Alginate production and degree of polymerization were affected when the highly mucoid 8821M was grown with growth-inhibitory concentrations of Cu (supplied as CuCl; 1-5 m). The inhibition of alginate biosynthesis was consistent with the decreased activity in Cu-stressed cells of phosphomannose isomerase/GDP-mannose pyrophosphorylase (encoded by ), phosphomannomutase (encoded by ) and GDP-mannose dehydrogenase (encoded by ). However, in cells grown with concentrations of CuCl below 2 m the steady-state mRNA levels from and from the regulatory gene increased moderately. This observation is consistent with the suggested linkage between the control of alginate gene expression and the global regulation involved in the oxidative stress response. At highly inhibitory concentrations the levels of the four alginate gene transcripts decreased from maximal values. The bell-shaped curves, representing the effect of Cu concentration on mRNA levels from the four alginate genes, exhibited similar patterns but did not concur. The decrease of the specific activity of enzymes necessary for GDP-mannuronic acid synthesis in Cu-grown cells was correlated with changes in gene expression, with the inhibitory effect of Cu on enzyme activities and with Cu-induced oxidative inactivation of enzymes, especially the particularly sensitive phosphomannose isomerase activity.


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