Sunlight can greatly enhance the toxicity of polycyclic aromatic hydrocarbons (PAHs). Photosensitization reactions (e.g., generation of singlet-state oxygen) and photomodification reactions (e.g., photooxidation of PAHs to more toxic species) are both pathways of photoinduced toxicity of PAHs. Previously, a quantitative structure-activity relationship (QSAR) was developed for PAHs showing that a photosensitization factor (PSF) and photomodification factor (PMF) can be additively combined to describe photoinduced toxicity. That QSAR model was developed for the photoinduced toxicity of 16 PAHs to the higher plant Lemna gibba. The objective of this study was to apply the QSAR model developed for L. gibba to another organism. The organism chosen was the luminescent marine bacteria Vibriofischeri. Toxicity data used for the QSAR model were inhibition of luminescence and inhibition of growth of V. fischeri. Both short-term (15 min) and long-term (18 h) assays of toxicity were used. Light did not impact on PAH toxicity in the short-term assay, and thus the QSAR model did not correlate well with these data. Conversely, light greatly enhanced toxicity when the long-term assay was employed. The PMFs for the PAHs from the L. gibba QSAR showed a moderate correlation to bacterial toxicity in the long-term assay, whereas the PSFs showed only a weak correlation to toxicity. As was the case for L gibba, summing the PMF and the PSF resulted in a strong correlation to toxicity that had predictive value. Thus, a QSAR model derived for plants accurately described the toxicity of PAHs to a bacterial species. This indicates that the bipartite mechanism of PAH-photoinduced toxicity may be applicable to other organisms.