Neochroococcus gongqingensis gen. et sp. nov., a new member of coccoid cyanobacteria from a watercourse, Eastern China

The taxonomy of coccoid cyanobacteria has been largely revised in recent years. In this study, a novel coccoid cyanobacterial strain was isolated from a watercourse at the Poyang Lake Model Research Base, Jiangxi province, Eastern China. A polyphasic approach combining morphological and molecular testing was used to characterize this strain referred to as CHAB 4018. Regarding colonial form and cellular spatial arrangement, this strain was morphologically similar to strains of the genus Eucapsis. The maximum 16S rRNA gene sequence similarity of this strain to the currently described cyanobacteria genera was 93.40%, exceeding the cutoff for genus delimitation in bacteriology. Furthermore, a phylogenetic tree based on 16S rRNA gene sequences indicated that strain CHAB 4018 formed a unique clade in the family Chroococcaceae and was phylogenetically close to the recently established genus Cryptococcum but distant from the Chroococcus 'sensu stricto' clade and from Eucapsis. Thus, a novel coccoid cyanobacterial genus with a new species is here described as Neochroococcus gongqingensis. A large phylogenetic tree using more strains suggested phylogenetic intermixture of Chroococcus-like and Eucapsis-like cyanobacteria, suggesting the need for further studies on the phylogeny and taxonomy of coccoid cyanobacteria.