Genomic Characterization of Filamentous Cyanobacteria on Nantucket Beaches

This report was submitted in fulfillment of a 2014 grant from the Nantucket Shellfish Association and the Nantucket Biodiversity Initiative.

A benthic, epiphytic cyanobacterium has been recently reported as invasive in temperate coastal beaches of the Nantucket Island, Massachusetts, USA, during late summer. Microscopic and molecular analyses were applied to identify the cyanobacterium and describe its phylogenetic position, and to characterize the microbial communities associated with it. The morphological observations in parallel with 16S rRNA and nifH results suggest that the cyanobacterium is closely related to Hydrocoleum sp. (Oscillatoriales, Phormidiaceae), with the closest previously described relative Hydrocoleum lyngbyaceum, and appears to represent a unique strain. The genus is a ubiquitous benthic cyanobacterium in tropical and subtropical waters and coral reefs, where it is at times considered a nuisance, while these observations in North Atlantic temperate waters may represent an expansion of its habitat range. Amplicon sequencing targeting the nifH gene confirmed that the cyanobacterium is capable of fixing N2, and also hosts a relatively diverse community of nifH-gene containing bacteria typifying microbial mat diazotroph communities growing in association with it. Hydrocoleum was recently reported to be a potential producer of homoanatoxin-a, a neurotoxin, but genes for these toxins were not detected in the communities investigated in this study. Increasing sea surface temperatures in the North Atlantic Ocean may have contributed to this potential expansion of Hydrocoleum sp. habitat range.