Winter phytoplankton community structure in three shallow temperate lakes during ice cover

The general model of seasonal phytoplankton succession in temperate lakes suggests that winter phytoplankton growth is minimal under ice-cover. However, some studies have found diverse phytoplankton communities during winter. The primary objectives of this study were to determine the species composition and the changes in the winter phytoplankton community structure under the ice. For 2 consecutive winters, phytoplankton samples were collected under ice-cover at 4 sites on 3 lakes in Arrowwood National Wildlife Refuge (ANWR), near Pingree, North Dakota. Ninety taxa were identified and enumerated. Densities of several of these taxa frequently exceeded 10⁶ cells l^–1. The winter phytoplankton communities in these lakes were dominated by flagellates, principally cryptomonads, a synurophyte (Synura uvella), small chrysophytes (Chrysococcus spp., Kephyrion spp.) and a dinoflagellate (Peridinium aciculiferum), as well as non-flagellate microchlorophytes (Monoraphidium spp., Ankistrodesmus spp., and Pseudodictyosphaerium sp.), a cyanobacterium (Gloeocapsa aeruginosa) and centric diatoms (Stephanodiscus minutulus, S. parvus and Cyclotella meneghiniana).     

Conformational dynamics of the molecular chaperone Hsp90 in complexes with a co-chaperone and anticancer drugs

The molecular chaperone Hsp90 is essential for the correct folding, maturation and activation of a diverse array of client proteins, including several key constituents of oncogenic processes. Hsp90 has become a focus of cancer research, since it represents a target for direct prophylaxis against multistep malignancy. Hydrogen-exchange mass spectrometry was used to study the structural and conformational changes undergone by full-length human Hsp90beta in solution upon binding of the kinase-specific co-chaperone Cdc37 and two Hsp90 ATPase inhibitors: Radicicol and the first-generation anticancer drug DMAG. Changes in hydrogen exchange pattern in the complexes in regions of Hsp90 remote to the ligand-binding site were observed indicating long-range effects. In particular, the interface between the N-terminal domain and middle domains exhibited significant differences between the apo and complexed forms. For the inhibitors, differences in the interface between the middle domain and the C-terminal domain were also observed. These data provide important insight into the structure of the biologically active form of the protein.     

Gender-influenced obesity QTLs identified in a cross involving the KK type II diabetes-prone mouse strain

The inheritance of adiposity and related traits has been investigated in the obese, diabetes-prone KK/HlLt (KK) and the lean, normoglycemic C57BL/6J (B6) mouse strains, their F₁ hybrids, and a large intercross generation. Adiposity index (AI) was defined as the sum of four fat depot weights divided by body weight. Both male and female KK mice were obese, but AI values averaged twofold higher in females than in males. In contrast, B6 females were slightly more lean than males. A genome-wide search revealed several qualitative trait loci (QTLs) affecting AI. The proximal region of Chromosome (Chr) 9 has a large effect on AI, with a much stronger effect in females (lod = 6.3) than in males (lod = 2.7). The data for females fit a model in which a dominant allele from KK increases AI by 30%, with the lod score peak falling between markers D9Mit66 and D9Mit328. This QTL has large effects on inguinal and mesenteric fat pad weights, with smaller effects on gonadal and retroperitoneal fat pads. The region of Chr 9 containing this QTL has extensive homology to human Chr 11q. An X-linked QTL affecting AI was evident in males (lod = 3.77), but not females (lod = 0.7). Exclusion of mesenteric fat from male AI resulted in an increased lod score (lod = 5.0) at 8 cM distal to DXMit166. A suggestive AI QTL (lod = 4.2), differentially affecting males, was localized to Chr 18 near the glucocorticoid receptor locus. A region of Chr 7 had a strong effect on body weight (lod = 6.9), a significant effect on inguinal fat% (lod = 4.4), and a suggestive effect on AI in females (lod = 4.1). Plasma leptin levels were associated with genotypes on Chr 9 (lod = 5.9) and Chr 7 (lod = 4.2). A region of Chr 1 had a suggestive effect on fasted blood glucose (lod = 3.6). Received: 23 March 1999 / Accepted: 2 June 1999     

