(1/930) Inhibition of vibrio anguillarum by Pseudomonas fluorescens AH2, a possible probiotic treatment of fish.
To study the possible use of probiotics in fish farming, we evaluated the in vitro and in vivo antagonism of antibacterial strain Pseudomonas fluorescens strain AH2 against the fish-pathogenic bacterium Vibrio anguillarum. As iron is important in virulence and bacterial interactions, the effect of P. fluorescens AH2 was studied under iron-rich and iron-limited conditions. Sterile-filtered culture supernatants from iron-limited P. fluorescens AH2 inhibited the growth of V. anguillarum, whereas sterile-filtered supernatants from iron-replete cultures of P. fluorescens AH2 did not. P. fluorescens AH2 inhibited the growth of V. anguillarum during coculture, independently of the iron concentration, when the initial count of the antagonist was 100 to 1, 000 times greater that of the fish pathogen. These in vitro results were successfully repeated in vivo. A probiotic effect in vivo was tested by exposing rainbow trout (Oncorynchus mykiss Walbaum) to P. fluorescens AH2 at a density of 10(5) CFU/ml for 5 days before a challenge with V. anguillarum at 10(4) to 10(5) CFU/ml for 1 h. Some fish were also exposed to P. fluorescens AH2 at 10(7) CFU/ml during the 1-h infection. The combined probiotic treatment resulted in a 46% reduction of calculated accumulated mortality; accumulated mortality was 25% after 7 days at 12 degrees C in the probiotic-treated fish, whereas mortality was 47% in fish not treated with the probiont. (+info)
(2/930) IC202A, a new siderophore with immunosuppressive activity produced by Streptoalloteichus sp. 1454-19. I. Taxonomy, fermentation, isolation and biological activity.
IC202A, a new immunosuppressive compound, was isolated from the culture filtrate of Streptoalloteichus sp. 1454-19. It showed a suppressive effect on mixed lymphocyte culture reaction with an IC50 value of 3.6 microg/ml and mitogen induced lymphocyte blastogenesis in vitro. (+info)
(3/930) IC202A, a new siderophore with immunosuppressive activity produced by Streptoalloteichus sp. 1454-19. II. Physico-chemical properties and structure elucidation.
IC202A (1) was isolated from the culture filtrate of Streptoalloteichus sp. 1454-19. The structure of 1 was determined by spectral analysis including a variety of two-dimentional NMR and FAB-MS experiments. IC202A is a ferrioxamine-related compound containing a butylidene N-oxide function. (+info)
(4/930) Ferrioxamine-mediated Iron(III) utilization by Salmonella enterica.
Utilization of ferrioxamines as sole sources of iron distinguishes Salmonella enterica serotypes Typhimurium and Enteritidis from a number of related species, including Escherichia coli. Ferrioxamine supplements have therefore been used in preenrichment and selection media to increase the bacterial growth rate while selectivity is maintained. We characterized the determinants involved in utilization of ferrioxamines B, E, and G by S. enterica serotype Typhimurium by performing siderophore cross-feeding bioassays. Transport of all three ferric siderophores across the outer membrane was dependent on the FoxA receptor encoded by the Fur-repressible foxA gene. However, only the transport of ferrioxamine G was dependent on the energy-transducing protein TonB, since growth stimulation of a tonB strain by ferrioxamines B and E was observed, albeit at lower efficiencies than in the parental strain. Transport across the inner membrane was dependent on the periplasmic binding protein-dependent ABC transporter complex comprising FhuBCD, as has been reported for other hydroxamate siderophores of enteric bacteria. The distribution of the foxA gene in the genus Salmonella, as indicated by DNA hybridization studies and correlated with the ability to utilize ferrioxamine E, was restricted to subspecies I, II, and IIIb, and this gene was absent from subspecies IIIa, IV, VI, and VII (formerly subspecies IV) and Salmonella bongori (formerly subspecies V). S. enterica serotype Typhimurium mutants with either a transposon insertion or a defined nonpolar frameshift (+2) mutation in the foxA gene were not able to utilize any of the three ferrioxamines tested. A strain carrying the nonpolar foxA mutation exhibited a significantly reduced ability to colonize rabbit ileal loops compared to the foxA+ parent. In addition, a foxA mutant was markedly attenuated in mice inoculated by either the intragastric or intravenous route. Mice inoculated with the foxA mutant were protected against subsequent challenge by the foxA+ parent strain. (+info)
(5/930) The fhu genes of Rhizobium leguminosarum, specifying siderophore uptake proteins: fhuDCB are adjacent to a pseudogene version of fhuA.
