Improbable but true: the invasive inbreeding ambrosia beetle Xylosandrus morigerus has generalist genotypes

The wide distribution and dominance of invasive inbreeding species in many forest ecosystems seems paradoxical in face of their limited genetic variation. Successful establishment of invasive species in new areas is nevertheless facilitated by clonal reproduction: parthenogenesis, regular self-fertilization, and regular inbreeding. The success of clonal lineages in variable environments has been explained by two models, the frozen niche variation (FNV) model and the general-purpose genotype (GPG) model. We tested these models on a widely distributed forest pest that has been recently established in Costa Rica-the sibling-mating ambrosia beetle Xylosandrus morigerus. Two deeply diverged mitochondrial haplotypes coexist at multiple sites in Costa Rica. We find that these two haplotypes do not differ in their associations with ecological factors. Overall the two haplotypes showed complete overlap in their resource utilization; both genotypes have broad niches, supporting the GPG model. Thus, probable or not, our findings suggest that X. morigerus is a true ecological generalist. Clonal aspects of reproduction coupled with broad niches are doubtless important factors in the successful colonization of new habitats in distant regions.     

Expanding the Cyanuric Acid Hydrolase Protein Family to the Fungal Kingdom

The known enzymes that open the s-triazine ring, the cyanuric acid hydrolases, have been confined almost exclusively to the kingdom Bacteria and are all homologous members of the rare cyanuric acid hydrolase/barbiturase protein family. In the present study, a filamentous fungus, Sarocladium sp. strain CA, was isolated from soil by enrichment culturing using cyanuric acid as the sole source of nitrogen. A reverse-genetic approach identified a fungal cyanuric acid hydrolase gene composed of two exons and one intron. The translated spliced sequence was 39 to 53% identical to previously characterized bacterial cyanuric acid hydrolases. The sequence was used to generate a gene optimized for expression in Escherichia coli and encoding an N-terminally histidine-tagged protein. The protein was purified by nickel affinity and anion-exchange chromatography. The purified protein was shown by ¹³C nuclear magnetic resonance (¹³C-NMR) to produce carboxybiuret as the product, which spontaneously decarboxylated to yield biuret and carbon dioxide. The protein was very narrow in substrate specificity, showing activity only with cyanuric acid and N-methyl cyanuric acid. Barbituric acid was an inhibitor of enzyme activity. Sequence analysis identified genes with introns in other fungi from the Ascomycota that, if spliced, are predicted to encode proteins with cyanuric acid hydrolase activity. The Ascomycota cyanuric acid hydrolase homologs are most closely related to cyanuric acid hydrolases from Actinobacteria.     

Biotransformation of linear alkylbenzene sulfonate (LAS) by Phanerochaete chrysosporium: oxidation of alkyl side-chain

The white rot fungus Phanerochaete chrysosporium, which generally mineralizes substituted aromatics to CO₂, transformed linear alkylbenzene sulfonate (LAS) surfactants mainly at their alkyl side chain. Degradation of LAS was evidenced by a zone of clearing on LAS-containing agar plates and colorimetric analysis of liquid cultures. Disappearance of LAS was virtually complete within 10 days in low nitrogen (2.4 mM N), high nitrogen (24 mM N) and malt extract (ME) liquid media. After 5 days of incubation in ME medium, transformation of LAS was complete at concentrations4 mg l^-1, but decreased at higher concentrations. The LAS degradation was not dependent on lignin peroxidases (LiPs) and manganese-dependent peroxidases (MnPs). Mineralization of¹⁴C-ring-LAS to ¹⁴CO₂ by P. chrysosporium was <1% regardless of the culture conditions used. Thin layer chromatography and mass spectral analyses indicated that P. chrysosporium transformed LAS to sulfophenyl carboxylates (SPCs) through oxidative shortening of the alkyl side-chains. While LAS disappearance in the cultures was not dependent on LiPs and MnPs, transformation of the parent LAS moieties to SPCs was more extensive in low N medium that favors expression of these enzymes. The SPCs produced in LN cultures were shorter in chain-length than those produced in ME cultures. Also there was a notable shift in the relative abundance of odd and even chain length metabolites compared to the starting LAS particularly in the low N cultures suggesting the possible involvement of processes other than or in addition to-oxidation in the chain-shortening process.     

The effects of carbon monoxide and hypoxic hypoxia on amine-containing cells in the tracheal epithelium of young rabbits

Summary Endogenously fluorescent, singly occurring, amine-containing cells in tracheal epithelium were examined in 3-, 10-, and 28-day-old rabbits. These cells are pyramidal in shape with the apex projected toward the tracheal lumen. The cytoplasm exhibits a yellow fluorescence which is predominantly supranuclear. Occasional, infranuclear, fluorescent cytoplasmic processes project from the cells. The numbers of fluorescent cells per unit length of trachea increase with age. Acute exposure of 10-day-old rabbits to 13% O₂ decreases the number of detectable fluorescent cells in the trachea compared to controls exposed to room air. Similarly, exposure to 750 ppm carbon monoxide decreases the number of fluorescent epithelial cells appearing in tracheas of 10- and 28-day-old rabbits. These results suggest that the amine-containing epithelial cells of the trachea respond to tissue hypoxia and that decreased airway pO₂ is not necessary to elicit a response.Supported by a grant from The Council for Tobacco Research, U.S.A., Inc. We are grateful to Margaret Hogan and Scott Pine for technical assistance     

The HSPGs Syndecan and Dallylike bind the receptor phosphatase LAR and exert distinct effects on synaptic development

The formation and plasticity of synaptic connections rely on regulatory interactions between pre- and postsynaptic cells. We show that the Drosophila heparan sulfate proteoglycans (HSPGs) Syndecan (Sdc) and Dallylike (Dlp) are synaptic proteins necessary to control distinct aspects of synaptic biology. Sdc promotes the growth of presynaptic terminals, whereas Dlp regulates active zone form and function. Both Sdc and Dlp bind at high affinity to the protein tyrosine phosphatase LAR, a conserved receptor that controls both NMJ growth and active zone morphogenesis. These data and double mutant assays showing a requirement of LAR for actions of both HSPGs lead to a model in which presynaptic LAR is under complex control, with Sdc promoting and Dlp inhibiting LAR in order to control synapse morphogenesis and function.