Monomeric structure of the human EphB2 sterile alpha motif domain

The sterile alpha motif (SAM) domain is a protein module found in many diverse signaling proteins. SAM domains in some systems have been shown to self-associate. Previous crystal structures of an EphA4-SAM domain dimer (Stapleton, D., Balan, I., Pawson, T., and Sicheri, F. (1999) Nat. Struct. Biol. 6, 44-49) and a possible EphB2-SAM oligomer (Thanos, C. D., Goodwill, K. E., and Bowie, J. U. (1999) Science 283, 833-836) both revealed large interfaces comprising an exchange of N-terminal peptide arms. Within the arm, a conserved hydrophobic residue (Tyr-8 in the EphB2-SAM structure or Phe-910 in the EphA4-SAM structure) is anchored into a hydrophobic cleft on a neighboring molecule. Here we have solved a new crystal form of the human EphB2-SAM domain that has the same overall SAM domain fold yet has no substantial intermolecular contacts. In the new structure, the N-terminal peptide arm of the EphB2-SAM domain protrudes out from the core of the molecule, leaving both the arm (including Tyr-8) and the hydrophobic cleft solvent-exposed. To verify that Tyr-8 is solvent-exposed in solution, we made a Tyr-8 to Ala-8 mutation and found that the EphB2-SAM domain structure and stability were only slightly altered. These results suggest that Tyr-8 is not part of the hydrophobic core of the EphB2-SAM domain and is conserved for functional reasons. Cystallographic evidence suggests a possible role for the N-terminal arm in oligomerization. In the absence of a direct demonstration of biological relevance, however, the functional role of the N-terminal arm remains an open question.     

The structure of pyruvate kinase from Leishmania mexicana reveals details of the allosteric transition and unusual effector specificity.

Glycolysis occupies a central role in cellular metabolism, and is of particular importance for the catabolic production of ATP in protozoan parasites such as Leishmania and Trypanosoma. In these organisms pyruvate kinase plays a key regulatory role, and is unique in responding to fructose 2,6-bisphosphate as allosteric activator. The determination of the first eukaryotic pyruvate kinase crystal structure in the T-state is reported. A comparison of the leishmania and yeast R-state enzymes reveals fewer differences than the previous comparison of Escherichia coli T-state and rabbit muscle non-allosteric enzymes. Structural changes related to the allosteric transition can therefore be distinguished from those that are a consequence of the inherent wide structural divergence between bacterial and mammalian proteins. The allosteric transition involves significant changes in a tightly packed array of eight alpha helices at the interface near the catalytic site. At the other interface the allosteric transition appears to be accompanied by the bending of a ten-stranded intersubunit beta sheet adjacent to the effector site. Helix Calpha1 makes contacts to the N-terminal helical domain and bridges both interfaces. A comparison of the effector sites of the leishmania and yeast enzymes reveals the structural basis for the different effector specificity. Two loops comprising residues 443-453 and 480-489 adopt very different conformations in the two enzymes, and Lys453 and His480 that are a feature of trypanosomatid enzymes provide probable ligands for the 2-phospho group of the effector molecule. These differences offer an opportunity for the design of drugs that would bind to the trypanosomatid enzymes but not to those of the mammalian host.     

Genotype and diet effects in lean and obese Zucker rats fed either safflower or coconut oil diets

Previously we reported that suckling lean heterozygous (FA/fa) Zucker rats had a number of adipose tissue measurements intermediate between those of homozygous lean (FA/FA) and obese (fa/fa) rats. However, in young adult male rats maintained on a low-fat diet, these differences were no longer apparent (i.e., values for the two lean genotypes were similar). In the present study we determined whether the heterozygous effect of the "fa" gene was dependent on the consumption of a high-fat diet. Mother rats were fed high-fat diets containing either safflower (SOD) or coconut (COD) oil throughout mating and lactation. Homozygous lean male and female rats were bred, as well as obese male and lean heterozygous female rats. Suckling rats were studied at 17 days of age. Additional male rats were maintained on the same diet as their mothers until 11-12 weeks of age. Obese suckling rats had higher body weights than lean pups. Inguinal fat pad weights and pad-to-body weight ratios followed the pattern of obese greater than lean (FA/fa) pups that were greater than lean (FA/FA) pups. A similar relationship was found for adipose tissue lipogenic enzyme activities. At 11-12 weeks of age, measurements followed the general pattern of obese rats having greater values than lean rats (i.e., FA/fa = FA/FA). SOD-fa/fa rats had higher hepatic lipogenic enzyme activities than COD-fa/fa rats. In addition, SOD rats had higher fat cell numbers than COD rats. These results suggest that specific fatty acids can alter adipocyte proliferation and/or differentiation in vivo. In addition, there appears to be a defect of fatty acid regulation in livers of genetically obese rats. The heterozygous effect of the "fa" gene in suckling Zucker rats was confirmed. However, high-fat feeding did not result in a heterozygous effect in young adult lean male rats. We will next evaluate the role of sex on this effect.     

