The Experts below are selected from a list of 3705 Experts worldwide ranked by ideXlab platform

Lynne Dobson - One of the best experts on this subject based on the ideXlab platform.

  • A quantitative study of the relationships between morphology, physiology and geldanamycin synthesis in submerged cultures of Streptomyces hygroscopicus var. geldanus
    2008
    Co-Authors: Lynne Dobson
    Abstract:

    Microbially produced secondary metabolites such as antibiotics have tremendous economic importance. However, most are produced by filamentous organisms which exhibit diverse growth patterns presenting challenges for industrial fermentation. There are many factors affecting secondary metabolite production which concomitantly impact on morphology, thus it is difficult to distinguish the key driver for productivity. Streptomyces spp. is a genus of filamentous organisms that together synthesise over 4000 bioactive compounds. Streptomyces hygroscopicus var. geldanus produces the secondary metabolite geldanamycin, a novel chemotherapeutic compound, in submerged fermentation. This organism represents an ideal system for experimentation in order to elucidate the relationships between morphology, physiology and secondary metabolite production. The effects of a variety of microbiological (inoculum size), physical (glass beads) and chemical (surfactants, calcium ions, magnesium ions) factors on morphological development were examined as part of this study. Inclusion of the divalent cations magnesium or calcium was demonstrated to alter the cell surface hydrophobicity of the organism, provoking dispersion or aggregation of cells respectively, and stimulating great disparity in geldanamycin yields. Indeed, in all instances, morphology was found to impact considerably on secondary metabolite formation, with smaller pellet sizes optimal for geldanamycin synthesis. Investigation of the respiration rate of Streptomyces hygroscopicus var. geldanus revealed that a linear relationship existed between this parameter and geldanamycin production. Submerged cultures consisting primarily of small pellets, less than 0.5mm in diameter, were more metabolically active and concomitantly produced more geldanamycin. Nonetheless, it was also demonstrated that other explicit factors exist which do not affect morphology or respiration but regulate geldanamycin synthesis through feedback inhibition of the direct metabolic pathway. This study has demonstrated that, in Streptomyces hygroscopicus var. geldanus, the bulk of factors that affect morphology impact significantly on respiration, and it is this parameter that is the key driver of secondary metabolite production. This case study provides new insights into the regulation of geldanamycin production in Streptomyces hygroscopicus var. geldanus and provides a basis for elucidation of the relationships between morphology, physiology and secondary metabolism in other filamentous micro-organisms.

  • The influence of morphology on geldanamycin production in submerged fermentations of Streptomyces hygroscopicus var. geldanus.
    Applied microbiology and biotechnology, 2008
    Co-Authors: Lynne Dobson, Cormac C. O’cleirigh, Daniel G O'shea
    Abstract:

    The diverse morphology of the filamentous organism Streptomyces hygroscopicus var. geldanus was characterised by image analysis under various environmental conditions. In the presence of surfactant compounds, a significant decrease in the mean pellet diameter was observed. Cell aggregation was also influenced by spore inoculum level, with high concentrations reducing pellet size. In addition, the dispersion of pellets was found to increase with the inclusion of glass beads to submerged shake-flask cultures. In all cases, production of the secondary metabolite geldanamycin was determined to be dependent on the morphological profile of the organism, with a concomitant increase of 88% in geldanamycin yield observed as the mean pellet diameter was reduced by 70%. Thus, to maximise the yield of geldanamycin, it is necessary to limit pellet formation in Streptomyces hygroscopicus var. geldanus to an appropriate size.

Daniel G O'shea - One of the best experts on this subject based on the ideXlab platform.

  • The influence of morphology on geldanamycin production in submerged fermentations of Streptomyces hygroscopicus var. geldanus.
    Applied microbiology and biotechnology, 2008
    Co-Authors: Lynne Dobson, Cormac C. O’cleirigh, Daniel G O'shea
    Abstract:

    The diverse morphology of the filamentous organism Streptomyces hygroscopicus var. geldanus was characterised by image analysis under various environmental conditions. In the presence of surfactant compounds, a significant decrease in the mean pellet diameter was observed. Cell aggregation was also influenced by spore inoculum level, with high concentrations reducing pellet size. In addition, the dispersion of pellets was found to increase with the inclusion of glass beads to submerged shake-flask cultures. In all cases, production of the secondary metabolite geldanamycin was determined to be dependent on the morphological profile of the organism, with a concomitant increase of 88% in geldanamycin yield observed as the mean pellet diameter was reduced by 70%. Thus, to maximise the yield of geldanamycin, it is necessary to limit pellet formation in Streptomyces hygroscopicus var. geldanus to an appropriate size.

