Pascal Cosette

Isolation, characterization, and distribution of a novel neuropeptide, Rana RFamide (R-RFa), in the Brain of the european green frog Rana esculenta

A novel neuropeptide of the RFamide peptide family was isolated in pure form from a frog (Rana esculenta) brain extract by using reversed‐phase high performance liquid chromatography in combination with a radioimmunoassay for mammalian neuropeptide FF (NPFF). The primary structure of the peptide was established as Ser‐Leu‐Lys‐ Pro‐Ala‐Ala‐Asn‐Leu‐Pro‐Leu‐ Arg‐Phe‐NH2. The sequence of this neuropeptide, designated Rana RFamide (R‐RFa), exhibits substantial similarities with those of avian LPLRFamide, gonadotropin‐inhibitory hormone, and human RFRP‐1. The distribution of R‐RFa was investigated in the frog central nervous system by using an antiserum directed against bovine NPFF. In the brain, immunoreactive cell bodies were primarily located in the hypothalamus, i.e., the anterior preoptic area, the suprachiasmatic nucleus, and the dorsal and ventral hypothalamic nuclei. The most abundant population of R‐RFa–containing neurons was found in the periependymal region of the suprachiasmatic nucleus. R‐RFa– containing fibers were widely distributed throughout the brain from the olfactory bulb to the brainstem, and were particularly abundant in the external layer of the median eminence. In the spinal cord, scattered immunoreactive neurons were found in the gray matter. R‐RFa–positive processes were found in all regions of the spinal cord, but they were more abundant in the dorsal horn. This study provides the first characterization of a member of the RFamide peptide family in amphibians. The occurrence of this novel neuropeptide in the hypothalamus and median eminence and in the dorsal region of the spinal cord suggests that, in frog, R‐RFa may exert neuroendocrine activities and/or may be involved in the transmission of nociceptive stimuli. J. Comp. Neurol. 448:111–127, 2002.

Adhesion of Yersinia ruckeri to fish farm materials: influence of cell and material surface properties

Abstract Two strains (an environmental strain and a reference one coming from a national culture collection) of Yersinia ruckeri , a fish pathogenic bacterium, are characterised according to the ability to adhere on wood, concrete, polyvinylchloride (PVC) and fibreglass, four materials commonly found in fish farms. The relationships between adherence, bacterial and support hydrophobicities and surface roughness are investigated. The results show that: (i) Y. ruckeri is strongly hydrophilic; (ii) the environmental strain exhibits a higher ability to adhere than the reference one; and (iii) for the two strains a strong correlation is observed between roughness amplitude (RA) of the support material and adhesion ability.

Growth Retardation, Reduced Invasiveness, and Impaired Colistin-Mediated Cell Death Associated with Colistin Resistance Development in Acinetobacter baumannii

ABSTRACT Two colistin-susceptible/colistin-resistant (Cols/Colr) pairs of Acinetobacter baumannii strains assigned to international clone 2, which is prevalent worldwide, were sequentially recovered from two patients after prolonged colistin administration. Compared with the respective Cols isolates (Ab248 and Ab299, both having a colistin MIC of 0.5 μg/ml), both Colr isolates (Ab249 and Ab347, with colistin MICs of 128 and 32 μg/ml, respectively) significantly overexpressed pmrCAB genes, had single-amino-acid shifts in the PmrB protein, and exhibited significantly slower growth. The Colr isolate Ab347, tested by proteomic analysis in comparison with its Cols counterpart Ab299, underexpressed the proteins CsuA/B and C from the csu operon (which is necessary for biofilm formation). This isolate also underexpressed aconitase B and different enzymes involved in the oxidative stress response (KatE catalase, superoxide dismutase, and alkyl hydroperoxide reductase), suggesting a reduced response to reactive oxygen species (ROS) and, consequently, impaired colistin-mediated cell death through hydroxyl radical production. Cols isolates that were indistinguishable by macrorestriction analysis from Ab299 caused six sequential bloodstream infections, and isolates indistinguishable from Ab248 caused severe soft tissue infection, while Colr isolates indistinguishable from Ab347 and Ab249 were mainly colonizers. In particular, a Cols isolate identical to Ab299 was still invading the bloodstream 90 days after the colonization of this patient by Colr isolates. These observations indicate considerably lower invasiveness of A. baumannii clinical isolates following the development of colistin resistance.

