EVIDENCE FOR A ROLE FOR L-PROLINE AS A SALINITY PROTECTANT IN THE CYANOBACTERIUM NOSTOC-MUSCORUM

Nostoc muscorum required an active proline oxidase in order to assimil ate exogenous proline as a source of fixed nitrogen. A mutant strain ( Ac-r) resistant to growth inhibition by L-azetidine-2-carboxylate (AC) was found to be deficient in proline oxidase activity, and to be a pr oline overaccumulator. Proline overaccumulation, resulting either from mutational acquisition of the Ac-r phenotype or from salinity-inducib le uptake of exogenous proline, conferred enhanced salinity tolerance in this cyanobacterium.