Molluscs vs. bacteria: New finding on marine natural products biosynthesis

Experts Conxita Àvila and Anna Domènech-Coll, from the Department of Animal Biology at the Faculty of Biology of the UB, affiliated centre with the campus of international excellence BKC, collaborated in the article, which is also signed by Guido Cimino, Angelo Fontana and Adele Cutignano (Institute of Biomolecular Chemistry, Naples), and other international experts.

Chemical strategies to survive on seabed

Opisthobranchs are a group of marine invertebrates that constitute a source of marine bioactive products. Scaphander lignarius is a benthic mollusc that belongs to the order Cephalaspidea -- the most primitive opisthobranchs -- and lives on moody sand bottoms. It is common to find this opisthobranch gastropod, which eats forams, polychaetes and small marine bivalves, in fishing trawlers' activity. In marine ecophysiology studies, it is a model to study chemical defence strategies -- with secondary metabolites -- to compensate the loss or reduction of its mechanical protection (shell).

Professor Conxita Àvila, who also coordinates Actiquim-II, a research project to study natural marine products in Antarctic ecosystems and determine their potential for use in pharmacological applications, points out that "lignarenones are secondary metabolites which work as potential alarm pheromones in natural ecosystems." "Secondary metabolites -- she adds -- are an extremely diverse group of natural compounds synthesized by organisms and molecules involved in ecological interactions among organisms and the environment."

Lignarenones synthesis: a link between bacteria and opisthobranchs

Organisms show a great variety of physiological adaptations to their habitat. The article published on the journal ChemBioChem reveals that this opisthobranch is able to synthetize lignarenones, a biological function that was exclusively associated to prokaryotes until now. Lignarenone biosynthesis revealed a polyketide pathway primed by benzoic acid in the cytoplasm of specialised eukaryotic cells. Besides identifying this biosynthesis route in Scaphander lignarius, the article also shows that polyketide biosynthesis is associated with specialised molluscan cells, Blochmann's glands, which are distributed in biosynthetic tissue localised in the vulnerable mantle of the mollusc.

The research extends scientific knowledge on the role that marine invertebrates play in natural products biosynthesis. "This is the first direct evidence -- highlights Conxita Àvila -- that confirms the biological ability of this group of marine invertebrates to synthetize this type of natural products. Therefore, this lineage of gastropods is genetically able to produce this type of metabolites, which are useful for their survival." According to the expert, "this ability is not derived from a symbiotic relationship with bacteria; the biosynthetic process suggests genetic convergence across different kingdoms."

Besides synthetizing lignarenones, Scaphander lignarius shares other ability with prokaryotes. The research also reports the first verification of a phenylalanine ammonia lyase (PAL) activity -- an enzyme that takes part in the synthesis of those metabolites which play a major role in chemical defence -- in a biological group different from bacteria.

Searching for new marine-based drugs

Marine ecosystems are a great natural source of bioactive substances with potential uses in pharmaceutical sectors (antitumor agents, etc.). Nowadays, we know more than 20,000 substances derived from marine macro- and micro-organisms, but potential properties of marine natural products continue to be ignored. According to Professor Conxita Àvila, expert on marine invertebrates' chemical ecology, "besides the efforts made by research groups, the collaboration of pharmaceutical companies is necessary to find new marine biomolecules which provide solutions in the field of biomedicine."