Changes in phytoplankton ecophysiology across a coastal upwelling front

The abundance, taxonomic composition and patterns of macromolecularsynthesis of phytoplankton were determined across an upwelling-inducedthermal front in the central Cantabrian Sea (southern Bay ofBiscay) during July 1993. Enhanced levels of phytoplankton biomass,diatom abundance and photosynthetic rate were measured on thecoastal side of the front. Relative carbon (C) incorporationinto proteins increased noticeably on the oceanic side, takingvalues of up to 64%, whereas changes in the relative C incorporationinto lipids and low-molecular-weight metabolites followed anopposite trend. Phytoplankton cells on the oceanic side of thefront were adapted to the prevailing growth-limiting conditionsby maintaining the synthesis of functionally essential molecules—proteins—ratherthan the synthesis of storage compounds. As a result, the carbonto nitrogen uptake ratio varied from {small tilde}5.7 in offshorewaters to 8.0 in the nearshore region. Our results suggest thatthe taxonomic and physiological changes in phytoplankton assemblagesas a response to upwelling may result in an increase in thesynthesis of organic C relative to the upward flux of nitrate.     

Nest building by lowland gorillas in the Lopé Reserve,Gabon: Environmental influences and implications for censusing

We analyzed data from 373 fresh nest-sites (containing 2435 nests) of lowland gorillas (Gorilla g. gorilla)during a 4-year period in the Lopé Reserve, Gabon, to determine whether the observed variability in nest building was due to environmental influences. We recognized and defined seven types of nest in terms of the degree of construction and the raw materials used. Overall, nests built on the ground from herbaceous plants are the most common type (40%), followed by tree nests (35%). Frequencies of the different nest-types vary significantly between eight habitat-types. In habitat-types with high densities of understory herbs, ground nests predominated, but when herbs were rare, the majority of nests were in trees. A general preference for sleeping in herbaceous ground nests is indicated since trees are abundant in all habitat-types, except savanna. The frequency of nesting in trees shows a significant positive correlation with rainfall, but effects of climate are confounded by seasonal variation in use of different habitat-types. When elephants were attracted to the same localized food sources as gorillas, many tree nests were built even when herbs were available. We conclude that different nest-types reflect a variety of solutions to maximize comfort, depending on available raw materials and the probability of rainfall or disturbance by elephants or both factors. Nests are a powerful tool for population censuses and demographic studies of great apes, but problems exist in interpreting data on lowland gorilla nests. Results from this analysis show that only a third of nest-sites accurately reflects group size (of weaned individuals) and that 26% of all gorilla nest-sites could be mistaken for those of chimpanzees, as all nests, or all those visible from a transect, were in trees. Gorilla nests at Lopé were nonrandomly distributed with respect to habitat-types, and nest construction varied seasonally, thereby introducing sources of bias to transect nest counts. We discuss these problems and ones related to assessing the decay rate of nest-sites and make recommendations relevant to census work.     

The Drosophila insulin receptor homolog: a gene essential for embryonic development encodes two receptor isoforms with different signaling potential.

We report the cloning and primary structure of the Drosophila insulin receptor gene (inr), functional expression of the predicted polypeptide, and the isolation of mutations in the inr locus. Our data indicate that the structure and processing of the Drosophila insulin proreceptor are somewhat different from those of the mammalian insulin and IGF 1 receptor precursors. The INR proreceptor (M(r) 280 kDa) is processed proteolytically to generate an insulin-binding alpha subunit (M(r) 120 kDa) and a beta subunit (M(r) 170 kDa) with protein tyrosine kinase domain. The INR beta 170 subunit contains a novel domain at the carboxyterminal side of the tyrosine kinase, in the form of a 60 kDa extension which contains multiple potential tyrosine autophosphorylation sites. This 60 kDa C-terminal domain undergoes cell-specific proteolytic cleavage which leads to the generation of a total of four polypeptides (alpha 120, beta 170, beta 90 and a free 60 kDa C-terminus) from the inr gene. These subunits assemble into mature INR receptors with the structures alpha 2(beta 170)2 or alpha 2(beta 90)2. Mammalian insulin stimulates tyrosine phosphorylation of both types of beta subunits, which in turn allows the beta 170, but not the beta 90 subunit, to bind directly to p85 SH2 domains of PI-3 kinase. It is likely that the two different isoforms of INR have different signaling potentials. Finally, we show that loss of function mutations in the inr gene, induced by either a P-element insertion occurring within the predicted ORF, or by ethylmethane sulfonate treatment, render pleiotropic recessive phenotypes that lead to embryonic lethality. The activity of inr appears to be required in the embryonic epidermis and nervous system among others, since development of the cuticle, as well as the peripheral and central nervous systems are affected by inr mutations.     

