Whole-genome sequencing and functional characterization of a heterocystous cyanobacterium promoting rice seed...

Cyanobacteria play a pivotal role in the sustainability of rice-based agroecosystems through biological nitrogen fixation and the synthesize of a variety of plant growth-promoting metabolites.In the present study, a heterocyst-forming cyanobacterial strain, Aliinostoc sp. VUB2213, was isolated from rice fields and characterized using a polyphasic approach. Detailed morphological and ultrastructural features were examined using light and transmission electron microscopy, confirming its assignment to the family Nostocaceae. Phylogenetic analysis based on 16 S rRNA gene sequences positioned this isolate within the Aliinostoc clade, suggesting a distinct lineage. Whole-genome annotation identified genes related to phytohormone biosynthesis, stress adaptation, and core metabolic pathways, including auxin-associated loci (ipdC, aldH, and ipt), indicating enzymatic potential relevant to plant growth promotion. Indole-3-acetic acid (IAA) synthesis was confirmed through combined analytical approaches, including TLC, FTIR, and HPLC profiling. Seed germination assays using rice demonstrated significant improvements in germination percentage, early growth traits, including enhanced root and shoot development and improved seedling vigor, in response to treatments with culture supernatant and crude IAA extract. Overall, the genomic and functional traits of Aliinostoc sp. VUB2213 highlight its promise as a bioinoculant for promoting rice growth and contributing to sustainable agricultural practices.