ICL、ICDH、ODH和GDH酶与L-谷氨酸的合成

通过对对数生长期细胞的异柠檬酸裂解酶（ICL）、异柠檬酸脱氢酶（ICDH）、α-酮戊二酸脱氢酶（ODH）和谷氨酸脱氢酶（GDH）的分析以及对细胞L-谷氨酸产生量和发酵残糖的综合分析,发现由于乙醛酸循环关键酶ICL的缺失,L-谷氨酸产生量大幅下降,说明乙醛酸循环是谷氨酸棒杆菌中的主要回补途径,L-谷氨酸合成需要乙醛酸循环。在保证乙醛酸循环回补功能的前提下,提高ICDH活性,减弱ODH活性,有利于L-谷氨酸的合成。     

小麦烘干种子活力及其与脱氢酶活性的相关性研究

[目的]探讨小麦烘干种子活力与其脱氢酶活性的相关性。[方法]以5个小麦品种(系)为试材,将新收小麦种子烘干,采用2种贮藏方式下贮藏1年,通过幼苗生长测定小麦烘干种子活力,采用氯化三苯基四氮唑法(TTC法)测定小麦种子脱氢酶活性。[结果](42±1)℃烘干对小麦新种子的发芽势、发芽率及幼苗生长无不良影响,室温密闭贮藏和低温(5～8℃)密闭贮藏2种贮藏方式的小麦烘干种子具有较高的发芽力,其发芽势、发芽率的差异不显著。不论是新种子还是在2种贮藏方式下贮藏1年的陈种子,小麦烘干种子的活力指数与其脱氢酶活性均呈显著正相关,苗干重、发芽势、发芽率、发芽指数与脱氢酶活性均呈正相关。[结论]脱氢酶活性可作为评定小麦烘干种子活力的指标之一。     

Toxicity interaction of metals (Ag, Cu, Hg, Zn) to urease and dehydrogenase activities in soils

A study of the individual and mixture toxicities of the trace metals Ag, Cu, Hg, Zn to the soil enzymes dehydrogenase and urease was undertaken. An agricultural soil and a sandy forest soil were spiked with metal salts, individually and in combinations. The anion additions to the various treatments and controls were normalized for added anions using Ca salts. The soils were then left to equilibrate and leached to reduce the excess metals and anions. Total and dissolved metal concentrations were measured concurrently in order to consider the effect of soil chemistry on the enzyme activities. Dose-response relationships for total soil metals and soil solution metals were estimated for each metal separately following a log-logistic curve fitting. Ag and Hg were the most efficient metals to reduce soil enzyme activities. The Bliss independence model was used to predict the toxicity of metal combinations. The enzyme responses in relation to the total soil metal combinations were synergistic for the agricultural soil and antagonistic for the forest soil; possibly as a result of a higher organic matter content and higher pH in the latter soil. Enzyme activities expressed in relation to the dissolved metal concentrations were more variable than against the total metal contents and consequently we observed both synergistic and antagonistic interactions.     

Microbial biomass turnover and enzyme activities following the application of farmyard manure to field soils with and without previous long-term applications

Summary We studied the build-up and turnover of microbial biomass following the addition of farmyard manure to an unmanured soil and to soils from a long-term experiment in which different levels of farmyard manure had been applied for the last 23 years. The application of farmyard manure at 15–90 t ha^-1 to previously unmanured soil increased the microbial biomass during the first 3 months of incubation but a gradual decline occurred with further incubation for up to 12 months. Microbial biomass C was positively correlated with soil organic C and ranged from 1.8% to 2.2% of organic C after 12 months of farmyard manure applications. Biomass turnover increased with the application of farmyard manure, ranging from 0.81 to 0.87 year^-1 with various levels of manure. Amendment of soils from the long-term manure experiment with various levels of farmyard manure led to a build-up and decline in biomass C as seen in the unmanured soils, but biomass C was higher in all treatments compared to the corresponding unmanured soil treatments. Biomass turnover was greater compared to the unmanured soil treatments and it decreased with increasing levels of farmyard manure. The average soil respiratory activity increased with increasing levels of farmyard manure, but respiratory activity per unit of biomass C decreased with increasing levels of manure. Enzyme activities were greater in long-term manured soils compared to unmanured soils amended with various levels of manure. There was a significant correlation between biomass C and enzyme activities.     

