Gluconacetobacter diazotrophicus is a nitrogen-fixing, endophytic bacterium that has the potential to promote plant growth and increase yield. Genetically modified strains might get more benefits to host plants, including through expression of useful proteins, such as Cry toxins from B. thuringiensis, or enzymes involved in phytohormone production, proteins with antagonistic activity for phytopathogens, or that improve nutrient utilization by the plant. For that, expression systems for G. diazotrophicus are needed, which requires active promoters fused to foreign (or innate) genes. This article describes the construction of a G. diazotrophicus PAL5 promoter library using a promoter-less lacZ-bearing vector, and the identification of six active promoters through β-galactosidase activity assays, sequencing and localization in the bacterial genome. The characterized promoters, which are located on distinct regions of the bacterial genome and encoding either sense or antisense transcripts, present variable expression strengths and might be used in the future for expressing useful proteins.
Keywords: Endophytic diazotroph; Plant growth promotion; Promoter trap; Protein expression system.