Harmful algal blooms (HABs) pose serious health and economic problems due to biotoxins produced by algae species. A biosensing method employing luminous bacteria was used to detect and characterize the response generated when encountering four critical harmful algae, Karlodinium micrum, Pfiesteria piscicida, Chattonella marina, and Prorocentrum minimum. This sensing system includes six Escherichia coli strains containing different stress-responsive promoters fused to the Photohabdus luminescens luxCDABE reporter. At the concentration of approximatly 6,000 cells/ml, these algal species induced stress responses of the biosensing strains higher than did the control, a non-toxic dinoflagellate Akashiwo sanguinea. The stress responses induced by harmful species showed unique patterns for each of the algae investigated, suggesting that characteristic fingerprints could be generated based on such stress responses. Moreover, dose dependency was observed between the bioluminescence from the sensing strains and the level of algae concentrations, indicating possible quantification of harmful algal species using specific stress response.