Project description:A screening process was used to determine the aciduric capacities of a diverse set of Listeria monocytogenes strains and was based on the capacity to grow at pH 5.0 in the presence 4 different organic acids. Food and clinical isolates tended to be more resistant but strain genetic groupings were found to be only weakly linked to sodium diacetate (SDA)-resistance. Representative and comparatively aciduric food isolates FW04/0023 and FW04/0025 were found to accumulate reduced levels of acetate anion and K+ ion during growth in the presence of SDA, compared to more acid sensitive reference strains EGD (ATCC BAA-739) and ATCC 19111. The aciduric nature of FW04/0023 and FW04/0025 was also reflected by their comparatively high tolerance to pH 2.4 acid challenge; a property boosted by the presence of SDA, and growth-phase dependent acid tolerance. Transcriptomic analyses revealed increased levels of SDA did not activate or promulgate the response of any of the known acid protective mechanisms, except for acetoin biosynthesis. Elevated levels of unprotonated SDA (20 mM SDA at pH 5.0) was found to have broad effects on gene expression that could be differentiated from effects caused by mildly acidic conditions (pH 5.0) and substantial strain variation was also found. Collated SDA mainly effect genes associated with virulence, cell wall processes, DNA repair, and cofactor and lipid biosynthesis. Strain FW04/0025 was more responsive to elevated unprotonated SDA increasing the expression of 222 genes (>2-fold change, p<0.05), compared to 112 genes for strain EGD. Key differences between the strains in relation to SDA-enhanced transcript abundance in FW04/0023 were primarily associated with the cell wall, oxidative stress management, intermediary metabolism, and several hypothetical proteins. This complement of different responses could potentially alter phenotypes resulting in different cell envelope properties and metabolic properties that effect accumulation of acetate anion. The data demonstrates that amongst different L. monocytogenes strains acetate has differing effects that may ultimately influence growth efficiency under stressful conditions relevant to acidic foods and the gastrointestinal environment. The microarray component of the experiments had the aim of determining: i) To examine the affect of elevated levels of unprotonated sodium diacetate (21 mM sodium diacetate added to cultures at pH 5.0, resulting in ~7.7 mM unprotonated acetate) compared to mild acid stress at pH 5.0 in which lower levels of acetate accumulates through natural end-product formation. ii) To examine the gene expression responses of two L. monocytogenes strains that had different intrinsic acid resistances, including an organic acid resistant strain FW04/0025 and a more sensitive reference strain EGD on which genome the microarray oligonucleotide set is based.

Project description:A screening process was used to determine the aciduric capacities of a diverse set of Listeria monocytogenes strains and was based on the capacity to grow at pH 5.0 in the presence 4 different organic acids. Food and clinical isolates tended to be more resistant but strain genetic groupings were found to be only weakly linked to sodium diacetate (SDA)-resistance. Representative and comparatively aciduric food isolates FW04/0023 and FW04/0025 were found to accumulate reduced levels of acetate anion and K+ ion during growth in the presence of SDA, compared to more acid sensitive reference strains EGD (ATCC BAA-739) and ATCC 19111. The aciduric nature of FW04/0023 and FW04/0025 was also reflected by their comparatively high tolerance to pH 2.4 acid challenge; a property boosted by the presence of SDA, and growth-phase dependent acid tolerance. Transcriptomic analyses revealed increased levels of SDA did not activate or promulgate the response of any of the known acid protective mechanisms, except for acetoin biosynthesis. Elevated levels of unprotonated SDA (20 mM SDA at pH 5.0) was found to have broad effects on gene expression that could be differentiated from effects caused by mildly acidic conditions (pH 5.0) and substantial strain variation was also found. Collated SDA mainly effect genes associated with virulence, cell wall processes, DNA repair, and cofactor and lipid biosynthesis. Strain FW04/0025 was more responsive to elevated unprotonated SDA increasing the expression of 222 genes (>2-fold change, p<0.05), compared to 112 genes for strain EGD. Key differences between the strains in relation to SDA-enhanced transcript abundance in FW04/0023 were primarily associated with the cell wall, oxidative stress management, intermediary metabolism, and several hypothetical proteins. This complement of different responses could potentially alter phenotypes resulting in different cell envelope properties and metabolic properties that effect accumulation of acetate anion. The data demonstrates that amongst different L. monocytogenes strains acetate has differing effects that may ultimately influence growth efficiency under stressful conditions relevant to acidic foods and the gastrointestinal environment. The microarray component of the experiments had the aim of determining: i) To examine the affect of elevated levels of unprotonated sodium diacetate (21 mM sodium diacetate added to cultures at pH 5.0, resulting in ~7.7 mM unprotonated acetate) compared to mild acid stress at pH 5.0 in which lower levels of acetate accumulates through natural end-product formation. ii) To examine the gene expression responses of two L. monocytogenes strains that had different intrinsic acid resistances, including an organic acid resistant strain FW04/0025 and a more sensitive reference strain EGD on which genome the microarray oligonucleotide set is based. Two to four biologically replicated control cultures were labelled with Cy3 for each treatment sample with two sets of experimental conditions investigated for two different L. monocytogenes strains . Condition 1) â Mildly acidic stress: Control culture (Cy3-labelled RNA) - strains were grown to early- mid exponential growth phase at 25Â°C (in a shaking water bath) in brain-heart infusion broth at pH 7.3. Test cultures (Cy5-labelled RNA) â strains grown to early- mid exponential growth at 25Â°C phase in BHI broth adjusted to pH 5.0 (in a shaking water bath). Condition 2) â Organic acid (sodium diacetate) stress: Control culture (Cy3-labelled RNA) - strains were grown to exponential growth phase at 25Â°C (in a shaking water bath) in BHI broth at pH 5.0. Test cultures (Cy5-labelled RNA) â strains grown to exponential growth at 25Â°C phase in BHI broth adjusted to pH 5.0 and amended with 21 mM (0.3% w/v)sodium diacetate (in a shaking water bath).

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Deletion of the Aspergillus niger pro-protein processing protease gene kexB results in a pH-dependent morphological transition during submerged cultivations and increases cell wall chitin content

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