Isolation and characterization of heterocytes cyanobacteria and investigating their role in enhancing seed germination

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Abstract
Cyanobacteria, as vital photosynthetic microorganisms in soil ecosystems, contribute to soil stabilization, nutrient cycling, and water balance. They also produce bioactive compounds such as lipopeptides, carotenoids, and phytohormones. This study explored the plant growth-promoting potential of cyanobacterial strains isolated from native paddy field soils. A polyphasic approach, combining 16S rRNA gene sequencing, phylogenetic analysis, and morphological assessments was used to characterize the isolates. Microscopy revealed distinct traits, including barrel-shaped cells, intercalary and terminal heterocytes, solitary akinetes adjacent to heterocytes, and proakinetes occurring near heterocytes. The strain also displayed a fascicular thylakoid arrangement and contained distinct nutrient storage granules. Phylogenetic analysis placed the isolate in close relation to Neowollea manoromensis. The strain produced an auxin-like compound, identified as indole-3-acetic acid (IAA), under various tryptophan concentrations. IAA was confirmed through TLC, FT-IR, and HPLC. In vitro experiments with paddy seeds treated with cyanobacterial extract showed 95.55% germination, with significant root elongation (11.27 ± 0.09 cm) and shoot growth (6.46 ± 0.050 cm) by day 12. Chlorophyll content (3.18 μg/mL), fresh weight (0.69 ± 0.09 g), and dry weight (0.08 ± 0.00 g) also increased. These results underline the auxin-producing potential of the cyanobacterium and its effectiveness in enhancing seed germination and plant growth, offering a sustainable strategy for improving paddy cultivation.

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