## 3 Results and Discussion
### Differences in the Stimulations of Crude Culture Extract between T3 and Q67  
QS as a cell-density-dependent phenomenon allowed bacteria to coordinate their physiology via the release of autoinducers (AIs). Once AIs were produced by the corresponding synthases, they were sent out and perceived by the community microbes that enumerate their population density. After reaching threshold concentrations, changes in microbial gene expression are induced, triggering population cooperation. The primary AIs synthesized by gram-negative bacteria are AHL molecules that consist of a homoserine lactone ring (HSL) with an acyl chain. The acyl-chain length generally varies from C4 to C18 and can be modified by a 3-oxo substituent, a 3-hydroxy substituent, a terminal methyl branch, or varying degrees of unsaturation. In wastewater treatment, studies have borne out claims that exogenous addition of AHLs or AHL-producing bacteria could enhance sludge performance, such as biofilm and maturation [25], microbial aggregation and stabilization [26] and granule formation [27]. According to the report of [PERSON] et al. [26], exogenous AHLs (3-oxo-C\({}_{8}\)-HSL, C\({}_{8}\)-HSL, C\({}_{6}\)-HSL and C\({}_{4}\)-HSL) enhanced the degrading ability of oligotrophic anaerobic granular sludge to remove residual refractory substances and optimize the microbial community structure by increasing the abundances of favourable bacterial groups. Concerning luminescent bacteria, the luminescent intensity would increase with the autoinducers in a certain concentration range. A case reported by [PERSON] and [PERSON] supported the statement that the luminescence intensity of _V. fischeri_ would increase when the amount of adding autoinducer was 10 to 100 nM [28]. [PERSON] and [PERSON] also found that the bioluminescence of _V. fischeri_ in bacterial cultures with AHLs (3-oxo-C6-HSL, 1 uM) commenced earlier and was approximately 100% greater after 8.5 h compared with the untreated controls [29]. Therefore, the crude culture extracts containing potential AIs from the two bacterial supernatants were prepared and introduced into the culture media at different concentrations (175 mg/L, 350 mg/L, 700 mg/L and 1750 mg/L) to investigate the effect of potential Als on the growth and the light intensity of the T3 and Q67 (Figure 3). For Q67, the stimulus effects of the crude extract were not noteworthy in test groups during 0.25-8 h (Figure 3b). However, the light intensity dramatically increased in all test groups after 8 h compared with control groups (without crude culture extract addition). Furthermore, the luminescence intensity was enhanced with the increasing concentration of added crude extract after 8 h. It is worth mentioning that there were no significant differences in cell density between the control and the test group throughout the experiment. When the added crude extract was up to 1750 mg/L, the cell density (OD) of the control and test group at 8 h reached 0.80, while the luminescence intensity of the test group increased by 100-fold (Figure 3b). This result indicated that the potential autoinducers in crude extract could work with the receptor protein to turn on the expression of the light-emitting gene for Q67. The test groups of T3 did not show an obvious light intensity and cell density change after adding extra crude extracts with lower concentrations of 175 and 350 mg/L (Figure 3a). When adding the crude extracts at 700 and 1750 mg/L, the light intensity decreased with the increase of extract dosage at the exponential and the early stationary growth phase.