A new genomic study of Chilika Lake in Odisha has found that fluctuations in salinity and seasonal changes play a decisive role in shaping the composition and functional potential of ‘cyanobacteria’, highlighting the vulnerability of coastal ecosystems to environmental stress.
Cyanobacteria are microscopic organisms that form the backbone of aquatic ecosystems by performing photosynthesis, fixing atmospheric nitrogen and contributing to carbon sink. However, their uncontrolled growth can also trigger harmful algal blooms that threaten fisheries, biodiversity and public health.
Understanding how environmental factors influence these organisms is therefore critical for managing fragile coastal systems, said CSIR-Centre for Cellular and Molecular Biology (CCMB) and LaCONES chief scientist G. Umapathy.
Along with Manisha Ray of the CCMB and Academy of Scientific and Innovative Research (AcSIR), Ghaziabad, he used metagenomic sequencing to analyse genetic material of cyanobacterial communities across seasons and locations in Asia’s largest brackish water lagoon.
The researchers reconstructed 83 cyanobacterial Metagenome-Assembled Genomes (MAGs), enabling them to examine how different lineages and their functional genes respond to changing environmental conditions.
The analysis showed that salinity was the most influential factor shaping cyanobacterial community structure, with additional effects from water transparency, biological oxygen demand, phosphate and silicate levels. Together, these variables explained more than half of the variation in cyanobacterial abundance across the lagoon.
The researchers identified 22 core cyanobacterial taxa that persisted across seasons and sampling sites. These were dominated by the Cyanobiaceae family, including ecologically significant genera such as Cyanobium and Synechococcus. In contrast, around 30 genomes appeared only during specific seasons, with winter 2019 recording an unusually high number of unique taxa, possibly due to nutrient limitation.
The study also reported marked seasonal shifts in genes linked to nitrogen, carbon and phosphate cycling, as well as in pathways associated with toxin production. This suggests that environmental variability influences not just which cyanobacteria dominate the lagoon, but also the ecological functions they perform. Of particular interest was the identification of five genomes carrying genes that point to a previously underappreciated potential for alternative carbon fixation mechanisms in Chilika.
While the study does not directly measure gene activity, the researchers said it offers an important genomic baseline for understanding how environmental changes ”especially shifts in salinity” could reshape cyanobacterial communities. This, they added, could aid future monitoring and management strategies for Chilika and other climate sensitive coastal lagoon. This study has been published in the recent issue of the Environmental Advances journal.