微生物能源的转化效率和经济可行性研究

生物质能源在中国,尤其是农村地区是一种十分重要的能源,然而,目前和将来油气资源的缺乏不仅影响国民经济的发展,而且危及能源安全。估算了4种最具应用前景的微生物能源包括微生物柴油,生物乙醇,氢气和沼气,并讨论了经济可行性及使用前景。其诣在帮助发展将生物质转化为燃料的技术,而此项技术对中国经济的发展具有重要的意义。     

Correlation between cell composition and carbon conversion efficiency in microbial growth: a theoretical study

Summary As the macromolecular composition of microorganisms varies during their life cycle it was asked whether, and to what extent such changes exert any influence on substrate consumption, i.e. growth yield and carbon conversion efficiency, respectively. This question was dealt with in a theoretical study by use of the Y _APT ^max -concept. The growth substrates considered were methanol, acetate and glucose; the latter was assumed to be assimilated via both the glycolytic and the oxidative hexosemonophosphate pathway. Five fictitious biomasses were used which were altered in their proportion of polysaccharides, proteins, lipids, RNA and DNA. As a result, only small variations in the individual biomass formulae were obtained. On the basis of the energy balances for the syntheses of all cell constituents it was found that variations in the macromolecular composition of microbial biomass have only a slight effect on carbon conversion efficiency, amounting to maximally 3%. From the material balances it could be calculated that the upper, solely metabolism-determined limit of carbon conversion efficiency is 85% for substrates assimilated glycolytically via phosphoglycerate; for gluconeogenetic substrates, the upper limit was 75%. These limits are essentially determined by carbon loss on the way to amino acid syntheses.Abbreviations Ac acetate - CCE carbon conversion efficiency (%) - EMP Embden-Meyerhof-Parnas (glycolytic) pathway - Gluc glucose - HMP oxidative hexosemonophosphate pathway - m _e maintenance coefficient (mmol g^-1 h^-1) - MeOH methanol - PGA phosphoglycerate, Y, growth yield (g dry weight per g substrate) - Y _ATP growth yield (g dry weight per mole ATP) - specific growth rate (h^-1)     

Comparison of methods to investigate microbial populations in soils under different agricultural management

As water is a source of nosocomial infections in hospitals, the presence of fastidious Gram-negative bacteria in water samples taken in a university hospital was investigated. Water samples were inoculated onto agar plates and into amoebal microplates for co-culture. Sixty-eight alpha proteobacteria isolates were obtained and characterized using phenotypic methods and 16S rRNA gene sequence comparison. The latter approach divided the strains into seven clusters. Of these, one corresponded to previously recognized Afipia felis and it is likely that six were closely related new species. As these bacteria are fastidious and can not be cultivated on standard microbiological media, their possible role in hospital-acquired human infections should be investigated.     

The conversion of phosphoserine residues to selenocysteine residues on an opal suppressor tRNA and casein

This study has been undertaken in order to elucidate the mechanisms of incorporation of Se into glutathione peroxidase (GSHPx), in which selenocysteine corresponds to the opal termination codon UGA on the mRNA. We studied the above mechanisms using an opal suppressor tRNA, prepared from bovine liver, and casein as a model protein for the GSHPx apo-enzyme which might contain phosphoserine. The results showed that opal suppressor tRNA did not accept selenocysteine (lower than 0.1 mmol/mol) under the standard conditions. A trace amount of phosphoseryl-tRNA was converted to selenocysteyl-tRNA by incubation with H2Se and some enzymes. Meanwhile, a number of phosphoserine residues in casein were converted to selenocysteine residues by incubation with H2Se and enzymes. These results suggest that opal suppressor tRNA plays a role in synthesizing GSHPx via co- and/or post-translational mechanisms.     

Enhancement of methane production from cassava residues by biological pretreatment using a constructed microbial consortium

In the study, a stable thermophilic microbial consortium with high cellulose-degradation ability was successfully constructed. That several species of microbes coexisted in this consortium was proved by DGGE (denaturing gradient gel electrophoresis) and sequence analysis. The cooperation and symbiosis of these microbes in this consortium enhanced their cellulose-degradation ability. The pretreatment of cassava residues mixing with distillery wastewater prior to anaerobic digestion was investigated by using this microbial consortium as inoculums in batch bioreactors at 55 °C. The experimental results showed that the maximum methane yield (259.46 mL/g-VS) of cassava residues was obtained through 12 h of pretreatment by this microbial consortium, which was 96.63% higher than the control (131.95 mL/g-VS). In addition, it was also found that the maximum methane yield is obtained when the highest filter paper cellulase (FPase), carboxymethyl cellulase (CMCase) and xylanase activity and soluble COD (sCOD) are produced.     

