Maladies mycobactériennes
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Engineering cyanobacteria nitrogen bio-fertilizer for rice cultivation in stressful environment

Shree Kumar Apte

As a naturally abundant, photosynthetic, nitrogen-fixing microbe, the cyanobacterium Anabaena contributes significantly to the nitrogen and carbon economy of tropical soils, especially in cultivation of rice paddy. However, its nitrogen bio-fertilizer potential is adversely affected by common abiotic stresses. Engineering enhanced nitrogen fixation and stress tolerance capabilities in this microbe through genetic manipulation is seriously limited due to the unavailability of appropriate tools and techniques and knowledge of suitable candidate genes. In recent years, our laboratory has devised an electroporation protocol for genetic transformation that achieves high frequency gene transfer and overcomes problems associated with the current practice of triparental conjugation between E. coli strains and Anabaena. We have also constructed (a) a suitable vector for new gene discoveries, and (b) a novel integrative expression vector pFPN, placing desired genes at a defined locus in Anabaena genome and facilitates their high level expression from an eco-friendly light-inducible promoter. Using these tools we have identified several genes responsible for enhanced heterocyst formation and nitrogen fixaton (hetR), chaperones (groESL, cpn60) for protein folding and homeostasis, and several oxidative stress tolerance genes (superoxide dismutases, catalases and peroxiredoxins) which confer superior stress tolerance to Anabaena. The approach has proved very useful for constructing recombinant Anabaena strains capable of nitrogen fixation in stressful environments.