<i>Sphaerothrix gracilis gen.</i> et sp. nov. (<scp>Nodosilineales, Cyanobacteria</scp>): a novel filamentous cyanobacterium isolated from tropical coastal microplastics

SUMMARY Cyanobacteria are ancient organisms that contribute significantly to primary production in aquatic ecosystems. Although they are a group of microbes present in a wide range of environments, their diversity on anthropogenic substrates, namely microplastics, is still largely unknown. In the present study, we describe a new genus and species of cyanobacteria from the Nodosilineaceae family. Strains were isolated from foam microplastic particles obtained from beach sediments facing the Singapore Strait. This species is morphologically similar to the polyphyletic, cosmopolitan Leptolyngbya spp.; however, it forms an independent clade with 16S rRNA phylogeny and has a unique 16S–23S internal transcribed spacer secondary structure. To date, no cyanobacteria have been isolated and cultured from the surfaces of microplastic particles. Using a polyphasic approach combining morphological, phylogenetic and ecological traits, we describe a new genus and species Sphaerothrix gracilis. The presence of certain cyanobacteria rafting on microplastic surfaces can potentially indicate a long‐distance transport into new ecosystems with implications on toxicity and biodiversity.