设施土壤中微生物生物量碳和脱氢酶活性对镉与邻苯二甲酸酯复合污染的响应

为了揭示设施土壤中Cd与PAEs复合污染效应,通过盆栽试验验证了设施土壤中微生物生物量碳含量和脱氢酶活性对Cd-PAEs复合污染的响应。结果表明:移栽后20 d,施加低浓度Cd(≤2.0 mg/kg),可使土壤中微生物生物量碳含量增加,设施和大田土壤中分别增加了42.7%和96.5%。移栽后20 d时,施加PAEs(40,80 mg/kg)使设施土壤微生物生物量碳含量分别降低了56.2%和46.7%;移栽后30 d时,施加PAEs(40,80 mg/kg)使大田土壤微生物生物量碳含量分别降低了39.8%和提高了21.6%。Cd处理使大田土壤脱氢酶活性降低,但并未使设施土壤脱氢酶活性发生显著变化。施加高浓度PAEs(80 mg/kg)使大田土壤的脱氢酶活性提高了33.6%,但却使设施土壤脱氢酶活性降低了40.0%。Cd-PAEs复合效应对土壤微生物生物量碳表现为协同作用,但土壤脱氢酶活性则产生了拮抗作用。     

Interactions between the arbuscular mycorrhizal fungus Glomus intraradices and the plant growth promoting rhizobacteria Paenibacillus polymyxa and P. macerans in the mycorrhizosphere of Cucumis sativus

Interactions between the arbuscular mycorrhizal (AM) fungus Glomus intraradices and bacteria from the genus Paenibacillus (P. macerans and P. polymyxa) were examined in a greenhouse pot experiment with Cucumis sativus with and without organic matter amendment (wheat bran). P. polymyxa markedly suppressed AM fungus root colonization irrespective of wheat bran amendment, whereas P. macerans only suppressed AM fungus root colonization in combination with wheat bran amendment. Dual inoculation with P. macerans and G. intraradices in combination with wheat bran amendment also caused severe plant growth suppression. Inoculation with G. intraradices was associated with increased levels of dehydrogenase activity and available P in the growth substrate suggesting that mycorrhiza formation accelerated the decomposition of organic matter resulting in mobilization of phosphorus. Inoculation with both Paenibacillus species increased all measured microbial fatty acid biomarkers in the cucumber rhizosphere, except for the AM fungus biomarker 16:1ω5, which was reduced, though not significantly. Similarly, inoculation with G. intraradices increased all measured microbial fatty acid biomarkers in the cucumber rhizosphere, except for the Gram-positive bacteria biomarker 15:0 anteiso, which was overall decreased by G. intraradices inoculation. In combination with wheat bran amendment G. intraradices inoculation caused a 39% reduction in the amount of 15:0 anteiso in the treatment with P. polymyxa, suggesting that G. intraradices suppressed P. polymyxa in this treatment. In conclusion, plant growth promoting species of Paenibacillus may have suppressive effects of AM fungi and plant growth, especially in combination with organic matter amendment. The use of an inert plant growth media in the present study allowed us to study rhizosphere microbial interactions in a relative simple substrate with limited interference from other soil biota. However, the results obtained in the present work mainly show potential interactions and should not be directly extrapolated to a soil situation.     

