Kovacikia minuta sp. nov. (Leptolyngbyaceae, Cyanobacteria), a new freshwater chlorophyll f-producing cyanobacterium

A few groups of cyanobacteria have been characterized as having far-red light photoacclimation (FaRLiP) that results from chlorophyll f (Chl f) production. In this study, using a polyphasic approach, we taxonomically transferred the Cf. Leptolyngbya sp. CCNUW1 isolated from a shaded freshwater pond, which produces Chl f under far-red light, to the genus Kovacikia and named this taxon Kovacikia minuta sp. nov. This strain was morphologically similar to Leptolyngbya-like strains. The thin filaments were purplish-brown under white light but became grass green under far-red light. The 31-gene phylogeny grouped K. minuta CCNU0001 into order Synechococcales and family Leptolyngbyaceae. Phylogenetic analysis based on 16S rRNA gene sequences further showed that K. minuta CCNU0001 was clustered into Kovacikia with similarities of 97.2-97.4% to the recently reported type species of Kovacikia muscicola HA7619-LM3. Additionally, the internal transcribed spacer region between 16S-23S rRNA genes had a unique sequence and secondary structure compared with other Kovacikia strains and phylogenetically related taxa. Draft genome sequences of K. minuta CCNU0001 (8,564,336 bp) were assembled into one circular chromosome and two circular plasmids. A FaRLiP 20-gene cluster comprised two operons with the unique organization. In sum, K. minuta was established as a new species, and it is the first species reported to produce Chl f and for which a draft genome was produced in genus Kovacikia. This study expanded our knowledge regarding the diversity of Chl f-producing cyanobacteria in far-red light-enriched environments and provides important foundational information for future investigations of FaRLiP evolution in cyanobacteria.