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Effects of growth-inhibitory concentrations of copper on alginate biosynthesis in highly mucoid Pseudomonas aeruginosa

Laboratório de Engenharia Bioquímica, Centro de Engenharia Biológica e Química, Instituto Superior Técnico, Av. Rovisco Pais, 1096 Lisboa Codex, Portugal

²Author for correspondence: Isabel Sá-Correia. Tel: +351 1 8417682. Fax: +351 1 S480072. e-mail: qisc@beta.ist.utl.pt

ABSTRACT

Alginate production and degree of polymerization were affected when the highly mucoid Pseudomonas aeruginosa 8821M was grown with growth-inhibitory concentrations of Cu²⁺ (supplied as CuCl₂; 1-5 mM). The inhibition of alginate biosynthesis was consistent with the decreased activity in Cu²⁺-stressed cells of phosphomannose isomerase/GDP-mannose pyrophosphorylase (encoded by algA), phosphomannomutase (encoded by algC) and GDP-mannose dehydrogenase (encoded by algD). However, in cells grown with concentrations of CuCl₂ below 2 mM, the steady-state mRNA levels from algA, algC, algD and from the regulatory gene algR1 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 Cu²⁺ 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 Cu²⁺-grown cells was correlated with changes in gene expression, with the inhibitory effect of Cu²⁺ on enzyme activities and with Cu²⁺-induced oxidative inactivation of enzymes, especially the particularly sensitive phosphomannose isomerase activity.

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