The influence of spermine on the structural dynamics of yeast tRNAPhe

A tRNA^Phe derivative carrying ethidium at position 37 in the anticodon loop has been used to study the effect of spermine on conformational transitions of the tRNA. As previously reported (Ehrenberg, M., Rigler, R. and Wintermeyer, W. (1979) Biochemistry 18, 4588–4599) in the tRNA derivative the ethidium is present in three states (T₁–T₃) characterized by different fluorescence decay rates. T-jump experiments show two transitions between the states, a fast one (relaxation time 10–100 ms) between T₁ and T₂, and a slow one (100–1000 ms) between T₂ and T₃. In the presence of spermine the fast transition shows a negative temperature coefficient indicating the existence of a preequilibrium with a negative reaction enthalpy. Spermine shifts the distribution of states towards T₃, as does Mg²⁺, but the final ratio $\text{[}\text{T}{}_2\text{]}\text{[}\text{T}{}_1\text{]}$ obtained with spermine is higher than with Mg²⁺, which we tentatively interpret to mean that spermine stabilizes one particular conformation of the anticodon loop.     

Effects of three herbicides on soil microbial biomass and activity

Three post-emergence herbicides (2,4-D, picloram and glyphosate) were applied to samples of an Alberta agricultural soil at concentrations of 0, 2, 20, and 200 μg g⁻¹. The effects of these chemicals on certain microbial variables was monitored over 27 days. All herbicides caused enhancement of basal respiration but only for 9 days following application, and only for concentrations of 200 μg g⁻¹. Substrate-induced respiration was temporarily depressed by 200 μg g⁻¹ picloram and 2,4-D, and briefly enhanced by 200 μg g⁻¹ glyphosate. It is concluded that because changes in microbial variables only occurred at herbicide concentrations of much higher than that which occurs following field application, the side-effects of these chemicals is probably of little ecological significance.     

Protein phylogeny of translation elongation factor EF-1α suggests microsporidians are extremely ancient eukaryotes

Partial regions of the mRNA encoding a major part of translation elongation factor 1 (EF-1) from a mitochondrion-lacking protozoan,Glugea plecoglossi, that belongs to microsporidians, were amplified by polymerase chain reaction (PCR) and their primary structures were analyzed. The deduced amino acid sequence was highly divergent from typical EF-1's of eukaryotes, although it clearly showed a eukaryotic feature when aligned with homologs of the three primary kingdoms. Maximum likelihood (ML) analyses on the basis of six different stochastic models of amino acid substitutions and a maximum parsimony (MP) analysis consistently suggest that among eukaryotic species being analyzed,G. plecoglossi is likely to represent the earliest offshoot of eukaryotes. Microsporidians might be the extremely ancient eukaryotes which have diverged before an occurrence of mitochondrial symbiosis. Sequence availability: The nucleotide sequence data reported here appear in the GSDB, DDBJ, EMBL, and NCBI databases with the accession number D32139     

Comparative study of two meromictic basins of Lake Banyoles (Spain) with sulphur phototrophic bacteria

The annual limnological dynamics of two meromictic basins of Lake Banyoles (C-III and C-IV) have been studied and compared on the basis of their physical, chemical and biological characters. Stability values calculated for both basins gave 865 g cm cm⁻² and 495 g cm cm⁻² for C-III and C-IV respectively. These values are in agreement with the fact that C-IV was almost completely mixed during winter. In this basin, during stratification, the monimolimnion increased in thickness as the stability increased. Isolation of the respective monimolimnia resulted in the development of anoxic conditions and the accumulation of sulphide in both C-III and C-IV, which favoured the development of dense populations of sulfur phototrophic bacteria. The purple sulphur bacterium Chromatium minus and the green sulphur bacterium Chlorobium phaeobacteroides were identified as the main components of these photosynthetic populations. The different depths at which the O₂/H₂S boundary was situated in both basins (and consequently the different light intensity reaching this zone) determined the growth of these bacteria. Light intensities at the chemocline of C-IV reached values up to 5% of surface incident light. In contrast, in C-III this variable was sensibly lower, with values depending on season and seldom reaching 1%. Phototrophic bacteria were consequently found earlier in C-IV than in C-III, where no significant concentrations were found until August. Finally stability is discussed as an important factor controlling chemical and biological dynamics in meromictic lakes.     

