Browsing by Author "Chase, Howard A"

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    The effect of culture history on the disruption of Alcaligenes eutrophus by high pressure homogenisation
    (Springer Netherlands, 1990) Harrison, Susan T; Dennis, John S; Chase, Howard A
    To date, rigorous study of the use of high pressure homogenisation in cell rupture over a wide range of operating conditions has been confined to the yeasts. This investigation concentrates on the rupture of the Gram-negative bacterium Alcaligenes eutrophus by an industrial homogeniser. The parameters affecting cell disruption such as operating pressure, temperature and biomass concentration as well as the effect of cell characteristics such as growth rate, size, shape and wall strength were studied. Bacterial cultures which are growing rapidly in the logarithmic phase exhibit less resistance to rupture than nutrient limited cultures in the stationary phase. This is accompanied by a decreased dependence of the degree of cell rupture on operating pressure with increased culture age. The extent of accumulation of the storage product poly-β-hydroxybutyrate during stationary phase has a less significant effect on the resistance to cell rupture than the growth phase of the microorganism. This is particularly interesting owing to the concomitant change in the shape and size of the bacterium on the accumulation of storage product. A variety of chemical and physical treatments of the stationary phase micro-organisms prior to rupture have been considered in an attempt to decrease cell wall strength. Cell rupture efficiency is increased by any of the following pretreatments: incubation at 45°C, alkaline pH shock, addition of the detergent sodium dodecyl sulphate or addition of sodium chloride.
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    The lysis of Gram-negative Alcaligenes eutrophus by enzymes from Cytophaga
    (Springer Verlag, 1991) Harrison, Susan T L; Chase, Howard A; Dennis, John S
    The use of Cytophaga lysing enzymes was investigated for the liberation of poly-~- hydroxybutyrate (PHB) granules from the Gram-negative bacterium AlcaIigenes eutrophus. Complete cell lysis was approached within a 60 minute period. Contrary to previous findings for the lysis of Gram-negative bacteria, prior removal of the outer membrane was not essential for enzymic lysis. The destabilisation of the outer membrane by the removal of divalent cations resulted in no significant improvement in the disruption process.
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    The plasticisation of polyhydroxybutyrate in vivo
    (Elsevier, 1992) Harrison, Susan T L; Chase, Howard A; Amor, Stuart R; Bonthrone, Karen M; Sanders, Jeremy K M
    The influence of a variety of treatments on the mobility and crystallinity of poly(hydroxybutyrate) (PHB) in whole cells and native granules has been proved using 13C-n.m.r. spectroscopy and X-ray powder diffraction, and correlated with the known biological effects of these treatments. It was concluded that at least water is responsible for PHB plasticization in vivo, and that only native mobile PHB is susceptible to depolymerases. Another, probably hydrophobic, component appears to be involved either as plasticizer or nucleation inhibitor. Three states of the granule are identified in addition to the native, biologically-competent state: freeze-drying of whole cells leads to a partially-immobilized amorphous state which can be restored virtually to native mobility by rehydration; extended centrifugation of native granules in aqueous suspension, or treatment with hydrophobic detergents under certain conditions, leads to a crystalline state that is less susceptible to exogenous depolymerase; and heating to 95 degrees C or refrigeration has no detectable effect on mobility but leads to inactivation of the granule, presumably via damage to superficial membrane or protein.