Morphological, genetic and physiological characterization of Hydrocoleum, the most common benthic cyanobacterium in tropical oceans

ABSTRACTPopulations of the benthic diazotrophic cyanobacterium Hydrocoleum Kutzing (1843) are widely distributed in coral reefs and lagoons of tropical oceans, where they contribute to benthic nitrogen fixation. We compared the morphological, molecular and physiological features of 31 freshwater and marine Hydrocoleum populations from geographically different localities and five specimens from herbaria. Our aims were to compare the features of Hydrocoleum with the morphologically and phylogenetically related genera Trichodesmium Ehrenberg ex Gomont 1892 and Blennothrix Kutzing 1843, and to provide the basis for the validity of the genus Hydrocoleum. The Hydrocoleum populations were distributed over a wide range of sizes, showing no consistent inter-population grouping and leaving no gaps between groups that were traditionally attributed to different species. Transmission electron microscopy showed regular cell division rhythms in all Hydrocoleum populations with each cell division completed before the nex...