A 71-kDa protein from Halobacterium salinarium belongs to a ubiquitous P-loop ATPase superfamily with head-rod-tail structure

The nucleotide sequence of a genomic fragment from Halobacterium salinarium containing an open reading frame encoding a protein with a calculated molecular mass of 71 kDa was determined. Database searches revealed that this protein, Hp71, has similarities to eukaryotic cytoskeletal proteins. Heterologous production of Hp71 in Escherichia coli allowed the isolation of anti-Hp71 antibodies. The antibodies were used (1) to verify the production of Hp71 in H. salinarium and (2) to determine its cytoplasmic localization by immune electron microscopy. Homologous overproduction of Hp71 in H. salinarium and heterologous production in Haloferax volcanii resulted in modifications of cell morphology from rods to extended rods, and from pleiomorphic cells to rods, respectively. Structure prediction methods indicated that Hp71 has a head-rod-tail configuration, including an N-terminal domain with a nucleotide binding motif (P-loop), and an extended discontinuous coiled-coil domain of 330 amino acids. To identify related proteins, the complete genomes of Haemophilus influenzae, Mycoplasma genitalium, and Methanococcus jannaschii were searched for deduced proteins with extended coiled-coil domains. Only one or two proteins were found for each organism, showing that Hp71 is one of only a few prokaryotic intracellular proteins with extended coiled-coil domains. The phenotype upon overproduction and the similarity of Hp71 to the SMC superfamily of P-loop head-rod-tail proteins (named after SMC1, which is involved in the “stability of minichromosomes” in yeast) indicate that Hp71 might be involved in cytoskeleton formation and/or chromosome partitioning in H. salinarium. Received: 25 March 1997 / Accepted: 11 August 1997     

Cleavage of chitinous elicitors from the ectomycorrhizal fungus Hebeloma crustuliniforme by host chitinases prevents induction of K+ and Cl− release, extracellular alkalinization and H2O2 synthesis of Picea abies cells

Rapid reactions comprising efflux of K⁺ and Cl⁻, phosphorylation of a 63-kDa protein (pp63), extracellular alkalinization and synthesis of H₂O₂ are equally induced in cells of Picea abies (L.) Karst. by chitotetraose, colloidal chitin and cell wall elicitors from the ectomycorrhizal fungus Hebeloma crustuliniforme (Bull. ex Fries.) Quél. an ectomycorrhizal partner of spruce. Cleavage of fungal cell wall elicitors and of artificial chitin elicitors to monomeric and dimeric fragments by apoplasmic spruce chitinases (36-kDa class I chitinase, pI 8.0, and 28-kDa chitinase, pI 8.7; EC 3.2.1.14) equally prevented induction of these rapid reactions. Also, N-acetylglucosamine oligomers and elicitors from the fungal cell walls showed a similar dependence of their activity on the degree of polymerisation. From these results it is suggested that, during ectomycorrhiza formation, only some of the chitin-derived elicitors reach their receptors at the plant plasma membrane, initiating reactions of the hypersensitive response in the host cells. The remaining fungal elicitors will be degraded to varying extents by wall-localized chitinases of the host root, reducing the defence reactions of the plant and allowing symbiotic interactions of both organisms. Received: 6 January 1997 / Accepted: 14 March 1997     

Predation impact of Cyclops vicinus on the rotifer community in Lake Constance in spring

The predation impact of Cyclops vicinus on rotifers was studiedunder near-natural conditions in small enclosures to evaluatewhether copepod predation is responsible for the decline ofrotifers in Lake Constance in spring. Cyclops vicinus fed selectivelyon Synchaeta spp.; Keratella and Polyarthra spp. were not selectedfor. Predation rates increased with prey density up to a maximumof 37 Synchueta day^–1 at a density of 1.6 x 10⁶ Synchaetam^–2, i.e. at -1200 Synchaeta l^–1. Calculation ofcropping rates suggests that Cyclops alone can control the abundanceof Synchaeta in spring, i.e. that mainly Cyclops is responsiblefor the decline of Synchaeta species in Lake Constance in May.     

Changes in microvascular fluid filtration capacity during 120 days of 6 degrees head-down tilt.

We used venous congestion strain gauge plethysmography (VCP) to measure the changes in fluid filtration capacity (K(f)), isovolumetric venous pressure (Pv(i)), and blood flow in six volunteers before, on the 118th day (D118) of head-down tilt (HDT), and 2 days after remobilization (Post). We hypothesized that 120 days of HDT cause significant micro- and macrovascular changes. We observed a significant increase in K(f) from 3.6 +/- 0.4 x 10(-3) to 5.7 +/- 0.9 x 10(-3) ml. min(-1). 100 ml(-1). mmHg(-1) (+51.4%; P < 0.003), which returned to pretilt values (4.0 + 0.4 x 10(-3) ml. min(-1). 100 ml(-1). mmHg(-1)) after remobilization. Similarly, Pv(i) increased from 13.4 +/- 2.1 mmHg to 28.9 +/- 2.8 mmHg (+105.8%; P < 0.001) at D118 and was not significantly different at Post (12.4 +/- 2.6 mmHg). Blood flow decreased significantly from 2.3 +/- 0.3 to 1.3 +/- 0.2 ml. min(-1). 100 ml tissue(-1) at D118 and was found elevated to 3.4 +/- 0.7 ml. min(-1). 100 ml tissue(-1) at Post. We believe that the increased K(f) is caused by a higher microvascular water permeability. Because this may result in edema formation, it could contribute to the alterations in fluid homeostasis after exposure to microgravity.     

