Byssochlamys nivea as a Source of Mycophenolic Acid

Byssochlamys species are responsible for spoilage and degradation of fruits and silages and can also produce the mycotoxin patulin. We analyzed secondary metabolite production by Byssochlamys nivea. Mycophenolic acid and its precursors, 5-methylorsellinic acid and 5,7-dihydroxy-4-methylphthalide, were identified in all of the B. nivea strains that we examined.     

Synthesis and conformational studies of pseudopeptides containing an unsymmetrical triazine scaffold.

Solid-phase synthesis and conformational studies of two pseudopeptides constituted by a triazine scaffold bound to two peptidic arms are described. In this paper, a new scaffold based on unsymmetrical triamino 1,3,5-triazine bearing two alkyl chains has been designed, assisted by molecular modelling, as a mimic of the backbone of the i + 1 and i + 2 residues of a beta-turn. The results confirm the ability of the triazine scaffold to induce extended conformations of the peptidic strands and point out that this scaffold is a good candidate as a template to induce anti-parallel beta-sheet structure.     

Identification and characterization of the receptor for the Bacillus sphaericus binary toxin in the malaria vector mosquito, Anopheles gambiae

The binary toxin (Bin) from Bacillus sphaericus exhibits a highly insecticidal activity against Culex and Anopheles mosquitoes. The cytotoxicity of Bin requires an interaction with a specific receptor present on the membrane of midgut epithelial cells in larvae. A direct correlation exists between binding affinity and toxicity. The toxin binds with high affinity to its receptor in its primary target, Culex pipiens, and displays a lower affinity to the receptor in Anopheles gambiae, which is less sensitive to Bin. Although the Bin receptor has previously been identified and named Cpm1 in C. pipiens, its structure in Anopheles remains unknown. In this study, we hypothesize that the Anopheles Bin receptor is an ortholog of Cpm1. By screening the Anopheles genomic database, we identified a candidate gene (Agm3) which is expressed primarily on the surface of midgut cells in larvae and which functions as a receptor for Bin. A Cpm1-like gene is also present in the Bin-refractory species Aedes aegypti. Overall, our results indicate that the three mosquito genes examined share a very similar organization and are strongly conserved at the amino acid level, in particular in the NH(2)-terminus, a region believed to contain the ligand binding site, suggesting that relatively few amino acids residues are critical for high affinity binding of the toxin.     

Acute infection by conjunctival route with Brucella melitensis induces IgG+ cells and IFN-gamma producing cells in peripheral and mucosal lymph nodes in sheep

The early distribution of Brucella melitensis and the immune response induced in lymphoid tissues and lymph nodes (LN) draining the upper respiratory tract were analysed in sheep. An experimental acute infection was performed by inoculating the sheep with the virulent H38 strain of B. melitensis by the conjunctival route. The infection was rapidly controlled at the site of inoculation but resulted in a local and systemic dissemination of brucellae mainly in the pharyngeal tonsil, local and peripheral LN and the spleen. The control of the infection was associated with the induction of a specific immune response characterized by an increase in IgG+ cells, the production of IFN-gamma and IL-10 by cells from draining parotid, retropharyngeal and submaxillary LN, but also from more distant peripheral prescapular and mesenteric LN. IFN-gamma was produced by CD4+, CD8+ and CD4(-)CD8(-)gammadelta(-) cells and probably contributed to the control of both local and systemic infection.     

Two molecular features contribute to the Argonaute specificity for the microRNA and RNAi pathways in C. elegans

In Caenorhabditis elegans, specific Argonaute proteins are dedicated to the RNAi and microRNA pathways. To uncover how the precise Argonaute selection occurs, we designed dsRNA triggers containing both miRNA and siRNA sequences. While dsRNA carrying nucleotides mismatches can only enter the miRNA pathway, a fully complementary dsRNA successfully rescues let-7 miRNA function and initiates silencing by RNAi. We demonstrated that RDE-1 is essential for RNAi induced by the perfectly paired trigger, yet is not required for silencing by the let-7 miRNA. In contrast, ALG-1/ALG-2 are required for the miRNA function, but not for the siRNA-directed gene silencing. Finally, a dsRNA containing a bulged miRNA and a perfectly paired siRNA can enter both pathways suggesting that the sorting of small RNAs occurs after that the dsRNA trigger has been processed by Dicer. Thus, our data suggest that the selection of Argonaute proteins is affected by two molecular features: (1) the structure of the small RNA duplex; and (2) the Argonautes specific characteristics.     

