转Bt基因克螟稻秸杆对淹水土壤细菌群落的影响

在实验室条件下通过秸杆还土试验比较了克螟稻Bt基因表达最高期秸杆和同一时期亲本稻秸杆的添加对淹水土壤可培养厌氧细菌数量和细菌群落组成的影响 .结果表明 ,与亲本对照相比 ,培养初期克螟稻秸杆的添加对淹水土壤厌氧发酵性细菌、产氢产乙酸细菌、反硝化细菌和产甲烷细菌的数量产生了显著性影响 ,但培养后期这种显著性差异基本消失 .PCR 变性梯度凝胶电泳 (DGGE)指纹图谱和主成份分析 (PCA)结果表明 ,两种秸杆处理土壤细菌群落组成在培养的第 3周和第 5周达到显著性差异 ,随着培养时间的延伸 ,两种秸杆处理土壤间细菌群落组成的差异逐渐减小 .到培养的第 1 1周 ,两种秸杆处理土壤间细菌群落组成的差异基本消失 .尽管如此 ,在培养的整个过程中 ,秸杆处理土壤中可培养厌氧性细菌数量和土壤细菌群落的组成均与纯土对照存在显著性差异 .试验结果表明 ,在实验室培养的条件下 ,没有观察到转Bt基因克螟稻秸杆对淹水土壤微生物明显的长期负面影响     

Gas chromatography with atomic absorption detection for the determination of alkyl selenide compounds in the breath of mice after administration of different selenium compounds

Quantitative determination of dimethylselenide and dimethyldiselenide in the breath of mice after addition of different selenium compounds to the drinking water is described. Breath samples are collected with a cryogenic trap and analyzed by gas chromatography with atomic absorption spectrometric detection. Detection limits down to 0.2 ng/100 g body weight are obtained.

The pulmonary excretion of selenium metabolites after oral administration via drinking water or after intraperitoneal injection appears to be negligible. The bioconversion of the different selenium species is discussed.     

Alkylation of metals and the activity of metal‐alkyls†

The biochemical basis for resistance to metal ion toxicity is emerging though it is complicated by the different resistance mechanisms. Several strategies for resistance to toxic metal ions have been identified:

1. The development of energy driven efflux pumps which keep toxic element levels low in the interior of the cell. Such mechanisms have been described for Cd(II) and As(V).

2. Oxidation (e.g. AsO^2‐ to AsO₄ ^3‐) or reduction (e.g. Hg²⁺ to Hg⁰) can enzymatically and intracellularly convert a more toxic form of an element to a less toxic form.

3. The biosynthesis of intracellular polymers which serve as traps for the removal of metal ions from solution such as traps have been described for cadmium, calcium, nickel and copper.

4. The binding of metal ions to cell surfaces.

5. The precipitation of insoluble metal complexes (e.g. metal sulfides and metal oxides) at cell surfaces.

6. Biomethylation and transport through cell‐membranes by diffusion controlled processes.

In this short review I shall discuss the implications of biomethylation as a detoxification mechanism for microorganisms as well as for certain higher organisms.     

Mutagenic activity of transition‐metal complexes: Relation structure‐mutagenic and antibacterial activity for some Pd(II), Pt(II) and Rh(I) complexes†

The inhibitory and mutagenic action of some Pd(II), Pt(II) and Rh(I) complexes towards various bacterial strains has been evaluated, and some correlations have been found between the chemical behaviour of the complexes and their selective biological activity: most of the complexes cause only a DNA damage repaired by the excision repair system. Particularly, the Rh(I) complexes used in this work show selective antibacterial effects on defective but no effect on wild‐type strains.     

Degradation kinetics of terephthalic acid wastewater with the hybrid strains constructed with Phanerochaete chrysosporium

The degradation kinetic parameters in terephthalic acid (TPA) wastewater for the hybrid strains of Fhh and Fhhh obtained through the protoplast fusion of the fungi Phanerochaete chrysosporium (PC) and Saccharomyces cerevisiae Y99, and the native bacteria YZ1 were measured in this research. The highest level of the specific degradation rate for Fhhh and Fhh during 20h reaction were 0.2238 and 0.2163 h^‐1, which were higher than that of their three parental strains and that of the anaerobic bacteria reported. It suggested that the abilities of growth and degradation for Fhh and Fhhh in TPA wastewater were better than their three parental strains. They could create potentials for the purification of TPA wastewater with higher efficiency.     

Presence of hydrocarbon-degrading bacteria in the gills of mussel Mytilus galloprovincialis in a contaminated environment: a mesoscale simulation study

A number of previous studies have shown that the relationships of symbiosis existing between mussels and microorganisms are directly dependent on the environmental conditions. However, little is known about existing relationships between mussels and bacteria in hydrocarbon-impacted marine environments. The aim of this preliminary study is to investigate the presence of oil-degrading bacteria in the mussel Mytilus galloprovincialis during growth in polluted ecosystems. All the experiments were carried out in a mesocosm system designed to simulate chronic pollution and to enable direct exposure of mussels to chemicals. Quantitative (4′,6-diamidino-2-phenylindole, colony-forming units, Most Probable Number) analyses and screening (presence/absence) of metabolic functional genes were performed to analyse bacterial populations inside the gills of mussels exposed and not exposed to hydrocarbons. The data obtained show that the presence of hydrocarbons affected the abundance of bacteria inside the gills of specimens and determines selection for specific (hydrocarbon-degrading) bacteria (i.e. Alcanivorax sp. and Marinobacter sp.). However, is not yet clear whether the presence of such genera of bacteria inside the mussel is due to symbiosis or as a result of filtration.     

