Growing human activities, rapid industrialization and aggressive agricultural activities (use of pesticides etc.) have resulted in a significant increase in the concentration (accumulation) of heavy metals like Cadmium in different ecosystems. Experts believe that this poses a serious threat to the growth of living organisms, especially photosynthetic organisms (cyanobacteria and plants), as the structural and functional aspects of photosynthesis are extremely sensitive to heavy metals. In simpler words, the enhanced stress of Cadmium adversely impacts the productivity of plants/crops. This could in the longer run, add to the concerns of food security, already escalated by climate change situations. Interestingly, cyanobacteria (blue green algae), a significant class of photosynthetic prokaryotes that first appeared on earth at least 2.6 billion years ago when environmental conditions were harsh, are comparatively resistant to heavy metals. A study by researchers from the Department of Botany, Institute of Science, Banaras Hindu University, have made a milestone discovery in this regard. 

The team led by Dr. Yogesh Mishra, Assistant Professor, Botany, and Akanksha Srivastava and Subhankar Biswas, both pursuing their Ph.D. under the supervision of Dr. Mishra, attempted to understand how cyanobacteria maintain their photosynthesis under stressful conditions, particularly in the presence of heavy metals. The process of photosynthesis has two modes: linear electron flow and cyclic electron flow. The enhanced accumulation of cadmium concentration adversely affects the linear electron flow. The research team observed that in case of highly toxic heavy metal cadmium stress in a model cyanobacterium, Anabaena sp. PCC 7120, while linear electron flow gets affected, the cyclic electron flow gets activated in order to maintain the photosynthetic process. The research further resulted in a breakthrough finding with the team revealing that LexA protein regulates these photosynthetic responses by regulating related key photosynthetic genes. This is the first such discovery so far in this regard. 

Dr. Yogesh Mishra said the finding is a result of a detailed study carried out over the years. The latest finding has been published in the globally reputed scientific journal BBA-Proteins and Proteomics (January 2023). The work is expected to pave the way for further research in order to address the challenges of heavy metal toxicity in the ecosystem. It could also help in developing stress tolerant crops with improved photosynthesis efficiency, eventually helping in dealing with the question of food security, he added. “Since photosynthesis is one of the vital processes that is affected by heavy metal stress, our findings are promising for the development of recombinant cyanobacteria with improved photosynthetic efficiency and heavy metal tolerance capacity”, said Dr. Mishra. 

Previous works of the series were published in reputed peer-reviewed journals Environmental and Experimental Botany (2022) and Algal Research (2021). These studies funded by the Department of Atomic Energy, Government of India, were carried out as a joint collaboration between Banaras Hindu University and Bhabha Atomic Research Center (BARC). Other members of the research team include Dr. Hema Rajaram and Dr. Arvind Kumar, from BARC.