An integrated approach for assessing the bioreceptivity of glazed tiles to phototrophic microorganisms

A laboratory-based methodology was designed to assess the bioreceptivity of glazed tiles. The experimental set-up consisted of multiple steps: manufacturing of pristine and artificially aged glazed tiles, enrichment of phototrophic microorganisms, inoculation of phototrophs on glazed tiles, incubation under optimal conditions and quantification of biomass. In addition, tile intrinsic properties were assessed to determine which material properties contributed to tile bioreceptivity. Biofilm growth and biomass were appraised by digital image analysis, colorimetry and chlorophyll a analysis. SEM, micro-Raman and micro-particle induced X-ray emission analyses were carried out to investigate the biodeteriorating potential of phototrophic microorganisms on the glazed tiles. This practical and multidisciplinary approach showed that the accelerated colonization conditions allowed different types of tile bioreceptivity to be distinguished and to be related to precise characteristics of the material. Aged tiles showed higher bioreceptivity than pristine tiles due to their higher capillarity and permeability. Moreover, biophysical deterioration caused by chasmoendolithic growth was observed on colonized tile surfaces.     

A process for microbial hydrocarbon synthesis: Overproduction of fatty acids in Escherichia coli and catalytic conversion to alkanes

The development of renewable alternatives to diesel and jet fuels is highly desirable for the heavy transportation sector, and would offer benefits over the production and use of short‐chain alcohols for personal transportation. Here, we report the development of a metabolically engineered strain of Escherichia coli that overproduces medium‐chain length fatty acids via three basic modifications: elimination of β‐oxidation, overexpression of the four subunits of acetyl‐CoA carboxylase, and expression of a plant acyl–acyl carrier protein (ACP) thioesterase from Umbellularia californica (BTE). The expression level of BTE was optimized by comparing fatty acid production from strains harboring BTE on plasmids with four different copy numbers. Expression of BTE from low copy number plasmids resulted in the highest fatty acid production. Up to a seven‐fold increase in total fatty acid production was observed in engineered strains over a negative control strain (lacking β‐oxidation), with a composition dominated by C₁₂ and C₁₄ saturated and unsaturated fatty acids. Next, a strategy for producing undecane via a combination of biotechnology and heterogeneous catalysis is demonstrated. Fatty acids were extracted from a culture of an overproducing strain into an alkane phase and fed to a Pd/C plug flow reactor, where the extracted fatty acids were decarboxylated into saturated alkanes. The result is an enriched alkane stream that can be recycled for continuous extractions. Complete conversion of C₁₂ fatty acids extracted from culture to alkanes has been demonstrated yielding a concentration of 0.44 g L^?1 (culture volume) undecane. Biotechnol. Bioeng. 2010;106: 193–202. © 2010 Wiley Periodicals, Inc.     

Alpha粒子和柴油机尾气颗粒提取物共同处理哺乳动物细胞的协同毒性作用

为研究两种有害环境因子同时作用对人类健康的影响,以alpha粒子和柴油机尾气颗粒提取物(d iese lparticu late extract,DPE)共同处理皮肤成纤维细胞(AG1522)为实验模型,对细胞毒性、遗传毒性进行研究。实验发现和未处理的对照组相比,1 cGy alpha粒子和20μg/mL DPE处理24 h,共同作用于细胞能够导致细胞活力下降40%左右,微核形成率上升2倍多;而1 cGy alpha粒子单独辐照时细胞活力下降14.19%,微核形成率上升了36.84%,20μg/mL DPE单独处理24 h时细胞活力下降17.29%,微核形成率上升了73.68%。实验结果表明:这两种环境因子共同作用于哺乳动物细胞时,对于细胞的毒性不是简单的叠加,而是表现出一种协同效应。     

Effects of diesel particles on the control of intracellular mycobacterial growth by human macrophages in vitro