Decomposition of Eucalyptus globulus leaves and three native leaf species (Alnus glutinosa, Castanea sativa and Quercus faginea) in a Portuguese low order stream

Leaf decomposition of the exotic evergreen Eucalyptus globulus (eucalyptus), and three native deciduous tree species, Alnus glutinosa (alder), Castanea sativa (chestnut) and Quercus faginea (oak), was compared in a second order stream in Central Portugal. Changes in dry weight, nitrogen and polyphenolic compounds and microbial colonization were periodically assessed for three months.Negative exponential curves fit the leaf weight loss with time for all leaf species. Mass loss rate was in the order alder (K = 0.0161) > chestnut (K = 0.0079) > eucalyptus (K = 0.0068) > oak (K = 0.0037). Microbial colonization followed the same pattern as breakdown rates. Evidence of fungal colonization was observed in alder after 3 days in the stream, whereas it took 21 days in oak leaves to have fungal colonization. Fungal diversity was leaf species-dependent and increased with time. In all cases, percent nitrogen per unit leaf weight increased, at least, at the initial stages of decay while soluble polyphenolics (expressed as percentage per unit leaf weight) decreased rapidly in the first month of leaves immersion.Intrinsic factors such as nitrogen and polyphenolic content may explain differences in leaf decomposition. The possible incorporation of eucalyptus litter into secondary production in a reasonable time span is suggested, although community balance and structure might be affected by differences in allochthonous patterns determined by eucalyptus monocultures.     

Spatial patterns and relationships between phytoplankton, zooplankton and water quality in the Saimaa lake system, Finland

The interactions between phytoplankton and zooplankton were studied in two large lakes in the Saimaa lake system, Finland. Both are subjected to substantial waste water loading, and exhibit a clear trophic gradient between the loaded and unloaded areas. The phytoplankton and zooplankton were compared in terms of composition, abundance and biomass at 34–39 stations located in different parts of the lakes. At least four mechanisms were thought to affect the composition of plankton communities: (1) the amount of nutrients (trophic gradient), (2) grazing of algae by herbivores, (3) the effect of the algal species composition on feeding by zooplankters (large, colonial algae in the more loaded parts of the lakes) and (4) the regeneration and reorganization of nutrients.     

The rare occurrence of plant tissue culture contamination by Methylobacterium mesophilicum

A pink-pigmented, facultative methylotrophic (PPFM) bacterium, Methylobacterium mesophilicum, which is found on the leaf surface of most plants, has been reported to be a covert contaminant of tissue cultures initiated from Glycine max (soybean) leaves and seeds by Holland and Polacco (1992). The bacteria can be detected as pink colonies when leaves are pressed or tissue culture homogenates are plated on a medium with methanol as the sole carbon source. Since the presence of contaminating bacteria can confound any biochemical results obtained with such cultures (Holland and Polacco 1992), we wanted to determine the extent of the contamination of our tissue cultures of soybean and other species. No PPFMs were detected in any soybean culture we have, and previous results describing the biochemical characteristics of ureide utilization by one of our soybean suspension cultures (27C) also indicates that PPFM bacteria were not present. Analysis of about 200 other strains of 11 different species maintained in this lab showed that only three of about 160 callus cultures, recently initiated from Datura innoxia leaves, contained PPFMs. The D. innoxia leaves did have PPFMs on their surface but in most cases they did not survive the surface disinfestation and culture regimes. Thus PPFM bacterial contamination should not be a serious problem in most plant tissue cultures.Abbreviations AMS ammonium mineral salts medium - PPFM pink-pigmented facultative methylotrophic bacteria     

A comparative study of ciliated protozoa communities in activated-sludge plants

Abstract: Ciliated protozoa present in ten activated sludge plants at Madrid (Spain) were identified. The abundance of key groups of ciliates was determined at each plant; attached ciliates made up the most abundant and representative group. Multivariate statistical analysis was employed to study relationships between ciliates and both the physico-chemical and operational parameters of the plants. Partial correlation analysis revealed: (1) The indicator value of attached ciliates in assessing management and performance of the activated sludge process, (2) the relationship of swimming ciliates with short-aged sludges and lower quality effluents and (3) the direct association between swimming-crawling ciliates and bad settlement conditions of the sludge. Factor analysis showed the associations of the most frequent species of ciliates with the operational parameters of the plants, suggesting the indicator value of some of the species: Vorticella striata was related with poor quality of effluent; Aspidisca cicada with stable plant conditions, and Litonotus lamella with a deficiently settling sludge.     

