Sulfolipid substitution ratios of Microcystis aeruginosa and planktonic communities as an indicator of phosphorus limitation in Lake Erie

Phosphorus (P) availability frequently limits primary production in lakes, influences the physiology of phytoplankton, shapes community structure, and can stimulate or constrain the formation of cyanobacterial blooms. Given the importance of P, numerous methods are available to assess P stress in phytoplankton communities. Marine phytoplankton are known to substitute sulfolipids for phospholipids in response to P limitation. We asked whether sulfolipid substitution might serve as an additional indicator of P stress in freshwater phytoplankton communities. The question was addressed using cultures of Microcystis aeruginosa, Lake Erie microcosms, and surveys of lipid profiles in Lake Erie during a Microcystis spp. bloom. Peak area response ratios of the intact polar lipids sulfoquinovosyldiacylglycerol (SQDG) to phosphatidylglycerol (PG) were used as the metric of lipid substitution. In cultures of M. aeruginosa NIES-843, the SQDG : PG ratio increased from ~ 0.9 to ~ 3.3 with decreasing P concentration. In P-limited communities, the SQDG : PG ratio increased from ~ 6 to ~ 11 after 48 h in microcosm controls, while P amendments reduced the ratio to ~ 3. In Lake Erie surveys, the SQDG : PG ratio ranged from ~ 0.4 to ~ 7.4 and was negatively correlated (Pearson r = −0.62) with total dissolved P. The SQDG : PG ratio was not correlated with concentrations of chlorophyll a, soluble reactive P, or N : P molar ratios. These results demonstrated that M. aeruginosa and Microcystis-dominated communities remodel lipid profiles in response to P scarcity, providing a potential short-term, time-integrated biomarker of nutrient history and P stress in fresh waters

Metatranscriptomic Analyses of Diel Metabolic Functions During a Microcystis Bloom in Western Lake Erie (United States)

This study examined diel shifts in metabolic functions of spp. during a 48-h Lagrangian survey of a toxin-producing cyanobacterial bloom in western Lake Erie in the aftermath of the 2014 Toledo Water Crisis. Transcripts mapped to the genomes of recently sequenced lower Great Lakes isolates showed distinct patterns of gene expression between samples collected across day (10:00 h, 16:00 h) and night (22:00 h, 04:00 h). Daytime transcripts were enriched in functions related to Photosystem II (e.g., ), nitrogen and phosphate acquisition, cell division (), heat shock response (, ), and uptake of inorganic carbon (, ). Genes transcribed during nighttime included those involved in phycobilisome protein synthesis and Photosystem I core subunits. Hierarchical clustering and principal component analysis (PCA) showed a tightly clustered group of nighttime expressed genes, whereas daytime transcripts were separated from each other over the 48-h duration. Lack of uniform clustering within the daytime transcripts suggested that the partitioning of gene expression in is dependent on both circadian regulation and physicochemical changes within the environment

Sulfolipid profiles of Microcystis aeruginosa and cyanobacterial blooms as an indicator of P availability

While phosphorus (P) scarcity can limit primary productivity in lakes, its oversupply can lead to the formation of cyanobacteria-dominated algal blooms. P availability influences bloom dynamics and can be seasonally limiting, even in eutrophic lakes. Marine phytoplankton alter their lipid profile by increasing sulfolipids when P is limiting. We asked whether Microcystis spp. respond in a similar manner. The ratio of sulfoquinovosyl diaclyglycerol (SQDG) to phosphatidylglycerol (PG) was used to examine lipid remodeling. In batch cultures of M. aeruginosa, the SQDG:PG ratio increased from ~0.9 to ~3.3 with decreasing initial P concentration. In P-limited Lake Erie mesocosms, SQDG:PG increased in controls from ~6 to ~11 after 48 hr, while P-addition decreased the ratio from ~6 to ~3. In non-P-limited mesocosms, the ratio was unchanged after 48 hr and P-addition treatments had no effect. In Lake Erie in situ measurements, SQDG:PG showed an inverse correlation with total dissolved P. There was no correlation with either soluble reactive P or N:P ratio. This study demonstrates that Microcystis remodels its lipid profile in response to P scarcity, providing a potential short-term, time-integrating marker of nutrient history for cyanobacterial populations during fresh water blooms

Metatranscriptomic Analyses of Diel Metabolic Functions During a Microcystis Bloom in Western Lake Erie (United States).

This study examined diel shifts in metabolic functions of Microcystis spp. during a 48-h Lagrangian survey of a toxin-producing cyanobacterial bloom in western Lake Erie in the aftermath of the 2014 Toledo Water Crisis. Transcripts mapped to the genomes of recently sequenced lower Great Lakes Microcystis isolates showed distinct patterns of gene expression between samples collected across day (10:00 h, 16:00 h) and night (22:00 h, 04:00 h). Daytime transcripts were enriched in functions related to Photosystem II (e.g., psbA), nitrogen and phosphate acquisition, cell division (ftsHZ), heat shock response (dnaK, groEL), and uptake of inorganic carbon (rbc, bicA). Genes transcribed during nighttime included those involved in phycobilisome protein synthesis and Photosystem I core subunits. Hierarchical clustering and principal component analysis (PCA) showed a tightly clustered group of nighttime expressed genes, whereas daytime transcripts were separated from each other over the 48-h duration. Lack of uniform clustering within the daytime transcripts suggested that the partitioning of gene expression in Microcystis is dependent on both circadian regulation and physicochemical changes within the environment