Exploring the synergistic effect of Pseudomonas monteilii on the growth promotion of mangrove isolated cyanobacterium Leptolyngbya lignicola.

Mangrove ecosystems host complex microbial interactions that remain insufficiently explored. This study investigates the growth-promoting interaction between the cyanobacterium Leptolyngbya lignicola and the associated bacterium Pseudomonas monteilii isolated from mangrove waters of Bhitarkanika, Odisha, India. Morphological, biochemical, and scanning electron microscopic analyses confirmed a close physical association between the two partners. Under this condition, the co-culture achieved a maximum biomass of 298.19 mg L⁻¹ on the sixth day of incubation, significantly exceeding that of axenic L. lignicola cultures (198.08 mg L⁻¹ on the ninth day) while reducing the cultivation period required to reach the stationary phase. The enhanced growth was accompanied by increased accumulation of photosynthetic pigments, including chlorophyll a, carotenoids, and phycocyanin, as well as elevated levels of proteins, carbohydrates, reducing sugars, and amino acids. Metabolite profiling revealed the production of several growth-promoting compounds by P. monteilii, including indole-3-acetic acid (IAA), indole-3-butyric acid (IBA), vitamin B₁₂, and siderophores. The findings highlight a synergistic interaction that may contribute to improved cyanobacterial productivity in natural systems, leading to algal blooms. This study provides insight into cyanobacteria-bacteria associations in mangrove ecosystems and their potential biotechnological applications.