Management of invasive plants through ecological resistance

Despite debates on the real impact of plant invasion on native biodiversity, there remain many situations where exotic invasive plants must be managed and habitats restored. Restoration practices that build on plant community assembly principles could be useful to delay or prevent re-invasion after control, but there are still few syntheses of the biodiversity theory, ecological mechanisms and experimental evidence relevant to invasive plant management, possibly delaying applications. To provide such a synthesis, we review current knowledge on three key determinants of invasion success: biotic resistance, abiotic constraints, and propagule pressure. We elaborate on the ecological mechanisms at play for each determinant and emphasize, using case studies, their relevance for invasive plant management and ecological restoration. We find evidence that restoring a plant cover can enhance invasion resistance, but the challenge for both research and field applications is to understand how multiple determinants interact in relation to species traits in the fields. Failure to recognize these interactions and their effect on community assembly processes may explain some of the mixed species responses observed. While we need control and restoration case studies with local species at different sites, the development of a coherent, dynamic and adaptive framework around biotic/ecological resistance will have to go beyond the idiosyncrasy of the many species and systems being tested. Emphasizing the functional diversity of the restored community seems a promising approach when facing potentially multiple invaders and/or fluctuating abiotic conditions.     

Effect of plant and artificial aeration on solids accumulation and biological activities in constructed wetlands

In constructed wetlands, solids accumulation may have two consequences with opposing effects on treatment efficiency: it decreases the longevity by reducing void space and it enhances biological activity by favoring biofilm development. The goal of our study was to estimate the effect of plants (presence and species) and artificial aeration on solids accumulation (volatile and inorganic). The horizontal and vertical distribution of solids was sampled using solids traps in 12 constructed wetland mesocosms (5 years old). Microbial density and activity were estimated in the biological fraction of the sampled solids. The effect of plant presence reduced accumulated solids by 26% and sulphide content by 50% sulphide content. There was more solids accumulation in Typha angustifolia units than in Phragmites australis. Also, T. angustifolia generated more biological activities at the surface and close to the inlet while conditions were more homogeneous throughout P. australis units. Aeration (1) stimulated biofilm development at the inlet of planted beds, (2) seemed to reduce mineral matter accumulation and (3) generated the same pattern of activities in planted beds enabling to reach a total nitrogen removal rate of up to 0.65 g N m^?2 d^?1.     

Neonatal exposure to oestrogens alters the protein profiles and gene expression in the genital tract of adult male mice.

After neonatal administration of supraphysiological doses of oestradiol, the concentration of tissue proteins, in adult mice, was significantly reduced by 39, 45 and 56% in epididymis, vas deferens and seminal vesicle respectively. The protein profiles showed persistent alterations. In epididymis, 4 protein bands were differentially increased (14.4, 43 and 67 kDa) or reduced (24 kDa) in oestrogenized males. In vas deferens, 4 proteins were increased (14.4, 49,67 and 76 kDa) and one (34 kDa) virtually absent. In seminal vesicle, about 20 proteins of varying molecular weights (12-140 kDa) were differentially increased or decreased. Testosterone substitution, at adulthood, was unable to reverse these effects. Treatments with oestradiol during adult life induced persistent alterations in the protein profiles of the 3 organs but, in contrast to neonatal treatment, these alterations could be reversed by androgen therapy. A cDNA library has been constructed with RNA prepared from adult seminal vesicle and screened by differential hybridization. Neonatal oestrogenization strongly reduced the abundance of some mRNA species. Eleven recombinants containing putative oestrogen-sensitive sequences were isolated. Two of them, having an insert of about 500 base pairs, were used for dot-blot hybridization. Results showed that the two clones contained sequences which were differently regulated by androgens.     

Identification of bacteria in pasteurized zucchini purées stored at different temperatures and comparison with those found in other pasteurized vegetable purées

One hundred nineteen isolates from a commercial zucchini purée stored at 4, 10, and 20 to 25 degrees C were fingerprinted using repetitive sequence-based PCR (REP-PCR) and classified into 35 REP types. One representative isolate of each REP type was subsequently identified by API50CHB/20E profile and partial rrs gene sequence analysis. Nine REP types were misidentified by the API system. Strains were misidentified as being in the Bacillus circulans (group 2) API taxon or in taxa with a low number of positive API characters such as Brevibacillus brevis. A phylogenetic analysis pointed to one new species of Bacillus and three new species of Paenibacillus among the misidentified REP types. Bacterial components in zucchini purée were compared phenotypically with those obtained in previous work on broccoli, carrot, leek, potato, and split pea purées, based on simple matching coefficient and unweighted pair group method with averages cluster analysis. Out of 254 strains, 69 strains previously identified as B. circulans (group 2) or B. circulans/B. macerans/B. polymyxa were assigned to a new Paenibacillus taxon phylogenetically related to P. azotofixans. Storage conditions at 4 degrees C favored the development of "B. macroides/B. maroccanus" and Paenibacillus spp. in zucchini purées and Paenibacillus spp. in other purées. Storage conditions at 20 to 25 degrees C favored the development of B. subtilis group (B. licheniformis and B. subtilis) and B. cereus group strains. At 10 degrees C, Paenibacillus spp. were always present at high frequencies, whereas the occurrence of B. macroides/B. maroccanus (in zucchini purées), B. cereus, and B. pumilus varied with the experiment.     

