Characterization of a novel microsomal glutathione S-transferase produced by Aspergillus ochraceus TS

Purification and characterization of microsomal glutathione S-transferase produced by Aspergillus ochraceus TS are reported. The isozymes are located in microsomes and were active against 1-chloro-2,4-dinitrobenzene, ethacrynic acid, 1,2-dichloro-4-nitrobenzene, trans-4- phenyl-3-buten-2-one,p-nitrobenzyl chloride and bromosulphophthalein. They were inhibited by N-ethylmaleimide and bromosulphophthalein. The GST isozymes produced by Aspergillus ochraceus TS are indistinguishable in respect of their molecular mass both in native and denatured state. The subunit of the purified protein had an apparent M_r of 11 kDa while molecular mass of the native protein is around 56 kDa. The substrate specificity and pl values of the isozymes were different. The GSTs produced by Aspergillus ochraceus TS fairly share functional properties with mammalian cytosolic isozymes.     

Influence of soil type on the transfer of plasmid RP4p from Pseudomonas fluorescens to introduced recipient and to indigenous bacteria

Abstract Transfer of plasmid RP4p from introduced Pseudomonas fluorescens to a co-introduced recipient strain or to members of the indigenous bacterial population was studied in four different soils of varying texture planted with wheat. Donor and recipient strains showed good survival in the four soils throughout the experiment. The numbers of transconjugants found in donor and recipient experiments in two soils, Ede loamy sand and Löss silt loam were significantly higher in the rhizosphere than in corresponding bulk soil. In the remaining two soils, Montrond and Flevo silt loam, transconjugant numbers were not significantly higher in the rhizosphere than in the bulk soil.
The combined utilization of a specific bacteriophage eliminate the donor strain and the pat sequence as a specific marker to detect RP4p was found to be very efficient in detecting indigenous transconjugants under various environmental conditions. The numbers of indigenous transconjugants were consistently higher in rhizosphere than bull soil. A significant rhizosphere effect on transconjugant numbers of transconjugants were recovered from Flevo and Montrond silt loam; these soils possess characteristics such as clay or organic matter contents which may be favorable to conjugation.     

Metabolism of nitric oxide and nitrous oxide during nitrification and denitrification in soil at different incubation conditions

Abstract NO production and consumption rates as well as N₂O accumulation rates were measured in a loamy cambisol which was incubated under different conditions (i.e. soil moisture content, addition of nitrogen fertilizer and/or glucose, aerobic or anaerobic gas phase). Inhibition of nitrification with acetylene allowed us to distinguish between nitrification and denitrification as sources of NO and N₂O. Under aerobic conditions untreated soil showed very low release of NO and N₂O but high consumption of NO. Fertilization with NH₄⁺ or urea stimulated both NO and N₂O production by nitrification. Addition of glucose at high soil moisture contents led to increased N₂ and N₂O production by denitrification, but not to increased NO production rates. Anaerobic conditions, however, stimulated both NO and N₂O production by denitrification. The production of NO and N₂O was further stimulated at low moisture contents and after addition of glucose or NO₃⁻. Anaerobic consumption of NO by denitrification followed Michaelis-Menten kinetics and was stimulated by addition of glucose and NO₃⁻. Aerobic consumption of NO followed first-order kinetics up to mixing ratios of at least 14 ppmv NO, was inhibited by autoclaving but not by acetylene, and decreased with increasing soil moisture content. The high NO-consumption activity and the effects of soil moisture on the apparent rates of anaerobic and aerobic production and consumption of NO suggest that diffusional constraints have an important influence on the release of NO, and may be a reason for the different behaviour of NO release vs N₂O release.     

Ecophysiology of Aufwuchs-eating cichlids in Lake Tanganyika: niche separation by trophic specialization

Synopsis The Aufwuchs-eating cichlids of Lake Tanganyika show clear trophic differences that are correlated to their morphology, physiology and foraging behaviour. The species are grouped into three categories of relative intestinal length according to their feeding habits. A correlation between the intestinal length and the diet could be demonstrated, ranging from around 2.5 for species ingesting more animal food, to 7.8 for detritivorous and microalgivorous species. The relative intestinal length of domesticTropheus moorii, raised in aquaria was significantly lower than that of wild individuals by a factor of 1.7, demonstrating a wide range of phenotypic adaptability. The activities of trypsin and amylase were at an equal level in four Aufwuchseating species, but the activity of laminarinase of a detritivorous-microalgivorous species (Petrochromis orthognathus) was 2.6 times higher than that of an algivorous species (Tropheus moorii). The laminarinase seems to be an excellent marker enzyme for detritivorous or microalgivorous feeding.     