Ivanova - One of the best experts on this subject based on the ideXlab platform.

  • Calcium ions and the differentiation of Streptomyces hygroscopicus 155, a producer of an antibiotic complex
    Antibiotiki i khimioterapiia = Antibiotics and chemoterapy [sic], 2000
    Co-Authors: Ivanova
    Abstract:

    The effect of Ca2+ on differentiation of Streptomyces hygroscopicus 155 and its inactive variant 155-0 was studied. Addition of Ca2+ to the medium induced formation of the aerial mycelium in the inactive variant and accelerated formation of the aerial mycelium in the parent strain. The inhibitory effect of EGTA, verapamil, nifedipin, chlorpromazine and dilthiazeme on the aerial mycelium formation demonstrated the physiological role of Ca2+ in the process. Addition of pandavir (nigericin) and azalomycin B, the antibiotics produced by the streptomycete, induced formation of the aerial mycelium in the inactive variant. The effect was higher in the presence of Ca2+. Streptomyces hygroscopicus 155 and its inactive variant synthesized a proteolytic complex containing metalloproteases and trypsin-like proteases. The total proteolytic activity of the inactive variant was lower than that of the parent strain. Addition of Ca2+ to the medium stimulated their proteolytic activity. The inducing action of the antibiotics produced by the parent strain on differentiation of S.hygroscopicus 155-0 and the increase of their action in the presence of Ca2+ suggested that they controlled the differentiation and that such a function of the antibiotics expressed itself through the Ca2+ signal system.

  • Glutamate oxalacetate and glutamate pyruvate aminotransferase activity in Streptomyces hygroscopicus 155 producing antibiotic complex
    Antibiotiki i khimioterapiia = Antibiotics and chemoterapy [sic], 1997
    Co-Authors: Ivanova, Gocheva B
    Abstract:

    Antibiotic activity, aminotransferase activity and composition of intracellular amino acids in low and high potent variants of Streptomyces hygroscopicus 155 were studied. The data of the study are indicative of some general regularities characteristic of amino acid metabolism in actinomycetes: an increased pool of the main aminodonor amino acids (alanine, asparaginic and glutaminic acids) and an increased activity of aminotransferases in the cultures of both the variants when grown in media with readily assimilable nitrogen sources.

  • Resistance of the strain Streptomyces hygroscopicus 155 to autogenous and other antibiotics
    Antibiotiki i khimioterapiia = Antibiotics and chemoterapy [sic], 1992
    Co-Authors: Ivanova
    Abstract:

    Streptomyces hygroscopicus 155, a strain producing pandavir (nigericin) and azalomycin, was studied with respect to resistance to its own and some other antibiotics i.e. tetracycline, gentamicin, streptomycin, erythromycin, tylosin, thiostreptone, benzylpenicillin, monensin and salinomycin. An inactive variant of the culture was used in the control.

  • Preparation and regeneration of protoplasts of the strain Streptomyces hygroscopicus 155
    Antibiotiki i khimioterapiia = Antibiotics and chemoterapy [sic], 1992
    Co-Authors: Ivanova
    Abstract:

    Protoplasts of Streptomyces hygroscopicus 155 producing nigericin, a polyether antibiotic, were prepared. Conditions for protoplasting and optimal concentrations of lysozyme and glycine, and the age of mycelium were studied. With the method of the experiment design, concentrations of four components: CaCl2, MgCl2, KH2PO4 and TES buffer in the regeneration medium were determined. The levels of CaCl2 and TES buffer proved to be the most important parameters.

  • Effect of protoplasting on antibiotic activity and resistance in the strain Streptomyces hygroscopicus 155
    Antibiotiki i khimioterapiia = Antibiotics and chemoterapy [sic], 1992
    Co-Authors: Ivanova, Tishkov Skh
    Abstract:

    The influence of protoplasting and protoplast regeneration in the presence of polyethylene glycol on antibiotic activity, components of antibiotic complexes and antibiotic resistance in Streptomyces hygroscopicus 155 was studied. It was shown that the protoplasting and protoplast regeneration influenced the antibiotic activity. The protoplast fusion resulted in increased isolation of variants with higher antibiotic activity. The processes also affected the components of the antibiotic complexes but had no effect on the strain resistance to some antibiotics.

Huang Wei-yi - One of the best experts on this subject based on the ideXlab platform.

C. Richard Hutchinson - One of the best experts on this subject based on the ideXlab platform.