Microfungal species composition and fungal biomass in a coniferous forest soil polluted by alkaline deposition

Isolations of soil microfungi from the humus (F/H-layer) of a coniferous forest soil which was either unpolluted (pH 4.1) or polluted (pH 6.6) for 25 years by deposition of alkaline dust, were made by soil washing and spore plating. Both techniques revealed similar changes in species composition. Alkaline dust exposure caused a reduction in overall species numbers, but led to higher relative isolation frequencies of Mortierella alpina, Oidiodendron tenuissimum, Penicillium montanese, Sagenomella verticillata, and Trichosporiella sporotrichioides. The incidence of M. isabellina, O. cf. clamydosporium, P. spinulosum, Penicillium sp. 1, P. sclerotiorum, Trichoderma viride, and Verticillium bulbillosum was reduced on polluted sites. The amount of the mainly fungal-derived phospholipid fatty acid 18 : 26 decreased by 23%, while the amount of ergosterol increased by 9% in the polluted soil. Offprint requests to: H. Fritze.     

Homozygotes for the autosomal dominant neoplasia syndrome (MEN1).

Families in which both parents are heterozygotes for the same autosomal dominant neoplasia syndrome are extremely unusual. Recently, we had the unique opportunity to evaluate three symptomatic siblings from the union between two unrelated individuals affected by multiple endocrine neoplasia type 1 (MEN1). When the three siblings and their parents and relatives were genotyped for 12 markers tightly linked to the MEN1 locus, at 11q13, two of the siblings were found to be homozygotes, and one a heterozygote, for MEN1. With regard to the MEN1 syndrome, no phenotypic differences were observed between the two homozygotes and the heterozygotes. However, the two homozygotes showed unexplained infertility, which was not the case for any of the heterozygotes. Thus, MEN1 appears to be a disease with complete dominance, and the presence of two MEN1 alleles with mutations of the type that occur constitutionally may be insufficient for tumor development.     

Causes and consequences of egg mass variation between and within blue tit clutches

Causes of egg-size variation between and within clutches were studied in clutches of the blue tit ( Parus caeruleus L.). We measured the mass of each egg in the laying sequence in unmanipulated clutches, in clutches of parents experimentally supplied with extra food before egg-laying, and in clutches of parents supplemented with extra food after the start of egg-laying. Hatchlings were weighed at an age of two days and their mass was found to be positively related to egg mass. No general trend of decreasing or increasing egg mass was found within the laying sequence. Females provided with extra food before egg-laying laid clutches with significantly less variation in egg mass than did control females. The reason for this was that the first-laid egg of unmanipulated females was lighter than the rest of the eggs in the clutch. This pattern disappeared in clutches of females receiving extra food. Thus, the reduction in egg mass variation among clutches of foodsupplemented females depended on an ability of these females, in contrast to control females, to lay a first egg of the same mass as the rest of the clutch. Eggs laid after the initiation of incubation were significantly heavier than equivalent eggs in those clutches where incubation started after clutch completion. The difference was small, however, and the adaptive significance of the finding is questionable. We argue that intra-clutch variation in egg mass is connected with greater fitness consequences than in inter-clutch variation. Furthermore, our results indicate that energetical constraints on the laying female are more important as a cause of the observed intra-clutch variation in egg mass than are adaptive responses to the environment.     

Soil and rhizosphere microorganisms have the same Q10 for respiration in a model system

We compared the Q₁₀ relationship for root‐derived respiration (including respiration due to the root, external mycorrhizal mycelium and rhizosphere microorganisms) with that of mainly external ectomycorrhizal mycelium and that of bulk soil microorganisms without any roots present. This was studied in a microcosm consisting of an ectomycorrhizal Pinus muricata seedling growing in a sandy soil, and where roots were allow to colonize one soil compartment, mycorrhizal mycelium another compartment, and the last compartment consisted of root‐ and mycorrhiza‐free soil. The respiration rate in the bulk soil compartment was 30 times lower than in the root compartment, while that in the mycorrhizal compartment was six times lower. There were no differences in Q₁₀ (for 5–15°C) between the different compartments, indicating that there were no differences in the temperature relationship between root‐associated and non‐root‐associated organisms. Thus, there are no indications that different Q₁₀ values should be used for different soil organism, bulk soil or rhizosphere‐associated microorganisms when modelling the effects of global climate change.     