Quantitative isolation of microbial DNA from the different types of soils of natural and agricultural ecosystems

A novel procedure was developed for direct quantitative isolation of microbial DNA from soil. This technique was used to evaluate microbial DNA pools in soils of contrasting types (chernozems and brown forest soils) under different anthropogenic loads. A strong correlation was found between microbial biomass and DNA contents in soils of different types (R2 = 0.799). The ratio of soil CO2 emission rate to the amount of extractable DNA in the soil was shown to reflect physiological state of the soil microbial community; this ratio can be used as an ecophysiological parameter similarly to the metabolic quotient qCO2.     

微重力环境下的细菌生物学效应

本文主要根据国内外微重力环境下细菌生物学效应的研究文献,从细菌生长繁殖、抗生素敏感性、毒力变化、新陈代谢等方面进行总结,并概述了微重力环境改变细菌生物学性状的作用机制,展望了微重力环境细菌生物学技术的未来发展。     

X-ray absorption spectroscopy and its application in biological,agricultural and environmental research

X-ray absorption spectroscopy is aspectroscopic in situ technique whichcombines the high penetration strength inherentto X-rays with the advantages of local probetechniques, such as no need for long rangeorder and the ability to obtain information onselected sites of a given sample only.Consequently, this technique is applicable to abroad variety of scientific questions,including many applications in biological,agricultural and environmental sciences. Thefirst part of this review provides anintroduction to the method, whose applicationto a broad variety of problems is discussed indetail, especially XAS of sulfur in biologicalsystems. In the second part new ideas forfurther experiments using this versatile methodare presented.     

The effect of different N substrates on biological N2O production from forest and agricultural light textured soils

N₂O emissions from two slightly alkaline sandy soils, from arable land and a woodland, were determined in a laboratory experiment in which the soils were incubated with different sources of nitrogen, with or without glucose, and with 0, 1 and 100 mL C₂H₂ L^-1. Large differences in the rate of N₂O production were observed between the two soils and between the different N treatments. The arable soil showed very low N₂O emissions derived from reduced forms of N as compared with the N₂O which was produced when the soil was provided with NO ₂ ^- or NO ₃ ^- and a C source, suggesting a very active denitrifier population. In contrast, the woodland soil showed a very low denitrification activity and a much higher N₂O production derived from the oxidation of NH ₄ ⁺ and reduction of NO ₂ ^- by some processes probably mediated by autotrophic or heterotrophic nitrifiers or dissimilatory NO ₂ ^- reducers. In both soils, the highest N₂O emissions were induced by NO ₂ ^- addition. Those emissions were demonstrated to have a biological origin, as no significant N₂O emissions were measured when the soil was autoclaved.     

The drought environment: physical, biological and agricultural perspectives

'Drought' has many meanings in relation to crop production. These range from: statistical (say, the lowest decile of annual rainfall) to a meteorologist; through yield being limited by too little water to an agronomist; to sudden severe water deficits to many molecular biologists. To a farmer, the corresponding management issues, respectively, are risk management (how best to manage a meteorologically drought-prone farm over several years), how best to match cultivar and agronomic operations to the developing growing season, and how best to minimize possible major damage to (say) floral fertility induced by severe water deficits during flowering. All these definitions and the issues they imply are relevant to improving crop production when water is limiting. How can scientists best help? The answers depend on the scales (temporal and spatial) being addressed. Agronomists and breeders, interacting, can help improve components of seasonal water balance in the field, for example, minimizing evaporative losses from the soil surface by better matching the development of a crop to its environment. Physiologists, biochemists, and molecular biologists can help by identifying ways of improving the competence of particular organs. A promising target is floral infertility resulting from water deficits, which results from lesions in tissue, and cellular and molecular processes. Choosing problems whose solutions will have implications in the field and be attractive to farmers requires knowledge of what is important in the field.     

Dynamics of biological and chemical parameters during vermicomposting of solid textile mill sludge mixed with cow dung and agricultural residues

In India, thousands of tons of textile mill sludge are produced every year. We studied the ability of epigeic earthworm Eisenia foetida to transform textile mill sludge mixed with cow dung and/or agricultural residues into value added product, i.e., vermicompost. The growth, maturation, mortality, cocoon production, hatching success and the number of hatchlings were monitored in a range of different feed mixtures for 11 weeks in the laboratory under controlled environmental conditions. The maximum growth and reproduction was obtained in 100% cow dung, but worms grew and reproduced favorably in 80% cow dung + 20% solid textile mill sludge and 70% cow dung + 30% solid textile mill sludge also. Addition of agricultural residues had adverse effects on growth and reproduction of worms. Vermicomposting resulted in significant reduction in C:N ratio and increase in TKN, TP, TK and TCa after 77 days of worm activity in all the feeds. Vermicomposting can be an alternate technology for the management of textile mill sludge if mixed with cow dung in appropriate quantities.     

