Friends or foes? Allelopathic effects within a 3-microalgal consortium.

This study investigates allelopathic interactions within a consortium of three green microalgae, Tetradesmus obliquus, Chlamydomonas reinhardtii, and Auxenochlorella protothecoides, to elucidate how intra- and interspecific chemical signals modulate growth dynamics and biomass composition. Monocultures and mixed-species cultures were exposed to spent media, while key growth parameters were monitored. The chemical profile of the media was assessed via Total X-ray Fluorescence (TXRF) and Fourier-transform infrared spectroscopy (FTIR), whereas Dynamic Light Scattering (DLS) was employed to detect extracellular vesicles (algosomes). Exposure to spent media elicited species-specific responses that were consistently non-deleterious; specifically, C. reinhardtii and A. protothecoides exhibited increased growth rates, while T. obliquus showed enhanced cell density. Furthermore, allelopathic signals regulated morphological plasticity in T. obliquus, with interspecific cues inducing a marked reduction in colony size. FTIR analysis of the algal biomass revealed a metabolic reallocation favouring protein and lipid accumulation over carbohydrate reserves. Finally, DLS confirmed the secretion of extracellular vesicles, suggesting their potential involvement in this chemical communication. These findings demonstrate that positive allelopathic signals can enhance algal productivity and modify biomass quality, offering valuable perspectives for optimizing biotechnological cultivation.