Changes that may modify the capacity of macrophages to control mycobacterial growth could favour the reactivation of bacillary proliferation within protective granulomas developed in response to mycobacterial infection. There is increasing evidence that diesel exhaust particles (DEPs) could suppress some macrophage functions, but it is not known whether DEPs may alter macrophage mycobactericidal activity. The aim of this study was to assess the effect of DEPs on the mycobactericidal activity of human mononuclear phagocytes in vitro. Human monocytes from healthy donors were cultured for 3 days in the presence or absence of DEPs or carbon black particles (CBPs), and then infected with a Mycobacterium bovis bacillus Calmette-Guérin reporter strain expressing luciferase activity. DEPs were rapidly internalized by monocyte-derived macrophages without cytotoxic effect. Mycobactericidal activity of cells exposed to DEPs was not different from that of cells cultured in their absence or in the presence of CBPs. Although our study was restricted to the mycobactericidal activity of human macrophages in vitro, the results indicate that DEPs do not directly influence the first line of defence against microorganisms. Whether exposure to DEPs influences the adaptive immune response against mycobacterial infections remains to be determined.     

Role of Sophorolipid Biosurfactant in Degradation of Diesel Oil by Candida tropicalis

The yeast Candida tropicalis, isolated from petroleum-contaminated soil in India, was found to be the potent producer of biosurfactant in mineral salt media containing diesel oil as the carbon source and found to be an efficient degrader of diesel oil (98%) over a period of 10 days. The crude biosurfactant decreased the surface tension of cell-free broth, 78 to 30 mN/m, with a large oil displacement area and highly positive drop collapse test. The crude biosurfactant was purified using silica gel column chromatography followed by dialysis. With the use of Fourier transform infrared (FT-IR) spectroscopy, in combination with gas chromatography–mass spectrometry (GC-MS) analysis, chemical structures of the purified biosurfactant was identified as sophorolipid species. Involvement of biosurfactant in physiological mechanism of diesel adsorption on yeast cell surface was characterized based on zeta potential. When diesel oil was emulsified with biosurfactant, the surface charge of the diesel was modified, resulting in more adsorption of diesel on yeast cell surface. Biosurfactant production by yeast species was monitored using scanning electron microscopy (SEM) analysis and found that yeast species could form thick mat of mucilaginous biosurfactant that could interconnect the individual cells. Uptake of diesel oil by C. tropicalis was elucidated through transmission electron microscopy (TEM) analysis. Interestingly, it was observed that internalization of diesel oil droplet was taking place, suggesting a mechanism similar in appearance to active pinocytosis.     

2种表面活性物质对70%嘧磺隆WP防治薇甘菊的增效作用

【背景】薇甘菊是最具危害性的世界性杂草之一,目前已入侵我国香港、广东、海南、台湾、云南等地,而嘧磺隆是防治薇甘菊的一种高效药剂。【方法】采用室内生物测定和田间喷雾法,研究了商用药剂嘧磺隆与洗衣粉或柴油混合使用,对薇甘菊根、茎、叶片的杀灭效果及对后期残留茎干萌发率和种子萌芽率的抑制作用。【结果】嘧磺隆单独处理28d后,薇甘菊叶片、茎和根的死亡率分别为86％、92％和84％;而与洗衣粉混合处理后,死亡率分别升高至98．33％、97．67％和89．67％;与柴油混合使用后,死亡率分别升高至92．33％、95．33％和98．33％。经嘧磺隆单独处理后的薇甘菊后期茎干萌发率为9．67％;与洗衣粉、柴油混合使用后,萌发率分别降低至6％、5．33％。经嘧磺隆单独处理后,薇甘菊种子的萌芽率为44．67％;而与洗衣粉、柴油混合使用后,种子萌芽率分别降至28．67％、25．33％。【结论与意义】嘧磺隆与洗衣粉或柴油混合使用,对薇甘菊组织的杀灭效果及对后期茎干萌发率和种子萌芽率的抑制作用均优于嘧磺隆单独使用。本研究可以为薇甘菊的防控技术开发提供参考。     

Characteristics and role of the exocellular polysaccharides produced by five cyanobacteria isolated from phototrophic biofilms growing on stone monuments

Three coccoid and two filamentous cyanobacterial strains were isolated from phototrophic biofilms exposed to intense solar radiation on lithic surfaces of the Parasurameswar Temple and Khandagiri caves, located in Orissa State, India. Based on to their morphological features, the three coccoid strains were assigned to the genera Gloeocapsosis and Gloeocapsa, while the two filamentous strains were assigned to the genera Leptolyngbya and Plectonema. Eleven to 12 neutral and acidic sugars were detected in the slime secreted by the five strains. The secretions showed a high affinity for bivalent metal cations, suggesting their ability to actively contribute to weakening the mineral substrata. The secretion of protective pigments in the polysaccharide layers, namely mycosporine amino acid-like substances (MAAs) and scytonemins, under exposure to UV radiation showed how the acclimation response contributes to the persistence of cyanobacteria on exposed lithoid surfaces in tropical areas.     