柴达木盆地荒漠土壤蓝藻群落的初步研究

本文分析了柴达木盆地东部和中部具有代表性地区的丘陵、戈壁和沙丘的蓝藻种类组成、生物量及主要的土壤化学成分;采用了模糊聚类、系统聚类及多元线性回归等方法分析藻类的群落及其与环境因子的关系。共鉴定出21种蓝藻,其中6种为国内首次报道。研究表明:土壤含磷量、总盐量及与粘性和湿度有关的土壤结构是决定柴达木盆地蓝藻群落组成的重要因素。     

Hybrid Bacillus (1-3,1-4)-β-glucanases: engineering thermostable enzymes by construction of hybrid genes

Summary Hybrid (1-3,1-4)--glucanase genes were constructed by extension of overlapping segments of the (1-3,1-4)--glucanase genes from Bacillus amyloliquefaciens and B. macerans generated by the polymerase chain reaction (PCR). Four hybrid genes were expressed in Escherichia coli cells. The mature hybrid enzymes contain a 16, 36, 78, or 152 amino acid N-terminal sequence derived from B. amyloliquefaciens (1-3,1-4)--glucanase followed by a C-terminal segment derived from B. macerans (1-3,1-4)--glucanase. Biochemical characterization of parental and hybrid enzymes shows a significant increase in thermostability of three of the hybrid enzymes when exposed to an acidic environment thus combining two important enzyme characteristics within the same molecule. At pH 4.1, 85%-95% of the initial activity was retained after 1 h at 65° C in contrast to 5% and 0% for the parental enzymes from B. amyloliquefaciens and B. macerans. After 60 min incubation at 70° C, pH 6.0, the parental enzymes retained 5% or less of the initial activity whilst one of the hybrids still exhibited 90% of the initial activity. Of the parental enzymes B. macerans (1-3,1-4)--glucanase had the lower specific activity while the hybrid enzymes exhibited specific activities that were 1.5- to 3-fold higher. These experimental results demonstrate that exchange of homologous gene segments from different species may be a useful technique for obtaining new and improved versions of biologically active proteins.Abbreviations AMY mature form of Bacillus amyloliquefaciens (1-3,1-4)--glucanase; - MAC mature form of B. macerans (1-3,1-4)--glucanase - SUB mature form of B. subtilis (1-3,1-4)--glucanase - H(A16-M), H(A36-M), H(A78-M), H(A107-M), H(A152-M) mature forms of hybrid enzymes having 16, 36, 78, 107, 152 N-terminal amino acids, respectively, derived from AMY with the remaining amino acids derived from MAC     

Capture and allocation of nitrogen byQuercus douglasii seedlings in competition with annual and perennial grasses

Summary The spatial overlap of woody plant root systems and that of annual or perennial grasses promotes competition for soil-derived resources. In this study we examined competition for soil nitrogen between blue oak seedlings and either the annual grassBromus mollis or the perennial grassStipa pulchra under controlled outdoor conditions. Short-term nitrogen competition was quantified by injecting¹⁵N at 30 cm depth in a plane horizontal to oak seedling roots and that of their neighbors, and calculating¹⁵N uptake rates, pool sizes and¹⁵N allocation patterns 24 h after labelling. Simultaneously, integrative nitrogen competition was quantified by examining total nitrogen capture, total nitrogen pools and total nitrogen allocation.Stipa neighbors reduced inorganic soil nitrogen content to a greater extent than didBromus plants. Blue oak seedlings responded to lower soil nitrogen content by allocating lower amounts of nitrogen per unit of biomass producing higher root length densities and reducing the nitrogen content of root tissue. In addition, blue oak seedlings growing with the perennial grass exhibited greater rates of¹⁵N uptake, on a root mass basis, compensating for higher soil nitrogen competition inStipa neighborhoods. Our findings suggest that while oak seedlings have lower rates of nitrogen capture than herbaceous neighbors, oak seedlings exhibit significant changes in nitrogen allocation and nitrogen uptake rates which may offset the competitive effect annual or perennial grasses have on soil nitrogen content.     