Comparison of chemical and microbiological methods for the characterization of the maturity of composts from contrasting sources

Six composts from different sources (wheat and barley straw; coniferous bark; mixed hop rape and bark; two from household garbage; mixed paper dust and sewage sludge) were characterized by chemical methods, including various forms of N and organic matter fractionation, and by microbiological methods. The dehydrogenase activity, respiration rate, and arginine ammonification were investigated, which represent different aspects of C and N metabolism. Only a few significant correlations were found between different maturity indexes. Dehydrogenase activity was in agreement with the widely accepted humic acid C to fulvic acid C ratio and might therefore be acceptable as a maturity index. Arginine ammonification provided valuable information on the N status in composts; negative values indicated that considerable amounts of easily degradable organic compounds with wide C:N ratios were still present, which would lead to microbial immobilization of soil N after the application of these composts. A combination of dehydrogenase activity and arginine ammonification data led to an unambiguous classification of all composts, and is therefore recommended for further consideration; in contrast, chemical data were contradictory and markedly dependent on the original substrates. The respiration rate, which was closely correlated with the percentage of organic C, did not contribute to the assessment of compost maturity.     

Biological and chemical properties of arable soils affected by long-term organic and inorganic fertilizer applications

 Using soils from field plots in four different arable crop experiments that have received combinations of manure, lime and inorganic N, P and K for up to 20 years, the effects of these fertilizers on soil chemical properties and estimates of soil microbial community size and activity were studied. The soil pH was increased or unaffected by the addition of organic manure plus inorganic fertilizers applied in conjunction with lime, but decreased in the absence of liming. The soil C and N contents were greater for all fertilized treatments compared to the control, yet in all cases the soil samples from fertilized plots had smaller C:N ratios than soil from the unfertilized plots. The soil concentrations of all the other inorganic nutrients measured were greater following fertilizer applications compared with the unfertilized plots, and this effect was most marked for P and K in soils from plots that had received the largest amounts of these nutrients as fertilizers. Both biomass C determined by chloroform fumigation and glucose-induced respiration tended to increase as a result of manure and inorganic fertilizer applications, although soils which received the largest additions of inorganic fertilizers in the absence of lime contained less biomass C than those to which lime had been added. Dehydrogenase activity was lower in soils that had received the largest amounts of fertilizers, and was further decreased in the absence of lime. This suggests that dehydrogenase activity was highly sensitive to the inhibitory effects associated with large fertilizer additions. Potential denitrification and anaerobic respiration determined in one soil were increased by fertilizer application but, as with both the microbial biomass and dehydrogenase activity, there were significant reductions in both N₂O and CO₂ production in soils which received the largest additions of inorganic fertilizers in the absence of lime. In contrast, the size of the denitrifying component of the soil microbial community, as indicated by denitrifying enzyme activity, was unaffected by the absence of lime at the largest rate of inorganic fertilizer applications. The results indicated differences in the composition or function of microbial communities in the soils in response to long-term organic and inorganic fertilization, especially when the soils were not limited. Received: 10 March 1998     

Suitability of dehydrogenase activity assay as an index of soil biological activity

Summary Dehydrogenase activity was studied in typical soils of the Northwest German Lower Plains in order to test some criticisms raised by nannipieri et al. (1990) about methodology. We found that in the same soils with the sampe crop, dehydrogenase activity varies significantly. In the field dehydrogenase activity was dependent on the soil type and not on the cropping system. There is no adequate explanation of these findings. Dehydrogenase activity is a parameter of soil microbiological activity and is influenced by many factors. Either purely accidental the results are or dehydrogenase activity is affected by unknown ecological interactions and by the composition of soil microflora. We conclude that without simultaneous investigations of other microbiological parameters (microbial biomass, ATP levels, enzyme activities, etc.) the measurement of dehydrogenase activity creates confusion and may impede valid ecological comparisons of soils.Dedicated to Prof. H.-P. Blume, Kiel, on the occasion of his 60th birthday     

2,3,5-Triphenyltetrazolium chloride (TTC) as electron acceptor of culturable soil bacteria,fungi and actinomycetes

Dehydrogenase assays based on the reduction of 2,3,5- triphenyltetrazolium chloride (TTC) to the creaming red-coloured formazan (TPF), have been used to determine microbial activity in soil. By spraying TTC on culturable microbial colonies, whose growth was induced by applying glucose, we observed that from 72 to 100% of the bacterial and actinomycetes colonies in different soils were capable of using TTC as an electron acceptor. This percentage decreased to only 5% in the case of fungal colonies.