Identification of key carbon-fixation pathways and underlying genes for higher CO₂ fixation of mangrove-associated...

Mangrove systems are major blue-carbon reservoirs, storing 4.4 to 11.7 petagrams of organic carbon globally and supporting diverse microalgal communities that drive primary productivity and coastal carbon cycling. The Sundarban, one of the world's largest (3,629.57 km²) mangrove-dominated coastal systems, holds a substantial carbon stock (26.62 Tg). Rising salinity and anthropogenic pressure are altering the diversity of microalgal communities, highlighting the importance of identifying resilient taxa capable of sustaining carbon fixation. To address this need, we conducted whole-genome metagenomic profiling of degraded mangrove soils. The data revealed six dominant microalgal taxa adapted to prevailing salinity and nutrient stress. These six taxa were subsequently isolated from the same habitats, and a 16-day ambient CO₂ (420 ppm) screening was undertaken to evaluate the specific growth rate and biomass gain of the algae. Among them, three physiologically resilient strains Chlorella sp., Limnospira platensis, and Leptolyngbya boryana were selected for controlled CO₂-enrichment concentrations (0.04%, 0.05%, 0.20%, 10%) to mimic future climate change scenarios. Among those microalgae, the Leptolyngbya boryana showed the highest biomass yield (1.31 g L^-1), carbon content (0.52 g C g^-1 dry weight), and CO₂-fixation rate (up to 149 mg CO₂ L^-1 d^-1). Metagenomic analysis further identified that L. boryana possessed the strongest representation of carbon-fixation pathways like Calvin-Benson-Bassham (CBB) cycle and the reductive TCA (rTCA) cycle, regulated by enriched key genes such as cbbL, cbbS, gap2, zwf, and accC. Therefore, this result positions L. boryana as a promising microalgal candidate for carbon sequestration in future CO₂-rich environments under saline coastal ecology.

The online version contains supplementary material available at 10.1007/s13205-026-04986-7.