Thèse de Madame Shareen A ABDUL MALIK

PhD defence de Mrs. Shareen A ABDUL MALIKPhD defence de Mrs. Shareen A ABDUL MALIK in Laboratoire de Biotechnologie et Chimie Marines

Shareen A ABDUL MALIK's thesis defence, realized within the framework of the ECOS Nord project with Mexico, has been defended on July 7th in Vannes at the LBCM.


Defence on surface of Rhodophyta Halymenia floresii: metabolomic profile and interactions with its surface-associated bacteria.


The surface of Halymenia floresii, a Mexican Rhodophyta, was observed to be remarkably free of epiphytes under Integrated MultiTrophic Aquaculture (IMTA) conditions. This suggests the presence of allelopathic active compounds released by this macroalgae. The aim of this work was to explore the defence mechanisms developed by H. floresii against surface epibiosis, to detect and identify the secondary metabolites produced at the surface of the algae, and to study its relation with surface associated bacteria. For the first time, we isolated the epibacterial community of H. floresii cultivated under controlled conditions (IMTA) and uncontrolled ones (beach-cast material collected in the area). The isolated epibacteria were screened in vitro to analyse Quorum Sensing (QS) signals, and others H. floresii surface extracts were assayed for any QS interference with them. We differentiated the epibacteria significant pathogens from the nonpathogens ones by their ability to induce bleaching, a well-known algal disease. Vibrio owensii was
identified as an opportunistic pathogen inducing bleaching in H. floresii which was also associated to the presence of its C4-HSL QS signal.


The surface and whole cell metabolites extracts from H. floresii specimens cultivated under controlled conditions were analysed by means of LC/MS. An untargeted metabolomic analysis of H. floresii was performed to provide a global metabolic profile as a first database. We identified ‘41’ active metabolites in H. floresii, among which halogenated compounds, furanones and various inhibitors were overrepresented. Interestingly, the first two classes are well known potent QS interfering compounds. The relatively higher occurrences of allelopathic metabolites at the surface of H. floresii strongly supports the hypothesis that they must be involved in the host protection. Further investigations are needed to explore the secondary metabolites of H. floresii et their role in the seaweed.

Key words: Halymenia floresii, antibiofilm, antifouling, metabolomics, surface-associated bacteria, quorum sensing, defence molecules

Jury members


  • Dr Gérald CULIOLI, Maître de Conférences HDR, Université de TOULON
  • Dr Leila TIRICHINE DELACOUR, Directrice de Recherche CNRS Université de NANTES


  • Pr Claire GACHON, Muséum National d’Histoire Naturelle Paris
  • Pr Gwenaëlle LE BLAY, Université Bretagne Occidentale


The work was supervised by Nathalie BOURGOUGNON, Gilles BEDOUX and Daniel ROBLEDO.


Due to the health crisis related to COVID-19, the presentation was not accessible to the public but was simultaneously retransmitted on youtube:



This thesis led to


A Abdul Malik S., Bedoux G., Garcia Maldonado J. Q., Freile-Pelegrín Y., Robledo D., & Bourgougnon N. (2020) Chapter 10. Defense on surface: macroalgae and their surface-associated microbiome. Seaweeds Around the World: State of Art and Perspectives. Advances Botanical research, Volume 95.  ISBN: 978-0-08-102710-3.


A Abdul Malik S., Bedoux G., Robledo D., Garcia Maldonado J. Q., Freile-Pelegrín Y., & Bourgougnon N. (2020) Chemical defense against microfouling by allelopathic active metabolites of Halymenia floresii (Rhodophyta). Journal of Applied Phycology 10.1007/s10811-020-02094-4.


A Abdul Malik S., Bazire A., Gamboa A., Bedoux G., Robledo D., Garcia Maldonado J. Q., & Bourgougnon N. (2020) Quorum Sensing screening in the surface-associated bacteria of the Mexican red alga, Halymenia floresii. Microbiology, submitted


International Conferences

A Abdul Malik S., Gamboa A., Bedoux G., Garcia Maldonado J. Q., Bourgougnon N., & Robledo D. Composition, symbiosis and pathogenesis, an equilateral relationship of the surface-associated microbiome of the cultivated Mexican Rhodophyta, Halymenia floresii, 67th Annual Meeting of The British Phycological Society (07 January – 10 January, 2019) Scottish Association of Marine Sciences, Oban, Scotland.


A Abdul Malik S., Bedoux G., Robledo D., Garcia Maldonado J. Q., Freile-Pelegrín Y., & Bourgougnon N. Chemical defence by allelopathic active metabolites on the surface of cultivated Mexican Rhodophyta Halymenia floresii against biofouling, 23rd International Seaweed Symposium (28 April – 03 May, 2019), International Seaweed Association, Jeju, Korea. First Price for Conference.


Oral National

A Abdul Malik S., Caamal-Fuentes E., Ávila-Velázquez V., Bedoux G., Bourgougnon N., Robledo D. Involvement of allelopathic active metabolites on the surface of the cultivated Halymenia floresii in the biofouling phenomenon, Société Phycologique de France, Paris.