Insight on the heterocyte patterning and the proheterocyte division in the toxic cyanobacterium Kaarinaea lacus gen. nov., sp. nov., and its genomic potential for natural products

Nostoc sp. 152 (= PCC 9237^T), a toxic cyanobacterium, isolated from mixed cyanobacterial bloom in a Finnish freshwater lake was reassessed using phylogenetic, morphological and genomic analyses. Multilocus and 16S rRNA gene phylogenetic analyses confirmed that this strain represents a novel Nostocalean genus for which we propose the name Kaarinaea lacus gen. nov., sp. nov., in accordance with the International Code of Nomenclature of Prokaryotes. The most intriguing morphological feature exhibited by PCC 9237^T is the occasional division of proheterocytes. Based on our observations, we propose a hypothesis for the sequence of events taking place leading to this phenomenon. The other interesting feature includes the unusual heterocyte patterning resulting in the development of heterocytes in series in the old culture followed by its fragmentation at this site. Among the genes involved in heterocyte differentiation and patterning, patC and three homologs of hetP were not found from the genome of PCC 9237^T. Furthermore, genomic investigations revealed a variant of heterocyte glycolipid gene cluster with a reduced hglB, but having additional gene coding for a protein with TubCN terminal docking domain. Finally, the presence of a pks2-like gene cluster, whose product may interfere with the cellular differentiation, and an anachelin-like gene cluster demands further investigations.