Orchid biogeography and factors associated with rarity in a biodiversity hotspot,the Southwest Australian Floristic Region

Aim The causes of orchid diversification and intrinsic rarity are poorly resolved. The Orchidaceae of the Southwest Australian Floristic Region use a diversity of pollination strategies and sites of mycorrhizal infection, and occupy a diversity of habitats. We combined a biogeographic analysis with analysis of factors associated with rarity to establish: (1) the landscape features correlated with taxon turnover and speciation, and (2) the possible role in taxon rarity of geographic region, pollination strategy, edaphic habitat and site of mycorrhizal infection. Location Southwest Australian Floristic Region. Methods The distributions of 407 orchid taxa (species and subspecies) were mapped at the quarter‐degree scale using 13,267 collections in the Western Australian Herbarium. This database was used to map taxon richness, for a biogeographic analysis and to quantify rarity of taxa. Using herbarium records, rarity was expressed as mean abundance, mean distribution and incidence of rarity based on abundance and distribution for each genus. We tested for differences in rarity of species between pollination strategies, edaphic habitats and sites of mycorrhizal infection. Results Taxon richness was highest in the High Rainfall Province. Biogeographic provincial boundaries for orchids were aligned with rainfall, while district boundaries tended to follow geological formations. When rarity was defined as either low abundance or small distribution, the greatest number of rare taxa occurred in areas of high taxon richness and naturally fragmented edaphic environments. For both abundance and distributional extent, sexual deception had a significantly higher incidence of rarity than food‐rewarding taxa. There was no significant difference in rarity with site of mycorrhizal infection. Main conclusions While large‐scale edaphic and climatic variation are correlated with orchid taxon turnover and speciation in a similar fashion to the flora in general, the processes responsible for patterns of diversity may differ. Fragmented edaphic environments appear to be associated with a higher incidence of rare species due to limited dispersal/colonization opportunities or radiations of taxa in allopatry. The high incidence of rarity in sexually deceptive taxa could be due to either low fruit set or the risk of specializing on a single pollinator species.     

Indicator microbes correlate with pathogenic bacteria, yeasts and helminthes in sand at a subtropical recreational beach site

Aims: Research into the relationship between pathogens, faecal indicator microbes and environmental factors in beach sand has been limited, yet vital to the understanding of the microbial relationship between sand and the water column and to the improvement of criteria for better human health protection at beaches. The objectives of this study were to evaluate the presence and distribution of pathogens in various zones of beach sand (subtidal, intertidal and supratidal) and to assess their relationship with environmental parameters and indicator microbes at a non‐point source subtropical marine beach. Methods and Results: In this exploratory study in subtropical Miami (Florida, USA), beach sand samples were collected and analysed over the course of 6 days for several pathogens, microbial source tracking markers and indicator microbes. An inverse correlation between moisture content and most indicator microbes was found. Significant associations were identified between some indicator microbes and pathogens (such as nematode larvae and yeasts in the genus Candida), which are from classes of microbes that are rarely evaluated in the context of recreational beach use. Conclusions: Results indicate that indicator microbes may predict the presence of some of the pathogens, in particular helminthes, yeasts and the bacterial pathogen Staphylococcus aureus including methicillin‐resistant forms. Indicator microbes may thus be useful for monitoring beach sand and water quality at non‐point source beaches. Significance and Impact of the Study: The presence of both indicator microbes and pathogens in beach sand provides one possible explanation for human health effects reported at non‐point sources beaches.