Browsing by Author "Palmer, Carl J"

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    The effect of nutrient limitation and oxidative stress on bromoform production from axenic cultures of marine diatoms
    (2012) Nguvava, Mariam; Bucciarelli, Eva; Waldron, Howard; Palmer, Carl J
    Bromoform is mainly produced naturally by marine organisms. The production by microalgae however is not well quantified, and the mechanism by which phytoplankton produce bromoform is not fully elucidated. The production of this compound at the cellular level seems to be linked to oxidative stress via the use of the antioxidant enzyme bromoperoxidase (Manley and Barbero, 2001). However, no experiment has been conducted under bacteria-free conditions, which may bias the results because bacteria produce bromoform. Diatoms, which are wide spread in the open ocean, could be amongst the most important producers of bromoform. The purpose of this study was to quantify the effect of nutrient limitation and oxidative stress on bromoform production from axenic cultures of marine diatoms.
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    An investigation into source and distribution of bromoform in the Southern African and Southern Ocean Marine boundry layer
    (2014) Kuyper, Brett; Reason, Chris; Waldron, Waldron, Howard; Palmer, Carl J; Labuschagne, Casper
    Bromoform is a climatically important atmospheric trace gas. It is released by macro- and microalgae into the ocean, and rapidly transferred to the atmosphere, where bromoform undergoes rapid photolysis yielding bromine radicals. These bromine radicals are known to participate in catalytic destruction of ozone at all levels throughout the atmosphere. This is especially important in the lower stratosphere. This destruction of ozone results in changes in the oxidative potential and decreases the greenhouse effect of the troposphere. A task-specific gas chromatograph with electron capture detector system, developed in-house, was used for the separation and quantitative detection of bromoform mixing ratios from environmental air samples. A custom thermal desorption unit was designed and built for use in this system along with a graphical user interface for the real-time collection and display of data. A limit of detection of 0.79 ± 0.09 ppt, with an overall precision of 12.7 % was achieved with this GC system and method. The quantitative detection of bromoform mixing ratios was made at the Cape Point, Global Atmospheric Watch station over a one month period in early spring 2011. Bromoform mixing ratios detected ranged between 2.29 and 84.7 ppt with a mean of 24.7 ppt. These mixing ratios appear to be generally elevated compared to previous studies, however, were still within the maximum values published. Local kelp beds around Cape Point and possibly anthropogenic inputs from Cape Town are likely to have been the dominant source of bromoform measured there, caused by changes in wind speed. A series of experiments were performed to explore the role of the bromoperoxidase enzyme in providing antioxidant protection in two diatom species (Phaeodactylum tricornutum and Chaetoceros neogracile_cf ) under different oxidative stresses. Carbon dioxide and nitrate limitation were induced as oxidative stresses. The mean per cell bromoform concentrations during the growth phase of the carbon limitation were 2.73 x 10¯¹⁷ and 8.68 x 10¯¹⁸ mol cell¯¹ for C. neogracile_cf and P. tricornutum, respectively. This decreased to 2.94 x 10¯¹⁸ and 3.87 x 10¯¹⁸ mol cell¯¹ during the limited phase. Bromoform production decreased to zero for P. tricornutum during the nitrate limitation. These experiments suggest that in these species bromoperoxidase is not utilised as an antioxidant pathway when under these nutrient limiting conditions.