Abstract
The presence of optimal concentrations of Mn 2+ , Mg 2+ (0.5 mM), and Ca 2+ (3 m M) in the culture medium avoided the premature stoppage of growth and alginate biosynthesis in Pseudomonas aeruginosa and stimulated alginate synthesis. Their role as potential mediators in the control of alginate biosynthesis by a high mucoid P. aeruginosa strain appeared not to be attributable to the activation of the synthesis of phosphomannose isomerase (PMI), phosphomannomutase (PMM), GDP-mannose pyrophosphorylase (GMP), or GDP-mannose dehydrogenase (GMD), the enzyme leading to the synthesis of GDP-mannuronic acid, the precursor for polymerization in the alginate pathway. The effect of Mn 2+ , Mg 2+ , and Ca 2+ , as possible activators, was studied in crude extracts of recombinant cells, presenting high enzymatic levels by the overexpression of alginate cloned genes. Mn 2+ and Mg 2+ (range 0–20 m M) led to the increase of the enzyme activities assayed in vitro of GMD and PMI, whereas PMM was only activated by Mn 2+ .
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