Abstract
While most studies on allelopathic interactions among autotrophic microorganisms focus on free-living aquatic species, little is known about microalgal biofilms, where chemical communication is enhanced by spatial proximity. A co-culture protocol using a disc diffusion method was developed to assess the inhibitory potential of the marine diatom Cylindrotheca closterium growing in non-axenic conditions, against different targeted algal strains. The biofilm exhibited an inhibitory effect on the individual growth of two algal strains, Nannochloropsis oculata and Tetraselmis striata, but did not affect the microalga Porphyridium purpureum. The findings highlight the potential of such allelopathic interactions, making C. closterium a candidate for contamination-resistant algal biofilm technologies. Further research is needed to identify the inhibitory compounds and their microbial producers within the growing biofilm.