The impact of resource limitation and the phenology of parasitoid attack on the duration of insect herbivore outbreaks

Fluctuations in resource quality and quantity, and changes in mortality due to predators and parasites are thought to be of prime importance in the regular fluctuations of forest insects. We examine how food limitation and parasitoids with different phenologies of attack regulate the population cycles of insect hosts. Our analysis of the limit cycle of a model with a biologically realistic form of density dependence in the host yields two novel predictions. First, outbreaks will typically last for only 2 generations after parasitoids begin to reduce the host population below the maximum density. Second, host growth rate is important in determining cycle length only when parasitoids attack before the impacts of resource limitation affect the host. The robustness of these predictions are tested using a more general form of density dependence in the host, revealing that our predictions are valid as long as density dependence in the host is not too overcompensatory.     

Isolation of antibiotics turbomycin a and B from a metagenomic library of soil microbial DNA

To access the genetic and biochemical potential of soil microorganisms by culture-independent methods, a 24,546-member library in Escherichia coli with DNA extracted directly from soil had previously been constructed (M. R. Rondon, P. R. August, A. D. Bettermann, S. F. Brady, T. H. Grossman, M. R. Liles, K. A. Loiacono, B. A. Lynch, I. A. MacNeil, M. S. Osburne, J. Clardy, J. Handelsman, and R. M. Goodman, Appl. Environ. Microbiol. 66:2541-2547, 2000). Three clones, P57G4, P89C8, and P214D2, produced colonies with a dark brown melanin-like color. We fractionated the culture supernatant of P57G4 to identify the pigmented compound or compounds. Methanol extracts of the acid precipitate from the culture supernatant contained a red and an orange pigment. Structural analysis revealed that these were triaryl cations, designated turbomycin A and turbomycin B, respectively; both exhibited broad-spectrum antibiotic activity against gram-negative and gram-positive organisms. Mutagenesis, subcloning, and sequence analysis of the 25-kb insert in P57G4 demonstrated that a single open reading frame was necessary and sufficient to confer production of the brown, orange, and red pigments on E. coli; the predicted product of this sequence shares extensive sequence similarity with members of the 4-hydroxyphenylpyruvate dioxygenase (4HPPD) family of enzymes. Another member of the same family of genes, lly, which is required for production of the hemolytic pigment in Legionella pneumophila, also conferred production of turbomycin A and B on E. coli. We further demonstrated that turbomycin A and turbomycin B are produced from the interaction of indole, normally secreted by E. coli, with homogentisic acid synthesized by the 4HPPD gene products. The results demonstrate successful heterologous expression of DNA extracted directly from soil as a means to access previously uncharacterized small organic compounds, serving as an example of a chimeric pathway for the generation of novel chemical structures.     

Biodiversity of the bacterial flora on the surface of a smear cheese

The bacteria on the surface of a farmhouse smear-ripened cheese at four stages of ripening (4, 16, 23, and 37 days) from inoculated (i.e., deliberately inoculated with Brevibacterium linens BL2) and noninoculated (not deliberately inoculated with B. linens BL2) cheese were investigated. The results show that, contrary to accepted belief, B. linens is not a significant member of the surface flora of smear cheese and no microbial succession of species occurred during the ripening of the cheeses. Of 400 isolates made, 390 were lactate-utilizing coryneforms and 10 were coagulase-negative Staphylococcus spp. A detailed analysis of the coryneforms was undertaken using phenotypic analysis, molecular fingerprinting, chemotaxonomic techniques, and 16S rRNA gene sequencing. DNA banding profiles (ramdom amplified polymorphic DNA [RAPD]-PCR) of all the coryneform isolates showed large numbers of clusters. However, pulsed-field gel electrophoresis (PFGE) of the isolates from the cheeses showed that all isolates within a cluster and in many contiguous clusters were the same. The inoculated and noninoculated cheeses were dominated by single clones of novel species of Corynebacterium casei (50.2% of isolates), Corynebacterium mooreparkense (26% of isolates), and Microbacterium gubbeenense (12.8% of isolates). In addition, five of the isolates from the inoculated cheese were Corynebacterium flavescens. Thirty-seven strains were not identified but many had similar PFGE patterns, indicating that they were the same species. C. mooreparkense and C. casei grew at pH values below 4.9 in the presence of 8% NaCl, while M. gubbeenense did not grow below pH 5.8 in the presence of 5 to 10% NaCl. B. linens BL2 was not recovered from the inoculated cheese because it was inhibited by all the Staphylococcus isolates and many of the coryneforms. It was concluded that within a particular batch of cheese there was significant bacterial diversity in the microflora on the surface.     

Pediatric grand rounds: a tribute to Norman J. Siegel, M.D

At ceremonies held in Baltimore Maryland on May, 4, 2002, Dr. Howard A Pearson, Professor of Pediatrics, was awarded the John A. Howland award of the American Pediatric Society, probably the most prestigious award of American Pediatrics. Dr. Pearson had been nominated for the award by Dr. Norman Siegel. The Department of Pediatrics Grand Rounds on Wednesday noon, October 26, 2002 was originally scheduled as a repetition of the presentation by Dr. Siegel and the acceptance by Dr. Pearson for those who could not be in Baltimore. However; in a number of meetings, unknown to Dr. Siegel, it was unanimously decided that it would be very appropriate to instead honor him as he stepped down from his position as Vice- and Interim Chairman of Pediatrics, and to formally thank him for his long and faithful service to the Department of Pediatrics, the Yale University School of Medicine, and the Yale New Haven Hospital.     