Isolation and identification of xylitol-producing yeasts from agricultural residues

Selected yeast strains isolated from corn silage and viticulture residues were screened for their capacities to convert D-xylose into xylitol A conventional TLC was adapted for easy determination of xylose and xylitol in the culture supernatant solutions. This technique is suitable for the first steps of a screening program to select xylitol-producing yeasts from natural environments. Candida tropicalis ASM III (NRRL Y-27290), isolated from corn silage, appears to be a promising strain for xylitol production with a high yield (0.88 g xylitol per g of xylose consumed).     

小鳞Jian的维持日粮与转换效率

1998年8月在一个养虾场蓄水池利用网箱进行了小鳞Jian维持日粮与转换效率的研究,小鳞jian生长率（GR）与日粮（DR）的关系可表示为GR＝140．37DR－24．03;食物转换效率和能量转换效率分别为13．96％和16．12％,从生长率和特定生长率计算的小鳞Jian维持日粮分别为体重的17．12％,和20．39％,表明从生长率和特定生长率计算维持日粮可能会导致不同的结果,当日粮水平低于3．30％时,小鳞Jian生长表现异常,意味着它可能利用了网采浮游动物以外的其它食物源。     

The variability of soil microbial community composition of different types of tidal wetland in Chongming Dongtan and its effect on soil microbial respiration

Previous studies have shown that the soil enzyme activity and microbial respiration intensities varied in two different types of tidal wetland in Chongming Dongtan, the first a sandy soil in a scouring bank with Phragmites australis and the second a saline-alkali clay soil in silting bank with P. australis/Spartina alterniflora/Scirpus mariqueter, resulting in different organic carbon reservation capabilities; however, their microbial biomass did not differ significantly. To clarify the microbial mechanism that explains the variability of soil respiration among different wetland areas, the community structure and abundance of soil microorganisms in different types of wetland were investigated using denaturing gradient gel electrophoresis (DGGE) plus real-time quantitative polymerase chain reaction (PCR) technologies, and the relationship between soil environmental factors and the microbial community structure and the soil respiration intensity was elucidated. The results revealed that the soil microbial diversity and community structure differed between the two typical wetland areas. The common population was uncultured bacterium in both areas, and the most abundant community was α-, β-, γ-Proteobacteria, which play an important role in the cycling of carbon in soil. However, the abundance of α-Proteobacteria in Area A was 18.2% of that in Area B (P <0.05), while the β-Proteobacteria in Area A was 3.23 times higher than that in Area B (P <0.05). In addition, one cellulose-degrading bacteria, uncultured Bacilli, was detected in Area A. PCA (Principal component analysis) revealed that γ-Proteobacteria and β-Proteobacteria had the greatest impact on soil respiration intensity. Both soil water content and salinity depressed the propagation of β-Proteobacteria. Considering the similar microbial biomass and abundance of γ-Proteobacteria between the two areas, the lower level of β-Proteobacteria, uncultured Bacilli bacterium in Area B might be important factors involved in the lower soil respiration, and hence the higher soil organic carbon reservation capability in Area B.     

Soil microbial diversity and the sustainability of agricultural soils

Many world ecosystems are in various states of decline evidenced by erosion, low productivity, and poor water quality caused by forest clearing, intensive agricultural production, and continued use of land resources for purposes that are not sustainable. The biological diversity of these systems is being altered. Little research has been conducted to quantify the beneficial relationships between microbial diversity, soil and plant quality, and ecosystem sustainability. Ecosystem functioning is governed largely by soil microbial dynamics. Differences in microbial properties and activities of soils have been reported but are restricted to general ecological enumeration methods or activity levels, which are limited in their ability to describe a particular ecosystem. Microbial populations and their responses to stresses have been traditionally studied at the process level, in terms of total numbers of microorganisms, biomass, respiration rates, and enzyme activities, with little attention being paid to responses at the community or the organismal levels. These process level measurements, although critical to understanding the ecosystem, may be insensitive to community level changes due to the redundancy of these functions. As microbial communities comprise complex interactions between diverse organisms, they should be studied as such, and not as a black box into which inputs are entered and outputs are received at measured rates. Microbial communities and their processes need to be examined in relation to not only the individuals that comprise the community, but the effect of perturbations or environmental stresses on those communities.     

Determination of residues of enrofloxacin and its metabolite ciprofloxacin in biological materials by capillary electrophoresis

A method for the analysis of enrofloxacin and ciprofloxacin in chicken muscle using marbofloxacin as internal standard is proposed. Clean-up and pre-concentration of the samples are effected by solid-phase extraction and determination is carried out by capillary electrophoresis using a photodiode array detector. The calibration graphs are linear for enrofloxacin and ciprofloxacin from 10 to 300 μg/kg. The method recoveries for enrofloxacin and ciprofloxacin are 74 and 54%, respectively. The limit of detection for the two compounds is lower than 25 μg/kg, which allows the detection of positive muscle samples at the required maximum residue limits.