A mutant of Rhizobium leguminosarum was isolated which fails to take up the siderophore vicibactin. The mutation is in a homologue of fhuB, which in Escherichia coli specifies an inner-membrane protein of the ferric hydroxamate uptake system. In Rhizobium, fhuB is in an operon fhuDCB, which specifies the cytoplasmic membrane and periplasmic proteins involved in siderophore uptake. fhuDCB mutants make vicibactin when grown in Fe concentrations that inhibit its production in the wild-type. Nodules on peas induced by fhuDCB mutants were apparently normal in N2 fixation. Transcription of an fhuDCB-lacZ fusion was Fe-regulated, being approximately 10-fold higher in Fe-depleted cells. Downstream of fhuB, in the opposite orientation, is a version of fhuA whose homologues in other bacteria specify hydroxamate outer-membrane receptors. This fhuA gene appears to be a pseudogene with stop codons and undetectable expression. (+info)
(6/930) Multiple haem-utilization loci in Helicobacter pylori.
To identify genes responsible for the utilization of haem as an iron source in Helicobacter pylori, a siderophore synthesis mutant of Escherichia coli was transformed with an ordered cosmid library of H. pylori NCTC 11638. Four independent cosmids were found that were able to complement this mutant on iron-restrictive solid media containing different haem compounds as the sole source of iron. Hybridization experiments revealed that the four cosmids contained unrelated DNA fragments. No major differences were observed in the growth of the four transformants on iron-restrictive solid media to which different haem compounds had been added. None of the cosmids could confer the ability to use haem as an iron source to an E. coli aroB tonB mutant, which means that transport of iron and/or haem across the outer membrane requires a functional TonB protein. Further characterization of the cosmids revealed that one of them was also able to complement E. coli aroB hemA, indicating that the haem molecule is taken up as a whole by this haem-biosynthesis mutant. Expression of this haem-uptake system could not be repressed by excess iron. Another cosmid expressed two polypeptides in E. coli which were specifically immunoreactive with a polyclonal antiserum raised against whole cells of H. pylori. The production of these proteins appeared to be iron repressible. One of these proteins has the same molecular mass as a previously described 77 kDa haem-binding iron-repressible outer-membrane protein (IROMP) of H. pylori. (+info)
(7/930) The siderophore 2,3-dihydroxybenzoic acid is not required for virulence of Brucella abortus in BALB/c mice.
2,3-Dihydroxybenzoic acid (DHBA) is the only siderophore described for Brucella, and previous studies suggested that DHBA might contribute to the capacity of these organisms to persist in host macrophages. Employing an isogenic siderophore mutant (DeltaentC) constructed from virulent Brucella abortus 2308, however, we found that production of DHBA is not required for replication in cultured murine macrophages or for the establishment and maintenance of chronic infection in the BALB/c mouse model. (+info)
(8/930) Environmental factors modulating antibiotic and siderophore biosynthesis by Pseudomonas fluorescens biocontrol strains.
Understanding the environmental factors that regulate the biosynthesis of antimicrobial compounds by disease-suppressive strains of Pseudomonas fluorescens is an essential step toward improving the level and reliability of their biocontrol activity. We used liquid culture assays to identify several minerals and carbon sources which had a differential influence on the production of the antibiotics 2,4-diacetylphloroglucinol (PHL), pyoluteorin (PLT), and pyrrolnitrin and the siderophores salicylic acid and pyochelin by the model strain CHA0, which was isolated from a natural disease-suppressive soil in Switzerland. Production of PHL was stimulated by Zn2+, NH4Mo2+, and glucose; the precursor compound mono-acetylphloroglucinol was stimulated by the same factors as PHL. Production of PLT was stimulated by Zn2+, Co2+, and glycerol but was repressed by glucose. Pyrrolnitrin production was increased by fructose, mannitol, and a mixture of Zn2+ and NH4Mo2+. Pyochelin production was increased by Co2+, fructose, mannitol, and glucose. Interestingly, production of its precursor salicylic acid was increased by different factors, i.e., NH4Mo2+, glycerol, and glucose. The mixture of Zn2+ and NH4Mo2+ with fructose, mannitol, or glycerol further enhanced the production of PHL and PLT compared with either the minerals or the carbon sources used alone, but it did not improve siderophore production. Extending fermentation time from 2 to 5 days increased the accumulation of PLT, pyrrolnitrin, and pyochelin but not of PHL. When findings with CHA0 were extended to an ecologically and genetically diverse collection of 41 P. fluorescens biocontrol strains, the effect of certain factors was strain dependent, while others had a general effect. Stimulation of PHL by Zn2+ and glucose was strain dependent, whereas PLT production by all strains that can produce this compound was stimulated by Zn2+ and transiently repressed by glucose. Inorganic phosphate reduced PHL production by CHA0 and seven other strains tested but to various degrees. Production of PLT but not pyrrolnitrin by CHA0 was also reduced by 100 mM phosphate. The use of 1/10-strength nutrient broth-yeast extract, compared with standard nutrient broth-yeast extract, amended with glucose and/or glycerol resulted in dramatically increased accumulations of PHL (but not PLT), pyochelin, and salicylic acid, indicating that the ratio of carbon source to nutrient concentration played a key role in the metabolic flow. The results of this study (i) provide insight into the biosynthetic regulation of antimicrobial compounds, (ii) limit the number of factors for intensive study in situ, and (iii) indicate factors that can be manipulated to improve bacterial inoculants. (+info)