Firefly Luciferase Expression on Nitrogen Fixation with Non-Legumes

We have tested the firefly luciferase expression under Rhizobium meliloti symbiotic promoters control in nitrogen fixation bacteria non associated with legumes. Constitutive expression of luc gene was determined in the same bacteria using a fusion to λPR promoter. Luciferase activity was found in all nitrogen fixer backgrowns but it depended of promoter activation conditions. Bioluminiscence was high enough in bacteria containing λpr-luc fusion to be observed by a dark adapted eye and photographed.