High-throughput DNA sequencing reveals the dominance of pico- and other filamentous cyanobacteria in an urban freshwater Lake.

The current study presents findings related to algal blooms in a fresh water lake, which has been experiencing severe cyanobacterial blooms (CyanoHABs). Primarily, picocyanobacteria belonging to the genus Synechococcus and filamentous cyanobacterial group belonging to Aphanizomenon and Dolichospermum dominated top water column during non-bloom and bloom periods respectively. The dominance of Synechococcus in early summer informs that blooming in Utah Lake starts in early summer and then later is taken over by other bloom-forming cyanobacteria, such as species belonging to the genus Aphanizomenon. A strong negative correlation (r = -0.9, p < 0.001) was found between the occurrence of Aphanizomenon and Synechococcus which correlates very well with the fact that the blooms of these two different cyanobacteria never coexisted. The predominance of cyanobacteria in 2017 was attributed more to temperature (r = 0.18, p < 0.001). The Actinobacteria was negatively correlated with primary production and high chlorophyll a concentration. Flavobacterium and Limnohabitans were the main phytoplankton colonizers and predators detected that could secrete extracellular enzymes to degrade algal exudates (such as proteins and polysaccharides). Additionally, cyanotoxins producers Microcystis aeruginosa and Planktothrix accounted for up to 12.43% and 7.04% of total cyanobacteria abundance during blooms. The relative abundance of chloroplast reads was overall lower than the cyanobacteria reads, except for the May 5th sampling in 2017. There was inter-annual variability in the bloom-associated heterotrophic bacterial populations, but these populations were consistent with bloom-associated bacterial populations found in other lakes. Community diversity analysis for both Shannon and Simpson indices indicated lower community diversity during the bloom period. The beta diversity conducted by PCoA and UPGMA trees suggested the significant temporal rather than spatial impacts on shaping the phytoplankton community structures during the summer season.