Intracellular mapping of a major metabolite in the filamentous cyanobacterium Moorena bouillonii

The genus Moorena comprises tropical marine cyanobacterial species rich in secondary metabolites with allelopathic properties against competitor reef-constructor organisms, thereby threatening the health of coral reefs. Nevertheless, few studies have addressed the cellular localization and extracellular secretion of these crucial chemicals involved in chemically mediated ecological interactions. We combined spectroscopy, microscopy, chromatography, and chemical analyses to localize the major secondary metabolite in Moorena bouillonii. Confocal Microscopy revealed a bluish emission pattern observed in the mucilaginous sheath around the cyanobacterial trichome - inside the vesicles, between the cells, and in the necridia. A crude extract of M. bouillonii was fractionated by HPLC and the purified fraction analyzed by Raman spectroscopy presented bands indicative of a potential pyridine ring as major peaks, which may correspond to nitrogen-containing phenolic compounds or a pyridine alkaloid. Raman map revealed the highest concentration of the major compound in the intracellular region (above the thylakoid membranes), gradually decreasing outward toward the mucilaginous sheath. The location of the major compound within M. bouillonii cells suggests a dynamic chemical defense system in which the compound is biosynthesized near the thylakoid membranes and transported to the mucilaginous sheath, in a process analogous to those observed in marine macroalgae with known defensive ecological roles. The use of Raman, FT-IR, and Confocal Microscopy analysis provides comprehensive chemical and morphological insights that are often crucial for research focused on environmental monitoring.