VBNC Legionella pneumophila cells are still able to produce virulence proteins

Legionella pneumophila is the agent responsible for legionellosis. Numerous bacteria, including L. pneumophila, can enter into a viable but not culturable (VBNC) state under unfavorable environmental conditions. In this state, cells are unable to form colonies on standard medium but are still alive. Here we show that VBNC L. pneumophila cells, obtained by monochloramine treatment, were still able to synthesize proteins, some of which are involved in virulence. Protein synthesis was measured using (35)S-labeling and the proteomes of VBNC and culturable cells then compared. This analysis allowed the identification of nine proteins that were accumulated in the VBNC state. Among them, four were involved in virulence, i.e., the macrophage infectivity potentiator protein, the hypothetical protein lpl2247, the ClpP protease proteolytic subunit and the 27 kDa outer membrane protein. Others, i.e., the enoyl reductase, the electron transfer flavoprotein (alpha and beta subunits), the 50S ribosomal proteins (L1 and L25) are involved in metabolic and energy production pathways. However, resuscitation experiments performed with Acanthamoeba castellanii failed, suggesting that the accumulation of virulence factors by VBNC cells is not sufficient to maintain their virulence.

Impact of rpoS deletion on the proteome of Escherichia coli grown planktonically and as biofilm.

To investigate the role of rpoS in gene expression of Escherichia coli cells grown as biofilms, we compared the proteomes of a rpoS mutant and the wild-type strain. Experiments were performed on planktonic cells (in exponential or stationary growth phase) and biofilms developed on glass wool. Spot-by-spot comparison of gels obtained from biofilm and planktonic wild-type organisms showed that the intensity of between 22 and 30% of detected spots was affected by the growth mode, depending of the control used. Principal component analysis, used to interpret the variations in protein spot densities, discriminated exponential-phase cells (wild-type and mutant) from the other incubation conditions and secondarily 72-old cultures. The statistical analysis demonstrated that the rpoS mutation did not significantly modify the proteome of exponential-growth phase cells, the differences involving only 3% of the proteome. However, increasing the incubation time from 8 to 72 h noticeably increased the number of changed proteins. A cluster analysis showed that RpoS plays a role in the special nature of the gene expression of biofilm cells but lower than in stationary-phase bacteria. We identified 35 rpoS-regulated proteins that were already or not described as controlled by this sigma factor. For some of them, the mode of regulation by RpoS was obviously dependent on the culture condition (planktonic vs biofilm).

Structure and functions of the novel hypothalamic RFamide neuropeptides R-RFa and 26RFa in vertebrates.

A number of RFamide peptides have been characterized in invertebrate species and these peptides have been found to exert a broad spectrum of biological activities. In contrast, in vertebrates, our knowledge on RFamide peptides is far more limited and only a few members of the RFamide peptide family have been identified in various vertebrate classes during the last years. The present review focuses on two novel RFamide peptides, Rana RFamide (R-RFa) and 26RFa, that have been recently isolated from the amphibian brain. R-RFa shares the C-terminal LPLRFamide motif with other RFamide peptides previously identified in mammals, birds and fish. The distribution of R-RFa in the frog brain exhibits strong similarities with those of other LPLRFamide peptides, notably in the periventricular region of the hypothalamus. There is also evidence that the physiological functions of R-RFa and other LPLRFamide peptides have been conserved from fish to mammals; in particular, all these peptides appear to be involved in the control of pituitary hormone secretion. 26RFa does not exhibit any significant structural identity with other RFamide peptides and this peptide is the only member of the family that possesses an FRFamide motif at its C-terminus. The strong conservation of the primary structure of 26RFa from amphibians to mammals suggests that this RFamide peptide is involved in important biological functions in vertebrates. As for several other RFamide peptides, 26RFa-containing neurons are present in the hypothalamus, notably in two nuclei involved in the control of feeding behavior. Indeed, 26RFa is a potent stimulator of appetite in mammals. Concurrently, recent data suggest that 26RFa exerts various neuroendocrine regulatory activities at the pituitary and adrenal level.

Anti-candida effect of bacillomycin D-like lipopeptides from Bacillus subtilis B38.

Bacillus subtilis B38, isolated from soil, showed antimicrobial activity against human pathogenic Candida albicans species. Specific PCR primers revealed the presence of the bamC gene, which is involved in the biosynthesis of bacillomycin D. Three anti-Candida compounds designated a(1) , a(2) and a(3) were purified from culture supernatant and identified using matrix-assisted laser desorption/ionization time-of-flight MS as analogues of bacillomycin D-like lipopeptides of 14, 15 and 16 carbon fatty acid long chains, respectively. The compound a(3) displayed the strongest fungicidal activity against pathogenic C. albicans strains. It was even more active than amphotericin B with a lethal concentration of 59.07 vs. 135.26 μM of the antimycotic drug against the pathogenic strain C. albicans sp. 311 isolated from finger nail. Only moderate or weak anti-Candida activity was recorded for a(1) and a(2) compounds. Furthermore, a(3) showed the highest hemolytic activity, reaching 50% hemolysis at 22.14 μM, whereas a(1) and a(2) displayed a limited hemolysis at 68.26 and 37.41 μM, respectively. These findings suggest that the acyl chain length of bacillomycin D-like lipopeptides plays a major role in hemolytic and antifungal activities.