Persistent organochlorine pesticides detected in blood and tissue samples of vultures from different localities in South Africa

Gaschromatography was used to establish the presence of quantifiable residues of 14 persistent chlorinated hydrocarbon pollutants in whole blood, clotted blood, heart, kidney, liver and muscle samples obtained from individual African whitebacked (Pseudogyps africanus), Cape griffon (Gyps coprotheres) and Lappetfaced (Torgos tracheliotos) vultures from different localities in South Africa. The levels of pesticides measured in whole blood samples of live specimens were compared between nestlings from two natural breeding colonies, adults from a wildlife area and birds held in captivity. Statistically significant (P<0.05) differences between populations were detected in geometric means calculated for γ-BHC (lindane), α(cis)-chlordane and α-endosulfan. Five of the organochlorine contaminants displayed significant variations between concentrations detected in the clotted blood, organs and muscles excised from vulture carcasses. This includes residues of γ-BHC, α-chlordane, dieldrin, β-endosulfan and heptachlor epoxide. Values of the respective biocides measured in vulture samples were generally low in comparison to results documented for a number of avian species. Although no threat is posed by any of the organochloride pesticides, continual monitoring of especially breeding colonies is recommended. Furthermore, the suitability of African whitebacked vulture nestlings as basic bioindicators is highly advocated.     

Acid Tolerance of Streptococcus macedonicus as Assessed by Flow Cytometry and Single-Cell Sorting

An in situ flow cytometric viability assay employing carboxyfluorescein diacetate and propidium iodide was used to identify Streptococcus macedonicus acid tolerance phenotypes. The logarithmic-phase acid tolerance response (L-ATR) was evident when cells were (i) left to autoacidify unbuffered medium, (ii) transiently exposed to nonlethal acidic pH, or (iii) systematically grown under suboptimal acidic conditions (acid habituation). Stationary-phase ATR was also detected; this phenotype was gradually degenerated while cells resided at this phase. Single-cell analysis of S. macedonicus during induction of L-ATR revealed heterogeneity in both the ability and the rate of tolerance acquisition within clonal populations. L-ATR was found to be partially dependent on de novo protein synthesis and compositional changes of the cell envelope. Interestingly, acid-habituated cells were interlaced in lengthier chains and exhibited an irregular pattern of active peptidoglycan biosynthesis sites when probed with BODIPY FL vancomycin. L-ATR caused cells to retain their membrane potential after lethal challenge, as judged by ratiometric analysis with oxonol [DiBAC₄(3)]. Furthermore, F-ATPase was important during the induction of L-ATR, but in the case of a fully launched response, inhibition of F-ATPase affected acid resistance only partially. Activities of both F-ATPase and the glucose-specific phosphoenolpyruvate-dependent phosphotransferase system were increased after L-ATR induction, distinguishing S. macedonicus from oral streptococci. Finally, the in situ viability assessment was compared to medium-based recovery after single-cell sorting, revealing that the culturability of subpopulations with identical fluorescence characteristics is dependent on the treatments imposed to the cells prior to acid challenge.     

Late‐Holocene fire history in a forest‐grassland mosaic in southern Brasil: Implications for conservation

Question: Is the diverse mosaic of forest/grassland (Campos) vegetation on the hills in the Porto Alegre region natural or of anthropogenic origin? What are the best approaches to management and conservation of forest/grassland mosaics in southern Brazil? Location: 280 m a.s.l., Rio Grande do Sul State (30°04′32″S; 51°06′05″W, southern Brazil. Methods: A 50-cm long radiocarbon dated sediment core from a swamp on Morro Santana was analysed for pollen and charcoal, and multivariate data analysis was used to reconstruct past vegetation and fire dynamics. Results: The formation of swamp deposits is related to a change to wetter climatic conditions since 1230 cal yr BP. The diverse forest/grassland mosaic existed already at that time and can be seen as natural in origin as it has been also shown from other studies in southern Brazil. Since 580 cal yr BP, forests expanded continuously. The marked higher occurrence of the pioneer Myrsine during the last 70 years, indicates a change in the disturbance regime. In the past, vegetation has been influenced by mostly anthropogenic fire, set first by Amerindians and later by European settlers. Conclusions: Management for conservation of forest/grassland mosaics should take into account, first, that grasslands are remnants of earlier drier Holocene periods and not a result of deforestation and, second, the history of disturbance by grazing and fire. Suppression of grazing and burning has likely resulted in a trend towards more woody vegetation under modern wet climatic conditions. If management for conservation excludes fire, the present grassland patches will tend to disappear due to forest expansion under the modern humid climate. Maintaining or reintroducing cattle grazing in conservation areas could be an alternative to fire.