Hydrocarbons contamination and microbial degradation in mangrove sediments of the Niger Delta region (Nigeria)

The distribution of aliphatic hydrocarbons and polycyclic aromatic hydrocarbons (PAHs), and their degradability by bacteria in epipelic and benthic sediments from Qua Iboe Estuary mangrove ecosystem and associated creeks were investigated. The research findings revealed that total aliphatic hydrocarbons in sediments ranged from 16.82 mg·kg ^?1 to 210 mg kg ^?1, wheras total PAHs ranged from 6.30 to 35.55 mg·kg ^?1 dry weight of sediment. Low molecular mass (i.e. the 2–3-ring) PAHs were predominant in almost all the sampling points, whereas the higher molecular masses (4-, 5- and 6-ring PAHs) had the lowest concentrations. In general, the sediment samples ES ₂ (39.7%), ES ₃ (24.8%), BS ₁ (46.7%), BS ₂ (49.9%) and BS ₃ (44.2%) showed<50% contributions of Σ combustion–derived PAH (COMP-PAH) concentration to the Σ PAH concentrations, whereas ES ₁ (57%) contained>50% of COMP-PAHs. Our results have also shown that many mangrove bacteria have strong capacity to utilise Qua Iboe Light (QL) crude oil as the sole source of carbon and energy, while lower number of bacterial species including Bacillus sp., Micrococcus sp., Pseudomonas aeruginosa, Alcaligenes sp. and Flavobacterium sp. exhibited detectable PAHs degradability; and as such may serve as efficient degraders of QL crude oil contamination of mangrove ecosystem.     

Microbial Fe(III) Reduction in Acidic Mining Lake Sediments after Addition of an Organic Substrate and Lime

To elucidate the role of Fe(III) reduction in mining lake sediments amended with organic substrates, we performed a large (10 m diameter) enclosure experiment in which sediments were amended with Carbokalk, a waste product from sugar industry containing organic carbon and lime. Fe(III) reduction rates were determined monthly by measuring the accumulation of Fe(II) in the sediments in the field. Fe(III) reduction rates were also determined by incubating sediment samples with synthetic Fe(III) oxyhydroxide under in situ temperature in the laboratory. Sulfate reduction was selectively inhibited in the Fe(III) reduction experiments by addition of sodium molybdate. Sulfate reduction was measured by accumulation of reduced inorganic sulfides in the field and by ³⁵S radiotracer using a core injection technique. Sediment incubation and determination of sulfate reduction rates with radiotracer showed that sulfate reduction and direct microbial Fe(III) reduction occured simultaneously in the upper centimeters of the sediments and that both processes contributed to alkalinity generation. However, Fe(III) reduction was the initial process and rates were at least 3.5 fold higher than sulfate reduction rates. The results indicate that the presence of suitable anions for Fe(II) precipitation as carbonate or sulfide is needed in order to prevent loss of potential alkalinity by Fe(II) diffusion and reoxidation in the water column.     

Sociological dimension in the handling habit and sanitary quality of hand-dug well water from oil-producing area of Nigeria

A previous report showed that the physical and sanitary quality of hand-dug wells from an oil-producing area of Nigeria was poor in spite of the presence of well protective features. The hypothesis that handling habits is associated with the well water quality was therefore, tested. A structured questionnaire with scales for measuring handling habits was administered to 60 female (>18 years) hand-dug well users/owners randomly selected from three towns in the oil-producing area. The respondents’ wells were analysed for coliform bacteria. The findings showed that poor handling habits were the trend (habit score: Mean, 9.23 vs. 20 total available points). Handling habit indicated by scores, significantly negatively correlated (−0.89; P < 0.01) with coliform counts (indicator of poor sanitary quality). While the data collected and discussions with respondents indicated awareness of the risk of drinking well water, widespread skepticism of the potential hazards of non-drinking domestic uses (e.g., cooking, washing of plates, cups, cutleries etc.) was evident. Discontent with some aspects of science was indicated. It is concluded that there is need for social discourse and more public health campaign aimed at transforming skepticism to consent.     

Effects of probiotic bacteria on the bioaccessibility of aflatoxin B1 and ochratoxin A using an in vitro digestion model under fed conditions

In the present study, we aimed at determining the release of aflatoxin B₁ (AFB₁) and ochratoxin A (OTA) from different food products in the gastro-intestinal tract in the absence and presence of probiotics, a possible adsorbent. The average bioaccessibility of AFB₁ and OTA without probiotics was about 90%, and 30%, respectively, depending on several factors, such as food product, contamination level, compound and type of contamination (spiked versus naturally contaminated). The six probiotic bacteria showed varying binding capacity to AFB₁ and OTA depending on the bacterial strain, toxin studied, type of food and contamination level. A reduction to a maximum of 37% and 73% as observed for the bioaccessibility of AFB₁ and OTA in the presence of probiotic bacteria, respectively. This is the first report on the effect of probiotic bacteria on reducing the fraction of mycotoxins available for absorption in the gastrointestinal tract from different food products.