The impact of culture medium on the development and physiology of biofilms of Pseudomonas fluorescens formed on polyurethane paint

Microbial biofilms cause the deterioration of polymeric coatings such as polyurethanes (PUs). In many cases, microbes have been shown to use the PU as a nutrient source. The interaction between biofilms and nutritive substrata is complex, since both the medium and the substratum can provide nutrients that affect biofilm formation and biodeterioration. Historically, studies of PU biodeterioration have monitored the planktonic cells in the medium surrounding the material, not the biofilm. This study monitored planktonic and biofilm cell counts, and biofilm morphology, in long-term growth experiments conducted with Pseudomonas fluorescens under different nutrient conditions. Nutrients affected planktonic and biofilm cell numbers differently, and neither was representative of the system as a whole. Microscopic examination of the biofilm revealed the presence of intracellular storage granules in biofilms grown in M9 but not yeast extract salts medium. These granules are indicative of nutrient limitation and/or entry into stationary phase, which may impact the biodegradative capability of the biofilm.     

Inhibitory effects of diesel exhaust components and flavonoids on 20α-hydroxysteroid dehydrogenase activity in mouse tissues

The inhibitory effects of diesel exhaust components and flavonoids on 20α-hydroxysteroid dehydrogenase (20α-HSD) activity were examined in cytosolic fractions from the liver, kidney and lung of male mice. 9,10-Phenanthrenequinone (9,10-PQ) and 1,2-naphthoquinone (1,2-NQ), which are contained in diesel exhaust particles (DEPs), potently inhibited 20α-HSD activity in liver cytosol. 9,10-PQ also inhibited the enzyme activity in lung cytosol. However, 20α-HSD activity in kidney cytosol was little inhibited by 9,10-PQ or 1,2-NQ. Flavonoids such as quercetin, fisetin and kaempferol exhibited high inhibitory potencies for 20α-HSD activity in liver cytosol, whereas these flavonoids were poor inhibitors for the enzyme activity in kidney cytosol. It is likely that several diesel exhaust components and flavonoids augment the signaling of progesterone in the liver cells, by potently inhibiting 20α-HSD activity in mouse liver cytosol. The possibility that there are distinct enzymes catalyzing 20α-HSD activity in the non-reproductive tissues of male mice is also discussed.     

Bioconversion of natural gas to liquid fuel: Opportunities and challenges

Natural gas is a mixture of low molecular weight hydrocarbon gases that can be generated from either fossil or anthropogenic resources. Although natural gas is used as a transportation fuel, constraints in storage, relatively low energy content (MJ/L), and delivery have limited widespread adoption. Advanced utilization of natural gas has been explored for biofuel production by microorganisms. In recent years, the aerobic bioconversion of natural gas (or primarily the methane content of natural gas) into liquid fuels (Bio-GTL) by biocatalysts (methanotrophs) has gained increasing attention as a promising alternative for drop-in biofuel production. Methanotrophic bacteria are capable of converting methane into microbial lipids, which can in turn be converted into renewable diesel via a hydrotreating process. In this paper, biodiversity, catalytic properties and key enzymes and pathways of these microbes are summarized. Bioprocess technologies are discussed based upon existing literature, including cultivation conditions, fermentation modes, bioreactor design, and lipid extraction and upgrading. This review also outlines the potential of Bio-GTL using methane as an alternative carbon source as well as the major challenges and future research needs of microbial lipid accumulation derived from methane, key performance index, and techno-economic analysis. An analysis of raw material costs suggests that methane-derived diesel fuel has the potential to be competitive with petroleum-derived diesel.