Periodic Reporting for period 2 - CHEMICROS (CHEmically-mediated MICRobial Interactions maintained by the toxic dinoflagellate OStreopsis cf. ovata)
Período documentado: 2021-08-01 hasta 2022-07-31
Proliferation of harmful marine microalgae are increasing worlwide due to eutrophication and temperature rise of surface waters. These Harmful Algal Blooms (HABs) cause damages to living organisms through high biomass accumulation or through production of biotoxins in the algal cells. Extensive repercussions of HABs on human health, aquatic species, commercial fisheries, aquaculture and tourism are yearly recorded worldwide and related economic losses can be measured in millions of dollars. Given their impacts, the increasing occurrence of HABs worldwide constitutes a major ecological issue for the coming decades. HABs species are highly suspected to rely on chemical interactions with the microbial community to support their proliferation. A better understanding of these interactions could help improving management strategies for HABs events, including mitigation and forecasting.
In this context, the project CHEMICROS aimed to investigate the microbial control on the toxicity of blooms of the benthic dinoflagellate Ostreopsis cf. ovata. This species is now well settled in the Mediterranean Sea and frequently leads to respiratory distress or dermatitis in Humans. Three main scientific objectives were investigated: (1) influence of the chemical interactions between the bacteria and Ostreopsis on the algal growth and the phycotoxins’ biosynthesis, (2) evaluation of the transformation of waterborne phycotoxins exposed to bacteria and solar radiation, as well as the assessment of the transfer of the phycotoxins to the sea spray aerosols, and (3) characterization of an algicide produced by a co-occurring benthic diatom as a promising bio-agent for bloom mitigation.
To meet the stated objectives, a combination of laboratory work with cultures of microalgae and field campaigns was used. State-of-the-art analytical tools such as High Resolution Mass Spectrometry (HRMS) allowed the measurement of low-levels of phycotoxins in complex matrices. Un-targeted metabolomics approaches and molecular networking allowed the identification of phycotoxins by-products or chemical mediators of the bacteria-microalgae interaction. Approaches in natural products chemistry were used to isolate and characterize the algicidal compound.
This action allowed gaining more fundamental knowledge on the chemical interactions maintained by Ostreopsis and its bacterial community, as well as the control by bacteria on the phycotoxins’ biosynthesis. Also, the insights gained on the instability of the phycotoxins produced by O. cf. ovata and the mechanisms driving their transfer to the sea spray aerosols are of significant importance to unravel the toxic effects on human health associated with these blooms. Lastly, the identification of a bio-agent that inhibits temporarily the cell’s proliferation may pave the way for innovative solutions for the bio-mitigation of these toxic blooms.
In this context, the project CHEMICROS aimed to investigate the microbial control on the toxicity of blooms of the benthic dinoflagellate Ostreopsis cf. ovata. This species is now well settled in the Mediterranean Sea and frequently leads to respiratory distress or dermatitis in Humans. Three main scientific objectives were investigated: (1) influence of the chemical interactions between the bacteria and Ostreopsis on the algal growth and the phycotoxins’ biosynthesis, (2) evaluation of the transformation of waterborne phycotoxins exposed to bacteria and solar radiation, as well as the assessment of the transfer of the phycotoxins to the sea spray aerosols, and (3) characterization of an algicide produced by a co-occurring benthic diatom as a promising bio-agent for bloom mitigation.
To meet the stated objectives, a combination of laboratory work with cultures of microalgae and field campaigns was used. State-of-the-art analytical tools such as High Resolution Mass Spectrometry (HRMS) allowed the measurement of low-levels of phycotoxins in complex matrices. Un-targeted metabolomics approaches and molecular networking allowed the identification of phycotoxins by-products or chemical mediators of the bacteria-microalgae interaction. Approaches in natural products chemistry were used to isolate and characterize the algicidal compound.
This action allowed gaining more fundamental knowledge on the chemical interactions maintained by Ostreopsis and its bacterial community, as well as the control by bacteria on the phycotoxins’ biosynthesis. Also, the insights gained on the instability of the phycotoxins produced by O. cf. ovata and the mechanisms driving their transfer to the sea spray aerosols are of significant importance to unravel the toxic effects on human health associated with these blooms. Lastly, the identification of a bio-agent that inhibits temporarily the cell’s proliferation may pave the way for innovative solutions for the bio-mitigation of these toxic blooms.