Crystal structure of the superantigen staphylococcal enterotoxin type A.

Staphylococcal enterotoxins are prototype superantigens characterized by their ability to bind to major histocompatibility complex (MHC) class II molecules and subsequently activate a large fraction of T-lymphocytes. The crystal structure of staphylococcal enterotoxin type A (SEA), a 27 kDa monomeric protein, was determined to 1.9 A resolution with an R-factor of 19.9% by multiple isomorphous replacement. SEA is a two domain protein composed of a beta-barrel and a beta-grasp motif demonstrating the same general structure as staphylococcal enterotoxins SEB and TSST-1. Unique for SEA, however, is a Zn2+ coordination site involved in MHC class II binding. Four amino acids including Ser1, His187, His225 and Asp227 were found to be involved in direct coordination of the metal ion. SEA is the first Zn2+ binding enterotoxin that has been structurally determined.     

Characterization of a folding intermediate of human carbonic anhydrase II: probing local mobility by electron paramagnetic resonance.

The spin-labeling method was used to investigate human carbonic anhydrase, HCA II, undergoing unfolding induced by guanidine-HCI (Gu-HCI). The spin-probe, N-(2,2,5,5-tetramethyl-1-yloxypyrrolidinyl-3-yl)iodoacetamide, was attached covalently to the single cysteine (position 206) in the enzyme. The electron paramagnetic resonance spectrum of the folded structure showed the characteristic slow motional spectra. When the concentration of the denaturing agent, Gu-HCI, was gradually increased, new spectral components with narrower lines evolved to give complex electron paramagnetic resonance spectra, apparently containing superimposed contributions from several components of different mobility. By a differentiation technique, it was possible to follow the relative increase of the narrow components as a function of Gu-HCI concentration. The amplitude of difference spectra versus Gu-HCI concentration showed two distinct maxima, indicating the existence of a folding intermediate state/structure. The results were found to agree with optical absorption data, which showed similar transitions at the same Gu-HCI concentrations. From line-shape simulations assuming a Brownian diffusion model, the rotational diffusion constants for the spin-label in the folded, folding intermediate, and unfolded structures were determined. The relative abundances of the three conformations in the region 0-4 M Gu-HCI were obtained by least squares fitting of the simulated spectra to the experimental ones. The folding intermediate was found to have a maximum population of 39 +/- 4% at approximately 0.7 M Gu-HCI.     

Domain Evolution in the α-Amylase Family

The available amino acid sequences of the α-amylase family (glycosyl hydrolase family 13) were searched to identify their domain B, a distinct domain that protrudes from the regular catalytic (β/α)₈-barrel between the strand β3 and the helix α3. The isolated domain B sequences were inspected visually and also analyzed by Hydrophobic Cluster Analysis (HCA) to find common features. Sequence analyses and inspection of the few available three-dimensional structures suggest that the secondary structure of domain B varies with the enzyme specificity. Domain B in these different forms, however, may still have evolved from a common ancestor. The largest number of different specificities was found in the group with structural similarity to domain B from Bacillus cereus oligo-1,6-glucosidase that contains an α-helix succeeded by a three-stranded antiparallel β-sheet. These enzymes are α-glucosidase, cyclomaltodextrinase, dextran glucosidase, trehalose-6-phosphate hydrolase, neopullulanase, and a few α-amylases. Domain B of this type was observed also in some mammalian proteins involved in the transport of amino acids. These proteins show remarkable similarity with (β/α)₈-barrel elements throughout the entire sequence of enzymes from the oligo-1,6-glucosidase group. The transport proteins, in turn, resemble the animal 4F2 heavy-chain cell surface antigens, for which the sequences either lack domain B or contain only parts thereof. The similarities are compiled to indicate a possible route of domain evolution in the α-amylase family. Received: 4 December 1996 / Accepted: 13 March 1997