Purification and characterization of antimicrobial peptides from the skin secretions of the carpenter frog Rana virgatipes (Ranidae, Aquarana).

The members of the Aquarana (or Rana catesbeiana species group) form a well-supported monophyletic clade but phylogenetic relationships between species within the group are incompletely understood. Peptides that differentially inhibited the growth of bacteria were purified from electrically stimulated skin secretions of the carpenter frog Rana virgatipes. Structural characterization identified members of the ranatuerin-2 (3 peptides) and temporin (3-peptides) families, previously found in the skins of R. catesbeiana, R. clamitans, R. grylio and R. septentrionalis. Ranalexin, a peptide previously found only in the Aquarana, was isolated together with a variant (FFGLHNLVPSMLCVVRKKC) that lacks the propensity to adopt an alpha-helical conformation and so was devoid of antimicrobial activity. Two C-terminally alpha-amidated peptides belonging to the brevinin-2 family were isolated from the skin secretions that, like an ortholog from R. septentrionalis, lacked the C-terminal cyclic heptapeptide domain associated with members of this family. Ranatuerin-1, previously isolated from R. catesbeiana, R. clamitans and R. grylio but absent from R. septentrionalis, was also not identified in R. virgatipes. Synthetic replicates of temporin-1Va (FLSSIGKILGNLL.NH2), temporin-IVb (FLSIIAKVLGSLF.NH2) and temporin-1Vc (FLPLVTMLLGKLF.NH2) potently inhibited growth of Gram-positive bacteria (including methicillin-resistant Staphylococcus aureus). Temporin-1Va was also active against Gram-negative bacteria and the opportunistic yeast pathogen Candida albicans and had relatively weak hemolytic activity (LD50=120 microM) and may therefore represent a candidate for drug development. Our data support the placement of R. virgatipes in the Aquarana and indicate a closer phylogenetic relationship of R. virgatipes with R. septentrionalis than with R. catesbeiana, R. clamitans and R. grylio.

Antimicrobial peptides from diverse families isolated from the skin of the Asian frog, Rana grahami.

Seven peptides with antimicrobial activity were isolated in pure form from an extract of the skin of the Yunnanfu Kunming frog Rana grahami Boulenger, 1917. The peptides were identified as belonging to the nigrocin-2 (three peptides), brevinin-1 (one peptide), brevinin-2 (three peptides), and esculentin-1 (one peptide) families. Nigrocin-2GRb (GLFGKILGVGKKVLCGLSGMC) containing three lysine residues, represented the peptide with highest potency against microorganisms (MIC = 3 microM against Escherichia coli, 12.5 microM against Staphylococcus aureus and 50 microM against Candida albicans) and the greatest hemolytic activity against human erythrocytes (LD50 = 40 microM). In contrast, nigrocin-2GRa (GLLSGILGAGKHIVCGLSGLC) and nigrocin-2GRc (GLLSGILGAGKNIVCGLSGLC), with only a single lysine residue, showed weak antimicrobial and hemolytic activity. Phylogenetic relationships among Eurasian ranid frogs are less well understood than those of North American ranids but the primary structures of the R. grahami antimicrobial peptides suggest a close relationship of this species with the Japanese pond frogs R. nigromaculata and R. porosa brevipoda.

Identification of Biofilm-Associated Cluster (bac) in Pseudomonas aeruginosa Involved in Biofilm Formation and Virulence

Biofilms are prevalent in diseases caused by Pseudomonas aeruginosa, an opportunistic and nosocomial pathogen. By a proteomic approach, we previously identified a hypothetical protein of P. aeruginosa (coded by the gene pA3731) that was accumulated by biofilm cells. We report here that a ΔpA3731 mutant is highly biofilm-defective as compared with the wild-type strain. Using a mouse model of lung infection, we show that the mutation also induces a defect in bacterial growth during the acute phase of infection and an attenuation of the virulence. The pA3731 gene is found to control positively the ability to swarm and to produce extracellular rhamnolipids, and belongs to a cluster of 4 genes (pA3729–pA3732) not previously described in P. aeruginosa. Though the protein PA3731 has a predicted secondary structure similar to that of the Phage Shock Protein, some obvious differences are observed compared to already described psp systems, e.g., this unknown cluster is monocistronic and no homology is found between the other proteins constituting this locus and psp proteins. As E. coli PspA, the amount of the protein PA3731 is enlarged by an osmotic shock, however, not affected by a heat shock. We consequently named this locus bac for biofilm-associated cluster.