Genome sequences of bacteria closely associated with the dominant Nostocales cyanobacteria of recent HABs in the US Pacific Northwest

We have assembled over a dozen genomes of bacteria that remained attached after filtration and/or washing to cyanobacterial material derived from recent blooms in freshwater lakes in the US Pacific NW. PacBio and Illumina metagenomes were generated from samples, and when sufficient sequencing reads from heterotrophic bacteria were present to allow genome assembly, those reads typically represented one or at most three distinct bacteria, whose reads were present at levels lower than those of the cyanobacterium. We interpret these genomes as representing phycosphere bacteria. The taxonomic groups represented were diverse, including alphaproteobacteria, betaproteobacteria, Bacteroidetes, Verrucomicrobia, Planctomycetes, Gemmatimonadetes and Vampirovibrionales. These were associated with a range of Nostocales ADA clade cyanobacteria. Typically, there were no close relatives of the new genomes in the genome or 16S rRNA database. In addition to these, a dominant cyanobacterium genome, Dolichospermum sp. DET69, was assembled from 5 samples from Detroit Reservoir, Oregon, taken across 4 years. From each sample, a near-identical Opitutus sp. genome was assembled. This suggests a recurring and specific interaction, perhaps one that survives the boom/bust cycle of over-wintering, after which an emerging bloom arises from a few surviving filaments or from newly germinated akinetes.