Molecules produced and released by the bacterial community associated with the toxic dinoflagellate Ostreopsis cf. ovata stimulate the proliferation of algal cells. Therefore, bacteria living in commensal association with the dinoflagellate applies a chemical control on the microalgal growth but does not influence the phycotoxins’ biosynthesis. The chemicals mediating this interaction are unknown compounds, some of which containing halogenated atoms. Bacteria were also shown to alter the chemical structure of the phycotoxins once they are released in seawater by the algal cells. The phycotoxins' half-lives are very short under bacterial activity (< 10 hours) and to a lesser extent under solar radiation (> 36-62 hours according to the toxin). This reduced stability of waterborne phycotoxins explains why undetectable concentrations in the water column or the sea surface microlayer were measured in the field or in a controlled system mimicking a real bloom. The controlled experiment confirmed the presence of phycotoxins in the aerosols in an enclosed system, indicating that without wind dispersion, Ostreopsis’ phycotoxins can be detected to the sea spray aerosols. However, the undetectable concentrations of the waterborne phycotoxins suggest an unusual mechanism for this transfer: rather than waterborne toxins aerosolization, the mucus or cell debris would rather be the vector for this transfer. A field campaign confirmed the presence of several of the known phycotoxins in the aerosols produced during a natural bloom of O. cf. ovata. However, very low levels, under the detection limit of the instrument (HRMS), were detected most sampling days, raising the question about the relationship between phycotoxins in sea spray aerosols and respiratory distress in Humans. To unravel this question, future work should involve assessment of the inflammatory potential of natural aerosols emitted during a bloom of O. cf. ovata. Bio-mitigation of HABs is often suggested as a sustainable solution for the control of toxic proliferation. In this context, the characterization of an algicidal compound produced by a co-occurring benthic diatom Licmophora paradoxa led to the identification of a fatty acid containing 13 carbon atoms. This simple molecule is able to induce dormant forms (encystment) in the dinoflagellate O. cf. ovata. A positive dose-effect was observed when O. cf. ovata was exposed to the algicide. In addition, the discovery of two new families of toxins produced by O. cf. ovata, that were named liguriatoxins and rivieratoxins, suggests that the chemical diversity in dinoflagellates is far from being thoroughly unraveled.
The results are mainly being disseminated within the scientific community through several peer-reviewed publications as well as through national and international conferences. However, the knowledge acquired on the unstable character of the waterborne phycotoxins and their transfer to the aerosols are of high importance to assess the toxicity of the blooms. This knowledge is currently used within a national group of experts working on the Ostreopsis hazards in the French Basque area. The output of this working group will be a review of the existing knowledge as well as recommendations to local marine stakeholders dealing with blooms of O. cf. ovata. Additionally, the newly described toxins could be added to the phycotoxins monitoring effort performed by national institutes of the whole Mediterranean basin.
The results are mainly being disseminated within the scientific community through several peer-reviewed publications as well as through national and international conferences. However, the knowledge acquired on the unstable character of the waterborne phycotoxins and their transfer to the aerosols are of high importance to assess the toxicity of the blooms. This knowledge is currently used within a national group of experts working on the Ostreopsis hazards in the French Basque area. The output of this working group will be a review of the existing knowledge as well as recommendations to local marine stakeholders dealing with blooms of O. cf. ovata. Additionally, the newly described toxins could be added to the phycotoxins monitoring effort performed by national institutes of the whole Mediterranean basin.
The CHEMICROS project significantly improved our knowledge of the nature and the fate of the phycotoxins associated with blooms of O. cf. ovata. The new toxins discovered should be added to the list of monitored phycotoxins by the relevant agencies. The characterized algicide could be further considered as a bio-agent for the mitigation of blooms of O. cf. ovata in order to avoid extensive wildlife death events and health impacts on coastal populations associated with these blooms. Lastly, a new route for the aerosolization of the phycotoxins is proposed based on the results obtained on their instability in seawater and their concentration in sea spray aerosols. These findings should help local stakeholders to implement thresholds for the algal cell abundance in seawater as a proxy for phycotoxins in the aerosols. The methods and knowledge developed during this project may also be used for other dinoflagellate species causing similar symptoms on Humans.