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The impact of cation concentration on Microcystis (cyanobacteria) scum formation.

ABSTRACT: Cyanobacterial scums at the surface of the lakes are potentially harmful phenomena with increasing occurrence in the last decades, and the causes that lead to their formation are still an unresolved issue. In order to better understand what triggers the scums, we investigated the effect of several Mg2+ and Ca2+ ion concentrations in promoting them in eight Microcystis aeruginosa strains. The possibility to prevent scum formation by using the ion chelator EDTA was also explored. We found that in some strains the cell aggregation takes place under lower ion source concentrations (20?mM MgSO4 or CaCl2), while in others this phenomenon does not occur even at 60?mM concentration. The scum formation correlated to the amount of extracellular polymeric substances (between 234 and 351?µg/cell). EDTA failed to prevent the scum formation in most strains, and in turn it caused cell lysis followed by the release of cellular content into the culture medium. We emphasize the relevance of these results for cyanobacterial scum formation in the environment and we also suggest that controlling the salinity of the medium (by manipulating the ion concentration) is a potentially efficient method for biomass harvesting in large ponds/tanks.

SUBMITTER: Druga B

PROVIDER: S-EPMC6395708 | biostudies-literature | 2019 Feb

REPOSITORIES: biostudies-literature

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The impact of cation concentration on Microcystis (cyanobacteria) scum formation.

Drugă Bogdan B Buda Doriana-Mădălina DM Szekeres Edina E Chiş Ciprian C Chiş Iuliana I Sicora Cosmin C

Scientific reports 20190228 1

Cyanobacterial scums at the surface of the lakes are potentially harmful phenomena with increasing occurrence in the last decades, and the causes that lead to their formation are still an unresolved issue. In order to better understand what triggers the scums, we investigated the effect of several Mg<sup>2+</sup> and Ca<sup>2+</sup> ion concentrations in promoting them in eight Microcystis aeruginosa strains. The possibility to prevent scum formation by using the ion chelator EDTA was also explo ...[more]

PMID: 30816221

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Project description:Cyanobacteria of the genus Microcystis are known to produce secondary metabolites of large structural diversity by nonribosomal peptide synthetase (NRPS) pathways. For a number of such compounds, halogenated congeners have been reported along with nonhalogenated ones. In the present study, chlorinated cyanopeptolin- and/or aeruginosin-type peptides were detected by mass spectrometry in 17 out of 28 axenic strains of Microcystis. In these strains, a halogenase gene was identified between 2 genes coding for NRPS modules in respective gene clusters, whereas it was consistently absent when the strains produced only nonchlorinated corresponding congeners. Nucleotide sequences were obtained for 12 complete halogenase genes and 14 intermodule regions of gene clusters lacking a halogenase gene or containing only fragments of it. When a halogenase gene was found absent, a specific, identical excision pattern was observed for both synthetase gene clusters in most strains. A phylogenetic analysis including other bacterial halogenases showed that the NRPS-related halogenases of Microcystis form a monophyletic group divided into 2 subgroups, corresponding to either the cyanopeptolin or the aeruginosin peptide synthetases. The distribution of these peptide synthetase gene clusters, among the tested Microcystis strains, was found in relative agreement with their phylogeny reconstructed from 16S-23S rDNA intergenic spacer sequences, whereas the distribution of the associated halogenase genes appears to be sporadic. The presented data suggest that in cyanobacteria these prevalent halogenase genes originated from an ancient horizontal gene transfer followed by duplication in the cyanobacterial lineage. We propose an evolutionary scenario implying repeated gene losses to explain the distribution of halogenase genes in 2 NRPS gene clusters that subsequently defines the seemingly erratic production of halogenated and nonhalogenated aeruginosins and cyanopeptolins among Microcystis strains.

Project description:Toxic cyanobacterial blooms are a major contaminant in inland aquatic ecosystems. Furthermore, toxic blooms are carried downstream by rivers and waterways to estuarine and coastal ecosystems. Concerning marine and estuarine animal species, very little is known about how these species are affected by the exposure to freshwater cyanobacteria and cyanotoxins. So far, most of the knowledge has been gathered from freshwater bivalve molluscs. This work aimed to infer the sensitivity of the marine mussel Mytilus galloprovincialis to single as well as mixed toxic cyanobacterial cultures and the underlying molecular responses mediated by toxic cyanobacteria. For this purpose, a mussel exposure experiment was outlined with two toxic cyanobacteria species, Microcystis aeruginosa and Chrysosporum ovalisporum at 1 × 105 cells/mL, resembling a natural cyanobacteria bloom. The estimated amount of toxins produced by M. aeruginosa and C. ovalisporum were respectively 0.023 pg/cell of microcystin-LR (MC-LR) and 7.854 pg/cell of cylindrospermopsin (CYN). After 15 days of exposure to single and mixed cyanobacteria, a depuration phase followed, during which mussels were fed only non-toxic microalga Parachlorella kessleri. The results showed that the marine mussel is able to filter toxic cyanobacteria at a rate equal or higher than the non-toxic microalga P. kessleri. Filtration rates observed after 15 days of feeding toxic microalgae were 1773.04 mL/ind.h (for M. aeruginosa), 2151.83 mL/ind.h (for C. ovalisporum), 1673.29 mL/ind.h (for the mixture of the 2 cyanobacteria) and 2539.25 mL/ind.h (for the non-toxic P. kessleri). Filtering toxic microalgae in combination resulted in the accumulation of 14.17 ng/g dw MC-LR and 92.08 ng/g dw CYN. Other physiological and biochemical endpoints (dry weight, byssus production, total protein and glycogen) measured in this work did not change significantly in the groups exposed to toxic cyanobacteria with regard to control group, suggesting that mussels were not affected with the toxic microalgae. Nevertheless, proteomics revealed changes in metabolism of mussels related to diet, specially evident in those fed on combined cyanobacteria. Changes in metabolic pathways related with protein folding and stabilization, cytoskeleton structure, and gene transcription/translation were observed after exposure and feeding toxic cyanobacteria. These changes occur in vital metabolic processes and may contribute to protect mussels from toxic effects of the toxins MC-LR and CYN.

Dataset Information

The impact of cation concentration on Microcystis (cyanobacteria) scum formation.

Publications

The impact of cation concentration on Microcystis (cyanobacteria) scum formation.

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