Salt Shock Responses of Microcystis Revealed through Physiological, Transcript, and Metabolomic Analyses

Abstract

The transfer of Microcystis aeruginosa from freshwater to estuaries has been described worldwide and salinity is reported as the main factor controlling the expansion of M. aeruginosa to coastal environments. Analyzing the expression levels of targeted genes and employing both targeted and non-targeted metabolomic approaches, this study investigated the effect of a sudden salt increase on the physiological and metabolic responses of two toxic M. aeruginosa strains separately isolated from fresh and brackish waters, respectively, PCC 7820 and 7806. Supported by differences in gene expressions and metabolic profiles, salt tolerance was found to be strain specific. An increase in salinity decreased the growth of M. aeruginosa with a lesser impact on the brackish strain. The production of intracellular microcystin variants in response to salt stress correlated well to the growth rate for both strains. Furthermore, the release of microcystins into the surrounding medium only occurred at the highest salinity treatment when cell lysis occurred. This study suggests that the physiological responses of M. aeruginosa involve the accumulation of common metabolites but that the intraspecific salt tolerance is based on the accumulation of specific metabolites. While one of these was determined to be sucrose, many others remain to be identified. Taken together, these results provide evidence that M. aeruginosa is relatively salt tolerant in the mesohaline zone and microcystin (MC) release only occurs when the capacity of the cells to deal with salt increase is exceeded.

Physiological changes induced by sodium chloride stress in Aphanizomenon gracile, Cylindrospermopsis raciborskii and Dolichospermum sp.

“…Chen et al, 2015;Gong et al, 2008;Lu and Vonshak, 2002;Ross et al, 2019). In accordance with the present study, when salinity concentration was sufficiently high to induce a stress, a decreased Fv/Fm was observed in Spirulina platensis (Gong et al, 2008;Lu et al, 1999) and M. aeruginosa Aulnois et al, 2020;Ross et al, 2019). In line with the A. gracile and C.…”

“…This is also in line with the sucrose accumulation observed in a particularly salt-tolerant M. aeruginosa strain, isolated from brackish waters (Georges des Aulnois et al, 2019). The protective role of sucrose during salt stress was further confirmed in the same M. aeruginosa strain by the over-expression of genes involved in its synthesis in response to salinity increase (Georges des Aulnois et al, 2020).…”

“…Aguilera-Belmonte et al, 2013 and references therein) or salt effects on other cyanotoxins such as microcystins (e.g. Aulnois et al, 2020;Georges des Aulnois et al, 2019;Melero-Jiménez et al, 2020 and references therein). Additionally, some of the STXs-cyanobacteria species remain poorly studied.…”

Effect of a short-term salinity stress on the growth, biovolume, toxins, osmolytes and metabolite profiles on three strains of the Dinophysis acuminata-complex (Dinophysis cf. sacculus)

“…Three successive filtering steps using in-house scripts on R were applied, as in Georges des Aulnois et al (2020). Pre-processing of +MS and -MS data matrices led to 8458 and 2651 variables respectively, and 540 and 203 variables remained after the filtrations.…”

“…Other molecules acting like osmolytes have been described (Rhodes et al, 2002) and characterized after salinity changes by liquid chromatography coupled to high resolution mass spectrometry (e.g. sucrose; Georges des Aulnois et al 2020).…”