1887

Abstract

Within certain infection sites, such as the lung of cystic fibrosis patients, grows statically under either decreased oxygen tension or anaerobic conditions, a situation that is likely to influence the production of virulence factors. The goal of this study was to determine the effect of static growth under microaerobic (decreased oxygen) and anaerobic conditions on the expression of the exotoxin A (ETA) gene and its positive regulator . Using and fusion plasmids, the level of and expression was measured throughout the growth cycle of strain PAO1, which was grown in either iron-deficient or iron-sufficient medium under four different conditions: 20 %-SH (aerobic, shaking), 20 %-ST (aerobic, static), 10 %-ST (microaerobic, static) and 0 %-ST (anaerobic, static). In iron-deficient medium, expression was higher under 20 %-ST and 10 %-ST than under 20 %-SH. However, the highest level of expression occurred under 0 %-ST. Analysis of ETA protein using sandwich ELISA revealed that at time points between 8 and 24 h of the growth curve, PAO1 produced higher levels of ETA under 0 %-ST than under 20 %-SH. In iron-sufficient medium, expression was significantly repressed under all conditions. Additional analyses using PAO1 strains that carry fusions with the regulatory genes and revealed that the expression of and is reduced rather than increased at 0 %-ST. expression under different conditions paralleled that of expression, except that it was repressed by iron under 20 %-SH only. Between 6 and 24 h of growth, and under all conditions, the level of dissolved oxygen (DO) within the PAO1 cultures was sharply reduced. These results suggest that (1) the combined effect of static growth and anaerobic conditions produce a significant increase in and expression in PAO1; (2) this effect appears to be unique to and , since the level of and expression was reduced under the same conditions; (3) neither static growth nor anaerobic conditions interfere with the repression of expression by iron, although static growth deregulates expression with respect to iron; and (4) the enhanced expression of and is not related to the reduced levels of DO in PAO1 cultures.

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2005-07-01
2024-04-23
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