Heterocyte-forming cyanobacteria play essential roles in carbon, oxygen, and nitrogen cycling within coral reef ecosystems. However, the proliferation of cyanobacterial mats, exacerbated by human activities, nutrient enrichment, and climate change, threatens coral survival by promoting coral diseases and displacing corals in tropical reefs. In this study, we describe Aliinostoc maniaoense sp. nov., a newly discovered heterocyte-forming cyanobacterium isolated from a coral reef in the South China Sea. Through a polyphasic approach, which included morphological analysis, 16S rRNA gene sequencing, and secondary structure analysis of the 16S-23S ITS region, we identified distinct features that set A. maniaoense apart from related species. The large genome of A. maniaoense reveals diverse functional capabilities, which may enhance its ability to adapt and thrive in coral reef environments. The discovery of multiple ribosomal operons in the 16S-23S rRNA ITS region suggests that variations in secondary structure should be carefully considered in cyanobacterial taxonomy. This study advances our understanding of cyanobacterial diversity in tropical marine ecosystems and highlights the importance of using comprehensive datasets for accurate species classification.

marine cyanobacteria, nitrogen fixation, heterocyte-forming,coral reefs, South China Sea