Browsing by Author "Xu, Karen D."

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Gene expression and protein levels of the stationary phase sigma factors, RpoS, in continuously-fed Pseudomonas aeruginosa biofilms
(2001-05) Xu, Karen D.; Franklin, Michael J.; Park, C-H; McFeters, Gordon A.; Stewart, Philip S.
Bacteria growing in biofilms experience gradients of environmental conditions, including varying levels of nutrients and oxygen. Therefore, bacteria within biofilms may enter distinct physiological states, depending on the surrounding conditions. In this study, rpoS expression and RpoS levels were measured as indicators of stationary phase growth within thick continuously-fed Pseudomonas aeruginosa biofilms. The level of rpoS expression in a 3-day-old biofilm was found to be three-fold higher than the average expression in stationary phase planktonic cultures. In planktonic cultures, oxygen limitation did not lead to increased levels of RpoS, suggesting that oxygen limitation was not the environmental signal causing increased expression of rpoS. These results suggest that bacteria within P. aeruginosa biofilms may exhibit stationary phase characteristics even when cultured in flow conditions that continually replenish nutrients.
Physiological heterogeneity and biofilm control," in: biofilms in the aquatic environment
(1999) McFeters, Gordon A.; Stewart, Philip S.; Huang, Ching-Tsan; Wentland, Eric Jon; Xu, Karen D.; Yu, Feipeng Philip
Spatial patterns of alkaline phosphatase expression within bacterial colonies and biofilms in response to phosphate starvation
(1998-04) Huang, Ching-Tsan; Xu, Karen D.; McFeters, Gordon A.; Stewart, Philip S.
The expression of alkaline phosphatase in response to phosphate starvation was shown to be spatially and temporally heterogeneous in bacterial biofilms and colonies. A commercial alkaline phosphatase substrate that generates a fluorescent, insoluble product was used in conjunction with frozen sectioning techniques to visualize spatial patterns of enzyme expression in both Klebsiella pneumoniae and Pseudomonas aeruginosa biofilms. Some of the expression patterns observed revealed alkaline phosphatase activity at the boundary of the biofilm opposite the place where the staining substrate was delivered, indicating that the enzyme substrate penetrated the biofilm fully. Alkaline phosphatase accumulated linearly with time in K. pneumoniae colonies transferred from high-phosphate medium to low-phosphate medium up to specific activities of 50 μmol per min per mg of protein after 24 h. In K. pneumoniae biofilms and colonies, alkaline phosphatase was initially expressed in the region of the biofilm immediately adjacent to the carbon and energy source (glucose). In time, the region of alkaline phosphatase expression expanded inward until it spanned most, but not all, of the biofilm or colony depth. In contrast, expression of alkaline phosphatase in P. aeruginosa biofilms occurred in a thin, sharply delineated band at the biofilm-bulk fluid interface. In this case, the band of activity never occupied more than approximately one-sixth of the biofilm. These results are consistent with the working hypothesis that alkaline phosphatase expression patterns are primarily controlled by the local availability of either the carbon and energy source or the electron acceptor.
Spatial physiological heterogeneity in Pseudomonas aeruginosa biofilm is determined by oxygen availability
(1998-10) Xu, Karen D.; Stewart, Philip S.; Xia, Fuhu; Huang, Ching-Tsan; McFeters, Gordon A.