Leptothoe, a new genus of marine cyanobacteria (Synechococcales) and three new species associated with sponges from the Aegean Sea.

Cyanobacterial diversity associated with sponges remains underestimated, though it is of great scientific interest in order to understand the ecology and evolutionary history of the symbiotic relationships between the two groups. Of the filamentous cyanobacteria, the genus Leptolyngbya is the most frequently found in association with sponges as well as the largest and obviously polyphyletic group. In this study, five Leptolyngbya-like sponge-associated isolates were investigated using a combination of molecular, chemical, and morphological approach and revealed a novel marine genus herein designated Leptothoe gen. nov. In addition, three new species of Leptothoe, Le. sithoniana, Le. kymatousa, and Le. spongobia, are described based on a suite of distinct characters compared to other marine Leptolyngbyaceae species/strains. The three new species, hosted by four sponge species, showed different degrees of host specificity. Leptothoe sithoniana and Le. kymatousa hosted by the sponges Petrosia ficiformis and Chondrilla nucula, respectively, seem to be more specialized than Le. spongobia, which was hosted by the sponges Dysidea avara and Acanthella acuta. All three species contained nitrogen-fixing genes and may contribute to the nitrogen budget of sponges. Leptothoe spongobia TAU-MAC 1115 isolated from Acanthella acuta was shown to produce microcystin-RR indicating that microcystin production among marine cyanobacteria could be more widespread than previously determined.