George P Sharples

Liverpool John Moores University, Liverpool, ENG, United Kingdom

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Publications (8)13.53 Total impact

  • Paul A Hoskisson, George P Sharples, Glyn Hobbs
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    ABSTRACT: Micromonospora echinospora differentiates in both submerged and surface cultures producing abundant dark spores after a period of vegetative mycelial growth. In submerged batch cultures, under either carbon or nitrogen limiting conditions, protease activity was found to coincide with sporulation indicating a relationship between proteolytic activity and differentiation in this organism. Further evidence for this link was provided from surface grown cultures wherein sporulation was inhibited by the serine protease inhibitors TLCK and TPCK. The association between proteolysis and differentiation apparent in this organism correlates with evidence of a similar phenomenon observed in the streptomycetes, suggesting that this may be a common response associated with differentiation in filamentous actinomycetes.
    Antonie van Leeuwenhoek 02/2006; 89(1):191-5. DOI:10.1007/s10482-005-9001-6 · 2.14 Impact Factor
  • Paul A Hoskisson, Reg England, George P Sharples, Glyn Hobbs
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    ABSTRACT: The growth of Micromonospora echinospora was studied in high and low C/N ratio medium using both batch and continuous culture. Asparagine was consumed rapidly in batch cultures where it served as both a nitrogen and carbon source. Glucose consumption was low suggesting that asparagine functions as the major carbon source under these conditions. The effect of nutrient limitation on the accumulation of storage carbohydrate in batch culture revealed an intimate association between nitrogen limitation and the accumulation of carbonaceous reserves. This study revealed that glycogen constituted the major carbohydrate reserve associated with the onset of sporulation. Intracellular trehalose levels were found to be relatively low and may have been affected by the availability of carbon. Continuous culture studies revealed a correlation between glycogen accumulation and increasing growth rate. It was also found that elevated cellular ATP levels correlated with the increase in glycogen, and reduced glycolytic activity. At the higher growth rates cellular ATP levels were elevated and coincided with reduced activity of the key glycolytic enzyme, phosphofructokinase, suggesting that glycogen can act as a convenient energy reservoir when excess carbon flux dictates.
    Antonie van Leeuwenhoek 10/2004; 86(3):225-33. DOI:10.1023/B:ANTO.0000047920.48459.63 · 2.14 Impact Factor
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    P A Hoskisson, G P Sharples, G Hobbs
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    ABSTRACT: This study set out to investigate the effect of amino acids on the uptake of glucose by Micromonospora eichinospora (ATCC 15837). The specific rate of glucose uptake was found to be reduced when organic nitrogen components were present in the medium. Radioactive uptake studies revealed that the Km for glucose in this organism was 53 mm, indicating a low affinity for uptake compared with other actinomycete sugar transport systems. Individual amino acids negatively influenced the rate of glucose transport, suggesting a relationship between amino acid metabolism and glucose uptake in this organism. The sugar transport system was found to be an active process being inhibited by ionophores and KCN. The data suggest a direct link between amino acid metabolism and glucose uptake at the level of sugar transport. This study shows that the uptake of glucose, a major carbon source for many antibiotic fermentations, is significantly reduced in the presence of amino acids. This fact should inform the medium design and feeding regimes of fermentations involving similar actinomycetes.
    Letters in Applied Microbiology 02/2003; 36(5):268-71. DOI:10.1046/j.1472-765X.2003.01306.x · 1.75 Impact Factor
  • Paul A Hoskisson, Glyn Hobbs, George P Sharples
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    ABSTRACT: The physiology of the actinomycete Micromonospora echinospora was examined during growth. Biphasic accumulation of glycogen occurred, initially during the early exponential growth phase, and again following the onset of sporulation at 120 h. Lipid levels increased during growth eventually representing 25% of the cell mass. A significant proportion of the lipid was found to be in the form of triacylglycerols, which were found to accumulate markedly during the sporulation phase. The disaccharide trehalose was also found to accumulate during growth with levels rising to 5% of the dry weight during the mycelial production phase, then remaining constant during sporulation. Antibiotic was produced transiently by the cultures over the period preceding sporulation.