Quantitative analysis of biofilm thickness variability

The thickness variability of biofilms of Pseudomonas aeruginosa, Klebsiella pneumoniae, and the binary population combination of these two species was quantified. The experimental method involved cryoembedding biofilms with a commercial tissue embedding agent, sectioning, and applying image analysis to construct thickness profiles along linear transects (up to 1 cm in length) across the substratum. Biofilms embedded and sectioned by this method were locally as thin as a single cell attached to the surface (<5 mum) and as thick as 1000 mum. Week-old biofilms of three different species compositions displayed distinct structural features as indicated by their mean thicknesses and by a roughness coefficient. Monopopulation biofilms of P. aeruginosa (29 mum mean thickness) or K. pneumoniae (100 mum mean thickness) were thinner than the binary population biofilm (400 mum mean thickness). A roughness coefficient developed in this investigation corroborated the qualitative visual characterization of P. aeruginosa biofilms as relatively uniformly thick (mean roughness coefficient 0.15), K. pneumoniae biofilms as patchy (mean roughness coefficient 1.14), and the binary population biofilm as intermediate (mean roughness coefficient 0.26). Whereas P. aeruginosa and binary population biofilms covered the substratum completely, significant areas of essentially bare substratum were apparent in K. pneumoniae biofilms. The patchiness of K. pneumoniae biofilms may be due to the fact that this organism is nonmotile. A spatial correlation analysis of the thickness data indicated that thickness measurements were still correlated even when separated by distances that exceeded the mean biofilm thickness. Cell aggregates, some of them hundreds of microns in size, were observed in the effluent of K. pneumoniae and binary population biofilm reactors. Measurements of thickness variability and other observations reported in this article provide a quantitative basis for analysis of microscale structural heterogeneity of biofilms. (c) 1995 John Wiley & Sons, Inc.     

The serum response factor nuclear localization signal: general implications for cyclic AMP-dependent protein kinase activity in control of nuclear translocation.

We have identified a basic sequence in the N-terminal region of the 67-kDa serum response factor (p67SRF or SRF) responsible for its nuclear localization. A peptide containing this nuclear localization signal (NLS) translocates rabbit immunoglobulin G (IgG) into the nucleus as efficiently as a peptide encoding the simian virus 40 NLS. This effect is abolished by substituting any two of the four basic residues in this NLS. Overexpression of a modified form of SRF in which these basic residues have been mutated confirms the absolute requirement for this sequence, and not the other basic amino acid sequences adjacent to it, in the nuclear localization of SRF. Since this NLS is in close proximity to potential phosphorylation sites for the cAMP-dependent protein kinase (A-kinase), we further investigated if A-kinase plays a role in the nuclear location of SRF. The nuclear transport of SRF proteins requires basal A-kinase activity, since inhibition of A-kinase by using either the specific inhibitory peptide PKIm or type II regulatory subunits (RII) completely prevents the nuclear localization of plasmid-expressed tagged SRF or an SRF-NLS-IgG conjugate. Direct phosphorylation of SRF by A-kinase can be discounted in this effect, since mutation of the putative phosphorylation sites in either the NLS peptide or the encoded full-length SRF protein had no effect on nuclear transport of the mutants. Finally, in support of an implication of A-kinase-dependent phosphorylation in a more general mechanism affecting nuclear import, we show that the nuclear transport of a simian virus 40-NLS-conjugated IgG or purified cyclin A protein is also blocked by inhibition of A-kinase, even though neither contains any potential sites for phosphorylation by A-kinase or can be phosphorylated by A-kinase in vitro.     

Incidence of heavy metals in the mangrove flora and sediments in Kerala, India

The mangroves of Kerala on the south-west coast of India are fast disappearing due to land reclamation and other anthropogenic disturbances. There are very few ecosystem level studies made in these much threatened biotopes in Kerala. The present study involves the measurement of heavy metals in the mangrove flora and sediments of three mangrove habitats along the Kerala coast. Sampling was carried out for a period of one year at bi-monthly intervals, with concentrations of Fe, Mn, Cu,Zn,Pb and Co analysed using atomic absorption spectrophotometry. An appreciable variation was observed in metal concentrations indifferent mangrove species. Cu, Zn and Pb were found to be in higher concentrations in Avicennia officinalis whereas higher levels of Fe, Mn and Co were observed in the species Barringtonia racemosa. The analysis of heavy metals indicated a high level of metal pollutants such as Fe, Cu, Zn and Pb in the mangrove habitats of Quilon and Veli compared to the relatively uncontaminated areas of Kumarakom. This revised version was published online in August 2006 with corrections to the Cover Date.     

Isolation of cDNA and genomic DNA clones encoding type II collagen.

A cDNA library constructed from total chick embryo RNA was screened with an enriched fraction of type II collagen mRNA. Two overlapping cDNA clones were characterized and shown to encode the COOH propeptide of type II collagen. In addition, a type II collagen clone was isolated from a Charon 4A library of chick genomic fragments. Definitive identification of the clones was based on DNA sequence analysis. The 3' end of the type II collagen gene appears to be similar to that of other interstitial collagen genes. Northern hybridization data indicates that there is a marked decrease in type II collagen mRNA levels in chondrocytes treated with the dedifferentiating agent 5-bromodeoxyuridine. The major type II collagen mRNA species is 5300 bases long, similar to that of other interstitial collagen RNAs.