal μ, determine the time scale at sub-optimal μ, and measure the restoration or reversibility toward optimal μ. Isotopic flux measurements are equivocal because of uncertainties in their relationship to μ, particularly in non-steady state condictions. After perturbing a natural microbial community and a clone of the phytoplankter Selenastrum capricornutum with two different toxicants, we examined the kinetics of the adenylate energy charge, and followed changes in biomass over time with the total adenylate and chlorophyll a concentrations. We determined that exposure to cadmium resulted in a reduction in μ; reversible within a short time, whereas exposure to the industrial effluent caused an exponential loss of adenylates and complete inhibition of growth. Upon perturbing a microbiol community, the study of adenylate energy charge kinetics detects departures from optimal μ, measures their duration and reversibility.     

An investigation of hydroethidine as a fluorescent vital stain for prokaryotes

Abstract Hydroethidine (HE), manufactured by the chemical reduction of ethidium bromide (EB), was found to be decomposed to a bright red-fluorescent product by a range of microorganisms. Therefore, HE seemed to have potential as a fluorescent vital stain for microorganisms. However, inhibited or killed bacterial cultures still fluoresced red. Short periods (2–4 min) of excitation of sterile solutions of HE with a UV light yielded an orange/red product. Thus, HE seems to be decomposed biologically by a number of microorganisms but also abiotically by UV light-mediated process to red fluorescent material. These observations suggest that the oxidation of HE has only limited potential for assessing microbial activity.     

Temperature control of nitrogen fixation in Klebsiella pneumoniae

At growth temperatures above 37°C, Klebsiella pneumoniae does not grow in a medium containing N₂ or NO ₃ ^- as nitrogen sources. However, both the growth in the presence of other nitrogen sources as well as the in vitro nitrogenase activity are not affected at this temperature. The inability to fix N₂ at high temperature is due to the failure of the cells to synthesize nitrogenase and other nitrogen fixation (nif) gene encoded proteins. When cells grown under nitrogen fixing conditions at 30°C were shifted to 39°C, there was a rapid decrease of the rate of de novo biosynthesis of nitrogenase (component 1), nitrogenase reductase (component 2), and the nifJ gene product. There was no degradation of nitrogenase at the elevated temperature since preformed enzyme remained stable over a period of at least 3 h at 39°C. Thus, temperature seems to represent a third control system, besides NH ₄ ⁺ and O₂, governing the expression of nif genes of K. pneumoniae.     

Analysis of low-molecular mass products from biosolubilized coal

Abstract A relatively simple, rapid sample preparation method has been developed for analysis of low-molecular mass compounds present in soluble coal products generated by microbial coal solubilizing agents. Acidification of the sample followed by direct extraction into hexanes is coupled with gas chromatography/mass spectrometry analysis for characterization of the soluble coal products. Characterization of the products can contribute to a more complete understanding of the solubilization processes involved, provide further information as to the structure of coal and identify products of potential commercial value.     

Host re-identification of cyanophage PP and its implications for host range and specificity

Dear Editor, In this study,we re-identified the hosts of cyanophage PP.Twenty-three candidate algal strains were tested,and the results indicated that seven strains belonging to Plectonema and Phormidium are the hosts of cyanophage PP,including two previously reported filamentous cyanobacteria,Plectonema boryanum and Phormidium foveolarum (Zhao et al.2002).However,several species or strains within the two genera were found not to be hosts of cyanophage PP,implying that the host range is relatively specific.     

生防真菌耐旱特性的生理生化基础及其利用

丝孢类生防真菌常需满足高湿度条件才能萌发和侵染害虫,已成为广泛应用真菌杀虫剂控制害虫的重要限制因素,适当的剂型化技术在一定程度上能够降低菌剂对环境湿度的依赖性,但生防真菌侵染体本身的耐旱性对菌剂的环境适应性起决定性作用,文中回顾和评述了近20多年来国际上生防真菌耐旱性研究与利用的主要进展,分析和总结了生防真菌耐旱性的生理生化基础及其水活度调控原理,讨论了提高低分子多元醇及海藻糖等生物学相容溶质在侵染体内积聚而增强菌剂耐旱性的可能途径．认为认识决定耐旱性的胞内相容溶质积累的分子生物学基础及其调控机理,探索建立从生理生化水平上最大限度地增强生防菌剂耐旱性的新工艺,是今后生防真菌基础与应用研究的重要方向。