The heterogeneous nature of microbial products as shown by solid-state13C CP/MAS NMR spectroscopy

Homoionic Na-, Ca-, and Al-clays were prepared from the <2 m fractions of Georgia kaolinite and Wyoming bentonite and mixed with sand to give artificial soils with 5, and 25% clay. The artificial soils were inoculated with microbes from a natural soil before incubation. Unlabelled and uniformly¹³C-labelled (99.9% atom) glucose were incorporated into the artificial soils to study the effects of clay types, exchangeable cations and clay contents on the mineralization of glucose-carbon and glucose-derived organic materials. Chemical transformation of glucose-carbon upon incorporation into microbial products and metabolites, was followed using solid-state¹³C CP/MAS NMR spectroscopy.There was a significant influence of exchangeable cations on the mineralization of glucose-carbon over a period of 33 days. At 25% clay content, mineralization of glucose-carbon was highest in Ca-soils and lowest in Al-soils. The influence of exchangeable cations on mineralization of glucose-carbon was more pronounced in soils with bentonite clay than those with kaolinite clay. Statistical analysis of data showed no overall effect of clay type on mineralization of glucose-carbon. However, the interactions of clay type with clay content and clay type with clay content and exchangeable cations were highly significant. At 25% clay content, the mineralization of glucose-carbon was significantly lower in Na- and Al-soils with Wyoming bentonite compared with Na- and Al-soils with Georgia kaolinite. For Ca-soils this difference was not significant. Due to the increased osmotic tension induced by the added glucose, mineralization of glucose-carbon was slower in soils with 5% clay than soils with 25% clay.Despite the differences in the chemical and physical characteristics of soils with Ca-, Na- and Al-clays, the chemical composition of organic materials synthesised in these soils were similar in nature. Assuming CP/MAS is quantitative, incorporation of uniformly¹³C-labelled glucose (99.9% atom) in these soils resulted in distribution of carbon in alkyl (24–25%), O-alkyl (56–63%), carbonyl (11–15%) and small amounts of aromatic and olefinic carbon (2–4%). However, as decomposition proceeded, the chemistry of synthesised material showed some changes with time. In the Ca- and Na-soils, the proportions of alkyl and carbonyl carbon decreased and that of O-alkyl carbon increased with time of incubation. However, the opposite trend was found for the Al-soil.Proton-spin relaxation editing (PSRE) subspectra clearly showed heterogeneity within the microbial products. Subspectra of the slowly-relaxing (long T₁(H)) domains were dominated by alkyl carbon in long- and short-chain structures. The signals due to N-alkyl (55 ppm) and carbonyl carbon were also strong in these subspectra. These subspectra were very similar to those obtained for microbial and fungal materials and were probably microbial tissues attached to clay surfaces by polysaccharide extracellular mucilage. Subspectra of fast-relaxing (short T₁(H)) domains comprised mostly O-alkyl and carbonyl carbon and were probably microbial metabolites released as neutral and acidic sugars into the extracellular environment, and strongly sorbed by clay surfaces.     

The effects of mycorrhizal roots on litter decomposition, soil biota, and nutrients in a spodosolic soil

We studied the effects of mycorrhizal pitch pine (Pinus rigida) roots on litter decomposition, microbial biomass, nematode abundance and inorganic nutrients in the E horizon material of a spodosolic soil, using field microcosms created in a regenerating pitch pine stand in the New Jersey Pinelands. Pine roots stimulated litter decomposition by 18.7% by the end of the 29 month study. Both mass loss and N and P release from the litter were always higher in the presence of roots than in their absence. Nutrient concentrations in decomposing litter were similar, however, in the presence and absence of roots, which suggests that the roots present in the with-root treatment did not withdraw nutrients directly from the litter. The soil was slightly drier in the presence of roots, but there was no discernible effect on soil microbial biomass. The effects of roots on soil extractable inorganic nutrients were inconsistent. Roots, however, were consistently associated with higher numbers of soil nematodes. These results suggest that, in soils with low total C and N contents, roots stimulate greater activity of the soil biota, which contribute, in turn, to faster litter decomposition and nutrient release.Contribution No. 95-22 from the Institute of Marine and Coastal Sciences.Contribution No. 95-22 from the Institute of Marine and Coastal Sciences.