Cyanide controls enzymes involved in lipid and sugar catabolism in dormant apple embryos during culture

The activities of alkaline lipase (EC 3.1.1.3, AlkL), isocitrate lyase (EC 4.1.3.1. ICL), pyruvate kinase (EC 2.7.1.40. PK) and glucose–6–phosphate dehydrogenase (EC 1.1.1.49, G6PDH) were determined in cultured, dormant embryos of apple (Malus domestica Borb. cv. Antonówka), pretreated with gaseous HCN. The C₆/C₁ , ratio was estimated in the same material. The activities of AlkL and ICL were not stimulated by HCN pretreatment until the period of maximum stimulation of germination. The activity of G6PDH was inhibited by cyanide only late during the culture of embryos. Therefore, the changes in these activities are considered to be the result and not the cause of enhanced germination. On the other hand, also PK, active very early during the culture of embryos, was modified as a result of the treatment. The cyanide-induced changes in activity of this enzyme in cotyledons (inhibition followed by stimulation) were similar to those in the whole embryo, whereas its changes in the embryonal axis (stimulation followed by inhibition) resembled CN-induced changes in PK in axes of apple seeds submitted to cold stratification (Bogatek and Lewak 1988). The estimation of C₆/C₁ ratios partly confirmed these observations. A role of HCN-induced modifications of PK activity in embryonal dormancy is proposed.     

Microbial growth on carbon monoxide

The utilization of carbon monoxide as energy and/or carbon source by different physiological groups of bacteria is described and compared. Utilitarian CO oxidation which is coupled to the generation of energy for growth is achieved by aerobic and anaerobic eu- and archaebacteria. They belong to the physiological groups of aerobic carboxidotrophic, facultatively anaerobic phototrophic, and anaerobic acetogenic, methanogenic or sulfate-reducing bacteria. The key enzyme in CO oxidation is CO dehydrogenase which is a molybdo iron-sulfur flavoprotein in aerobic CO-oxidizing bacteria and a nickel-containing iron-sulfur protein in anaerobic ones. In carboxidotrophic and phototrophic bacteria, the CO-born CO₂ is fixed by ribulose bisphosphate carboxylase in the reductive pentose phosphate cycle. In acetogenic, methanogenic, and probably in sulfate-reducing bacteria, CODH/acetyl-CoA synthase directly incorporates CO into acetyl-CoA.In plasmid-harbouring carboxidotrophic bacteria, CO dehydrogenase as well as enzymes involved in CO₂ fixation or hydrogen utilization are plasmid-encoded. Structural genes encoding CO dehydrogenase were cloned from carboxidotrophic, acetogenic and methanogenic bacteria. Although they are clustered in each case, they are genetically distinct.Soil is a most important biological sink for CO in nature. While the physiological microbial groups capable of CO oxidation are well known, the type and nature of the microorganisms actually representing this sink are still enigmatic. We also tried to summarize the little information available on the nutritional and physicochemical requirements determining the sink strength. Because CO is highly toxic to respiring organisms even in low concentrations, the function of microbial activities in the global CO cycle is critical.     

Effect of n-6 and n-3 polyunsaturated fatty acids ingestion on rat liver membrane-associated enzymes and fluidity

The influences of diets having different fatty acid compositions on the fatty-acid content, desaturase activities, and membrane fluidity of rat liver microsomes have been analyzed. Weanling male rats (35–45 g) were fed a fat-free semisynthetic diet supplemented with 10% (by weight) marine fish oil (FO, 12.7% docosahexaenoic acid and 13.8% eicosapentaenoic acid), evening primrose oil (EPO, 7.8% γ-linolenic acid and 70.8% linoleic acid) or a mixture of 5% FO-5% EPO. After 12 weeks on the respective diets, animals fed higher proportions of (n-3) polyunsaturated fatty acids (FO group) consistently contained higher levels of 20:3(n-6), 20:5(n-3), 22:5(n-3), and 22:6(n-3), and lower levels of 18:2(n-6) and 20:4(n-6), than those of the EPO (a rich source of (n-6) polyunsaturated fatty acids) or the FO + EPO groups. Membrane fluidity, as estimated by the reciprocal of the order parameter S_DPH, was higher in the FO than in the EPO or the FO + EPO groups, and the n-6 fatty-acid desaturation system was markedly affected.