Seasonal Gene Expression and the Ecophysiological Implications of Toxic Microcystis aeruginosa Blooms in Lake Taihu

Abstract

Harmful cyanobacterial blooms represent an increasing threat to freshwater resources globally. Despite increased research, the physiological basis of how the dominant bloom-forming cyanobacteria, Microcystis spp., proliferate and then maintain high population densities through changing environmental conditions is poorly understood. In this study, we examined the transcriptional profiles of the microbial community in Lake Taihu, China at 9 stations sampled monthly from June to October in 2014. To target Microcystis populations, we collected metatranscriptomic data and mapped reads to the M. aeruginosa NIES 843 genome. Our results revealed significant temporal gene expression patterns, with many genes separating into either early or late bloom clusters. About one-third of genes observed from M. aeruginosa were differentially expressed between these two clusters. Conductivity and nutrient availability appeared to be the environmental factors most strongly associated with these temporal gene expression shifts. Compared with the early bloom season (June and July), genes involved in N and P transport, energy metabolism, translation, and amino acid biosynthesis were down-regulated during the later season (August to October). In parallel, genes involved in regulatory functions as well as transposases and the production of microcystin and extracellular polysaccharides were up-regulated in the later season. Our observation indicates an eco-physiological shift occurs within the Microcystis spp. transcriptome as cells move from the rapid growth of early summer to bloom maintenance in late summer and autumn.

Morphological and Molecular Identification of Microcystin-Producing Cyanobacteria in Nine Shallow Bulgarian Water Bodies

“…The results from conducted molecular-genetic analysis are also in general accordance with data on cyanotoxins, except the lack of MCs over the detection limit of the methods used in Poroy, Vaya, and Mandra [4], and recent discovery of toxigenic mcy sequences in these WBs. The finding of toxigenic sequences in the samples where MCs were not detected by standard methods is not unusual and can be explained with the quite low Microcystis amounts found there by LM, with the temporal character of mcy gene expression patterns (e.g., [41]) and other factors that condition the toxin production, including the growth phase of the populations [42]. The lack of NODs in the checked WBs [4] is also in accordance with the negative PCR signal for NOD-producing genes obtained in this study and the absence of its causative agents, Nodularia species [22], in the phytoplankton samples processed by LM.…”

The “Neglected Viruses” of Taihu: Abundant Transcripts for Viruses Infecting Eukaryotes and Their Potential Role in Phytoplankton Succession

“…Samples were collected in a manner consistent with the separation of bacteria and phytoplankton from dissolved materials: free virus particles generally pass through these filters. Environmental parameters and nutrient data were collected with each sample and have been reported elsewhere (Tang et al, 2018). Total RNA was extracted, quality checked, ribosomally reduced, and sequenced on the Illumina TM HiSeq platform at HudsonAlpha Institute Genomic Services Laboratory (Huntsville, AL, United States) as previously described (Krausfeldt et al, 2017;Stough et al, 2017;Tang et al, 2018).…”

“…Environmental parameters and nutrient data were collected with each sample and have been reported elsewhere (Tang et al, 2018). Total RNA was extracted, quality checked, ribosomally reduced, and sequenced on the Illumina TM HiSeq platform at HudsonAlpha Institute Genomic Services Laboratory (Huntsville, AL, United States) as previously described (Krausfeldt et al, 2017;Stough et al, 2017;Tang et al, 2018). Raw sequence data was retrieved from the HudsonAlpha servers and primarily handled in the CLC Genomics Workbench v. 10.1.1 suite (QIAGEN, Hilden, Germany).…”

“…Freshwater HABs commonly manifest as a summer bloom of cyanobacteria that follows from a winter/spring population of eukaryotic phytoplankton (Ke et al, 2008;Niu et al, 2011;Edgar et al, 2016). HAB research has historically focused on abiotic "bottom-up" controls, such as nutrient or temperature triggers that stimulate cyanobacterial growth (Tang et al, 2018). However, biological success can also arise during suppression of competitors, and there is less known about the decline of the eukaryotic population and factors that constrain these populations as cyanobacterial blooms form.…”

Effects of Microcystin-LR on Metabolic Functions and Structure Succession of Sediment Bacterial Community under Anaerobic Conditions

“…Three different sediment samples (under surface 10-15 cm) were collected from Fudu Bay of Lake Taihu, China, where heavy cyanobacterial blooms occur frequently [33,60]. These samples were packaged in sterile anaerobic bags and transported to the laboratory rapidly at low temperatures to guarantee the activity of the bacterial community.…”