Effect of 2,4,6-trinitrotoluene on soil bacterial communities

To gain insight into the impact of 2,4,6-trinitrotoluene (TNT) on soil microbial communities, we characterized the bacterial community of several TNT-contaminated soils from two sites with different histories of contamination and concentrations of TNT. The amount of extracted DNA, the total cell counts and the number of CFU were lower in the TNT-contaminated soils. Analysis of soil bacterial diversity by DGGE showed a predominance of Pseudomonadaceae and Xanthomonadaceae in the TNT-contaminated soils, as well as the presence of Caulobacteraceae. CFU from TNT-contaminated soils were identified as Pseudomonadaceae, and, to a lesser extent, Caulobacteraceae. Finally, a pristine soil was spiked with different concentrations of TNT and the soil microcosms were incubated for 4 months. The amount of extracted DNA decreased in the microcosms with a high TNT concentration [1.4 and 28.5 g TNT/kg (dry wt) of soil] over the incubation period. After 7 days of incubation of these soil microcosms, there was already a clear shift of their original flora towards a community dominated by Pseudomonadaceae, Xanthomonadaceae, Comamonadaceae and Caulobacteraceae. These results indicate that TNT affects soil bacterial diversity by selecting a narrow range of bacterial species that belong mostly to Pseudomonadaceae and Xanthomonadaceae.     

Diel rhythmicity in amino acid uptake by Prochlorococcus

The marine cyanobacterium Prochlorococcus , the most abundant phototrophic organism on Earth, numerically dominates the phytoplankton in nitrogen (N)-depleted oceanic gyres. Alongside inorganic N sources such as nitrite and ammonium, natural populations of this genus also acquire organic N, specifically amino acids. Here, we investigated using isotopic tracer and flow cytometric cell sorting techniques whether amino acid uptake by Prochlorococcus is subject to a diel rhythmicity, and if so, whether this was linked to a specific cell cycle stage. We observed, in contrast to diurnally similar methionine uptake rates by Synechococcus cells, obvious diurnal rhythms in methionine uptake by Prochlorococcus cells in the tropical Atlantic. These rhythms were confirmed using reproducible cyclostat experiments with a light-synchronized axenic Prochlorococcus (PCC9511 strain) culture and ³⁵S-methionine and ³H-leucine tracers. Cells acquired the tracers at lower rates around dawn and higher rates around dusk despite >10⁴ times higher concentration of ammonium in the medium, presumably because amino acids can be directly incorporated into protein. Leucine uptake rates by cells in the S+G₂ cell cycle stage were consistently 2.2 times higher than those of cells at the G₁ stage. Furthermore, S+G₂ cells upregulated amino acid uptake 3.5 times from dawn to dusk to boost protein synthesis prior to cell division. Because Prochlorococcus populations can account from 13% at midday to 42% at dusk of total microbial uptake of methionine and probably of other amino acids in N-depleted oceanic waters, this genus exerts diurnally variable, strong competitive pressure on other bacterioplankton populations.     

Spindle-localized CPE-mediated translation controls meiotic chromosome segregation

Meiotic progression requires the translational activation of stored maternal mRNAs, such as those encoding cyclin B1 or mos. The translation of these mRNAs is regulated by the cytoplasmic polyadenylation element (CPE) present in their 3'UTRs, which recruits the CPE-binding protein CPEB. This RNA-binding protein not only dictates the timing and extent of translational activation by cytoplasmic polyadenylation but also participates, together with the translational repressor Maskin, in the transport and localization, in a quiescent state, of its targets to subcellular locations where their translation will take place. During the early development of Xenopus laevis, CPEB localizes at the animal pole of oocytes and later on at embryonic spindles and centrosomes. Disruption of embryonic CPEB-mediated translational regulation results in abnormalities in the mitotic apparatus and inhibits embryonic mitosis. Here we show that spindle-localized translational activation of CPE-regulated mRNAs, encoding for proteins with a known function in spindle assembly and chromosome segregation, is essential for completion of the first meiotic division and for chromosome segregation in Xenopus oocytes.