Hantavirus pulmonary syndrome in Uberaba,Minas Gerais,Brazil

This report describes the epidemiological and clinical-evolutive characteristics of eight patients with hantavirus pulmonary syndrome (HPS) in Uberaba, Minas Gerais, Brazil. A positive history of contact with rodents was present in 100% of the cases. The time between the onset of symptoms and hospital care was, on average, 3.6 days. All patients showed clinical and laboratory findings suggestive of HPS. Elevated urea and creatinine levels were observed in 6 (75%) cases, PO2 was < 60 mmHg in 100% of the cases, and a chest X-ray demonstrated a bilateral interstitial-alveolar infiltrate. The diagnosis was confirmed by the detection of IgM antibodies against Sin Nombre virus by ELISA. Three patients died as a direct consequence of HPS.     

Normal conjunctival flora in the North American opossum (Didelphis virginiana) and raccoon (Procyon lotor)

We documented the normal conjunctival bacterial flora from 17 opossums (Didelphis virginiana) and 10 raccoons (Procyon lotor) trapped in Manhattan, Kansas (USA) from November 1999 to January 2000. Both raccoons and opossums were free of apparent ocular disease. The inferior conjunctival sacs of each animal were swabbed for aerobic bacterial and Mycoplasma culture and polymerase chain reaction (PCR) for Mycoplasma and Chlamydia detection. All conjunctival samples were positive for one or more species of aerobic bacteria. The most common isolate from opossums was Staphylococcus spp. Other isolates included Streptococcus spp., Bacillus spp., Corynebacterium spp., and Enterococcus faecalis. The most common isolates in raccoons was Bacillus spp. Other isolates included Streptococcus spp., Staphylococcus spp., non-hemolytic Escherichia coli, and Enterococcus faecalis. Mycoplasma culture was negative in samples from opossums and raccoons. Evidence of Mycoplasma and Chlamydia presence was detected by PCR.     

Helminth community structure in an expanding white-winged dove (Zenaida asiatica asiatica) population

Helminth communities of 171 fledged white-winged doves (Zenaida asiatica asiatica) from the expanding eastern population in Texas (USA) were examined from hosts collected 11 June to 19 September 1997 within their historical range, new breeding periphery, and an intermediate area. Eleven helminth species, representing 435 individuals, were found. Helminths occurred in three microhabitats, of which the small intestine was the most commonly occupied. Nematodes dominated numerically (76% of total worms), followed by cestodes (17%), and trematodes (7%). Infracommunities were species-poor; the most complex infracommunity consisted of three helminth species, which occurred in three host individuals, followed by two species that occurred in 13 hosts. The remaining 155 doves had one (70) or no (85) species. The overall helminth component community was species-poor and was dominated by Ascaridia columbae which occurred in 26% of the white-winged doves and accounted for 65% of all helminth individuals. Prevalence and abundance of A. columbae varied by geographic region and host age, but not by host sex. Helminth component communities varied by geographic region, host age, and host sex. These differences were primarily attributable to unique occurrences of uncommon species within specific host subpopulations. Results suggest that the white-winged doves' multimodal regional abundance pattern, sympatry with other columbids, and granivorous diet may be more important in shaping helminth community structure than the influences often associated with geographic range expansion.     

Extinction dynamics in mainland-island metapopulations: an N-patch stochastic model

A generalization of the well-known Levins’ model of metapopulations is studied. The generalization consists of (i) the introduction of immigration from a mainland, and (ii) assuming the dynamics is stochastic, rather than deterministic. A master equation, for the probability that n of the patches are occupied, is derived and the stationary probability P _s (n), together with the mean and higher moments in the stationary state, determined. The time-dependence of the probability distribution is also studied: through a Gaussian approximation for general n when the boundary at n = 0 has little effect, and by calculating P(0, t), the probability that no patches are occupied at time t, by using a linearization procedure. These analytic calculations are supplemented by carrying out numerical solutions of the master equation and simulations of the stochastic process. The various approaches are in very good agreement with each other. This allows us to use the forms for P _s 0) and P(0, t) in the linearization approximation as a basis for calculating the mean time for a metapopulation to become extinct. We give an analytical expression for the mean time to extinction derived within a mean field approach. We devise a simple method to apply our mean field approach even to complex patch networks in realistic model metapopulations. After studying two spatially extended versions of this nonspatial metapopulation model—a lattice metapopulation model and a spatially realistic model—we conclude that our analytical formula for the mean extinction time is generally applicable to those metapopulations which are really endangered, where extinction dynamics dominates over local colonization processes. The time evolution and, in particular, the scope of our analytical results, are studied by comparing these different models with the analytical approach for various values of the parameters: the rates of immigration from the mainland, the rates of colonization and extinction, and the number of patches making up the metapopulation.     

How to eat something bigger than your head

Characterization of the mechanisms underlying various types of muscular dystrophy has been an outstanding triumph of molecular biology. Increasing clarification of the aberrant cellular processes responsible for these conditions may ultimately permit the development of effective means for molecular intervention, allowing correction of the abnormal cellular physiology that results in the dystrophic phenotype.     

Cid13 is a cytoplasmic poly(A) polymerase that regulates ribonucleotide reductase mRNA

Fission yeast Cid13 and budding yeast Trf4/5 are members of a newly identified nucleotidyltransferase family conserved from yeast to man. Trf4/5 are thought to be essential DNA polymerases. We report that Cid13 is a poly(A) polymerase. Unlike conventional poly(A) polymerases, which act in the nucleus and indiscriminately polyadenylate all mRNA, Cid13 is a cytoplasmic enzyme that specifically targets suc22 mRNA that encodes a subunit of ribonucleotide reductase (RNR). cid13 mutants have reduced dNTP pools and are sensitive to hydroxyurea, an RNR inhibitor. We propose that Cid13 defines a cytoplasmic form of poly(A) polymerase important for DNA replication and genome maintenance.