## 3 Results and Discussion
### Toxicological Significance  
The luminescent bacteria have been frequently employed for the ecotoxicological screening and assessment of a wide range of potentially deleterious solid, liquid and gaseous substances. The field of toxicity assessment has used the traditional threshold models, linear-no-threshold (LNT) models and hormesis models for study on dose response [36]. Besides the threshold and LNT models, some scholars have proposed the hormesis model to the toxicological evaluation system with an in-depth understanding of hormesis. Hormesis describes a dose-effect relationship characterized by low-dose stimulation and high-dose inhibition. The hormetic effects of heavy metals [37], sulfonamides [38] and ionic liquids [39] on luminescent bacteria have been reported.  
Meanwhile, a few studies have suggested that different species of luminescent bacteria exposed to the same chemical would cause different bioluminescencement responses. For example, 1-ethyl-3-methyl imidazolium tetrafluoroborate (0.01-0.1 mol/L) has a hermetic response to the luminescence of Q67 in the long-term (12 h) toxicity assessment, while a classic concentration response has been observed for _V. fischeri_, other than the hormesis at the same experimental concentration [40]. These results are closely related to the differences in the luminescent regulatory systems of various luminescent bacteria. Therefore, some researchers introduced quorum sensing to toxicity assessment to explain the different luminescence phenomena of luminescent bacteria in response to the same chemical. Based on the molecular docking and quantitative structure-activity relationships, [PERSON] et al. proposed a new hormesis hypothesis for the chronic toxicity evaluation of sulfonamides (SAs) on _P. phosphoreum_ which combined QS with hormesis to explain the dose-dependent and time-dependent characteristics of hormesis [41]. The hypothesis stated that at a low SAs exposure, the SAs have the chance to bind to a receptor protein (LuxR) and might cause the accumulation of LuxR-SA complexes. The autoinducers increase with the cell density and the accumulated autoinducers bind to LuxR, causing bioluminescence. The LuxR-SA complexes might help the bacteria at low density to activate quorum sensing, exhibiting hormesis. At a high SAs exposure, more SAs might bind to dihydroteroate synthase and inhibit folate synthesis, and toxicity was observed when inhibition exceeded stimulation.  
Of particular note, most reports have illustrated the mechanism of the hormesis effect in _V. fischeri_ on the molecular level since the QS regulation of _V. fischeri_ has been studied in detail. As in previous studies, the toxicity mechanism on _P. phosphoreum_ T3 and _V. qinghaiensis_ sp.-Q67 is still unclear on account of lacking conclusions about whether the luminescence process of these two strains is controlled by QS systems. The results of our study showed that the bioluminescence production of T3 and Q67 was controlled by QS, which provided a research basis to reveal the relationship between hormesis and QS in toxicology. Moreover, the crude extract containing autoinducers may trigger different responses to _P. phosphoreum_ T3 and _V. qinghaiensis_ sp.-Q67, implying that luminescent bacteria with different luminescent properties could be applied to various compounds for toxicity assessment.