    Canadian Journal of Microbiology 03/2001; 47(2):148-52. DOI:10.1139/w00-137 · 1.18 Impact Factor
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    ABSTRACT: Multiple intracellular proteases were produced by Streptomyces coelicolor throughout growth as surface cultures. Zymography revealed two constitutive, gelatinolytic proteases of approximate molecular masses 32.5 and 36.5kDa. In addition, transient expression of a large (183.5kDa) protease preceded aerial mycelium formation and following this, during sporulation, an additional protease of mass 27.5kDa was produced.
    Biotechnology Letters 01/2001; 23(3):185-187. DOI:10.1023/A:1005603201902 · 1.74 Impact Factor
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    P A Hoskisson, G Hobbs, G P Sharples
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    ABSTRACT: The effects of heat treatment on spores of the actinomycete Micromonospora echinospora were investigated. The percentage of culturable spores in untreated spore stocks was found to be approximately 20%. A 60 degrees C treatment of spores in phosphate buffer for 10 min led to an approximately five-fold increase in the number of culturable units. This indicated that a large proportion of the spores were constitutively dormant. Within 10 min and in the absence of an external energy-yielding substrate, the heat treatment was found to stimulate spore respiration suggesting that endogenous storage compounds were being utilized. Heating spores at 70 degrees C shortened the time period required for activation; holding times greater than 10 min, however, resulted in a reduction of culturable cells. Classic thermal death characteristics were seen at temperatures of 80 degrees C and above with D-values of 21.43, 2.67, 0.45 and 0.09 min being recorded at 70, 80, 90 and 100 degrees C, respectively. Spores of this organism, while being weakly heat resistant in comparison with bacterial endospores, are significantly more resistant than vegetative cells.
    Letters in Applied Microbiology 03/2000; 30(2):114-7. DOI:10.1046/j.1472-765x.2000.00680.x · 1.75 Impact Factor
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    Atul Karandikar, George P Sharples, Glyn Hobbs
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    ABSTRACT: The life cycle of Streptomyces coelicolor during development on solid medium has been studied from a physiological perspective. A biphasic growth pattern was demonstrated, evidenced by a continuous transition from an initial exponential growth period into a slower phase of biomass accretion. The switch between the two phases coincided with the exhaustion of nitrate from the medium. The depletion of nitrate from the medium coincided with the initiation of aerial mycelium formation within the cultures and the development of hydrophobic surface properties. During secondary growth, cultures remained metabolically active, continuing to accumulate DNA, despite a cessation in the levels of RNA and cell protein accretion. In addition, the accumulation of glycogen and lipid contributed to the observed accretion of biomass in this phase. The depletion of nitrate also marked an increase in the production of a-ketoglutarate by the culture and a coincident decrease in medium pH. Latter stages of the secondary growth phase saw the development of spores within the culture, this in turn was associated with a decrease in cellular glycogen. This supported previous observations that glycogen degradation and spore maturation were intimately associated.
    Microbiology 11/1997; 143:3581-3590. DOI:10.1099/00221287-143-11-3581 · 2.84 Impact Factor
  • Atul Karandikar, George P. Sharples, Glyn Hobbs
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    ABSTRACT: Reproducible sporulation using solid-plate cultures ofStreptomyces coelicolor A3(2) was obtained on a defined medium with glucose as the primary source of carbon and sodium nitrate as the sole source of nitrogen. The type of agar used as a solidifying agent, and the inclusion of trace salts to the medium, significantly affected sporulation. An interrelationship between the medium carbon to nitrogen ratio and sporulation was observed, with clear promotion of spore formation under nitrogen-limited conditions, whilst carbon-limited conditions suppressed sporulation. The influence of medium phosphate upon sporulation is also reported, with high concentrations exerting an inhibitory effect.
    Biotechnology Techniques 01/1996; 10(2):79-82. DOI:10.1007/BF00765186