Cloning, expression, and sequence conservation of pathogenesis-related gene transcripts of potato

Treatment of potato tuber disks with arachidonic acid elicits the accumulation of several mRNAs. cDNA clones corresponding to two of these mRNAs were isolated and characterized. Nucleotide sequence analysis reveals that both clones (pSTH-2 and pSTH-21) contain an open-reading frame coding for a 155-amino acid polypeptide. The polypeptides encoded by the two clones differ by only six amino acids and show a high degree of similarity with PR protein sequences from pea (approximately 42%) and parsley (approximately 37%). mRNAs corresponding to the two potato cDNA clones also accumulate in Solanum chacoense and in tomato following elicitor treatment. Maximum accumulation of the mRNAs corresponding to the two cDNA clones is reached 24 hr after elicitor treatment of the tuber disks. pSTH-2-related mRNAs also accumulate in tubers after wounding or treatment with eicosapentaenoic acid and are detected in potato and tomato leaves treated with a Phytophthora infestans mycelium homogenate. The presence of these conserved genes in species from three plant families and the similarity of their induction pattern suggest an important function during the plant defense response.     

Subcellular localization of 14-3-3 proteins in Toxoplasma gondii tachyzoites and evidence for a lipid raft-associated form

A polyclonal antibody was raised against a Toxoplasma gondii 14-3-3-gluthatione S-transferase fusion protein obtained by cloning a 14-3-3 cDNA sequence determined from the T. gondii database. This antibody specifically recognized T. gondii 14-3-3 without any cross-reaction with mammalian proteins. Immunofluorescence microscopy studies of the tachyzoites or the T. gondii-infected cells suggested cytosolic and membranous localizations of 14-3-3 protein. Different subcellular fractions were prepared for electrophoresis analysis and immunodetection. 14-3-3 proteins were found in the cytosol, the membrane fraction and Triton X-100-resistant membranes. Two 14-3-3 isoforms were detected. The major one was mainly cytoplasmic and to a lesser extent membrane-associated, whereas the minor isoform was associated with the detergent-resistant lipid rafts.     

Genetic and functional aspects of linoleate isomerase in Lactobacillus acidophilus

While the remarkable health effects of conjugated linoleic acid (CLA) catalyzed from α-linoleic acid by the enzyme linoleate isomerase (LI, EC 5.2.1.5) are well recognized, how widely this biochemical activity is present and the mechanisms of its regulation in lactic acid bacteria are unknown. Although certain strains of Lactobacillus acidophilus can enrich CLA in fermented dairy products, it is unknown if other strains share this capacity. Due to its immense economic importance, this work aimed to investigate genetic aspects of CLA production in L. acidophilus for the first time. The genomic DNA from industrial and type strains of L. acidophilus were subjected to PCR and immunoblot analyses using the putative LI gene of L. reuteri ATCC 55739 as probe. The CLA production ability was estimated by gas chromatography of the biomass extracts. The presumptive LI gene from L. acidophilus ATCC 832 was isolated and sequenced. The resulting sequence shared 71% identity with that of L. reuteri and at least 99% with reported sequences from other L. acidophilus strains. All the strains accumulated detectable levels of CLA and tested positive by PCR and immunoblotting. However, no apparent correlation was observed between the yields and the hybridization patterns. The results suggest that LI activity might be common among L. acidophilus and related species and provide a new tool for screening potential CLA producers.     

Glycans Flanking the Hypervariable Connecting Peptide between the A and B Strands of the V1/V2 Domain of HIV-1 gp120 Confer Resistance to Antibodies That Neutralize CRF01_AE Viruses

Understanding the molecular determinants of sensitivity and resistance to neutralizing antibodies is critical for the development of vaccines designed to prevent HIV infection. In this study, we used a genetic approach to characterize naturally occurring polymorphisms in the HIV envelope protein that conferred neutralization sensitivity or resistance. Libraries of closely related envelope genes, derived from virus quasi-species, were constructed from individuals infected with CRF01_AE viruses. The libraries were screened with plasma containing broadly neutralizing antibodies, and neutralization sensitive and resistant variants were selected for sequence analysis. In vitro mutagenesis allowed us to identify single amino acid changes in three individuals that conferred resistance to neutralization by these antibodies. All three mutations created N-linked glycosylation sites (two at N136 and one at N149) proximal to the hypervariable connecting peptide between the C-terminus of the A strand and the N-terminus of the B strand in the four-stranded V1/V2 domain β-sheet structure. Although N136 has previously been implicated in the binding of broadly neutralizing monoclonal antibodies, this glycosylation site appears to inhibit the binding of neutralizing antibodies in plasma from HIV-1 infected subjects. Previous studies have reported that the length of the V1/V2 domain in transmitted founder viruses is shorter and possesses fewer glycosylation sites compared to viruses isolated from chronic infections. Our results suggest that vaccine immunogens based on recombinant envelope proteins from clade CRF01_AE viruses might be improved by inclusion of envelope proteins that lack these glycosylation sites. This strategy might improve the efficacy of the vaccines used in the partially successful RV144 HIV vaccine trial, where the two CRF01_AE immunogens (derived from the A244 and TH023 isolates) both possessed glycosylation sites at N136 and N149.