## 4 QS Inhibition in the Context of Fish Preservation
### QS Inhibiting Agents  
The agents that target pseudomonads AIs include mainly lactonases, acylases (also known as amidases or aminohydrolases), and oxidoreductasenes. Enzymes can lead to one of the following effects: (i) AI-degradation for fine-tuning the endogenous QS system, (ii) AI-degradation for modulating the QS system, and (iii) AI-degradation as a mechanism to use AIs for nutrient sources. Inactivation of AI synthases and modification/degradation of AIs affect the QS system of pseudomonads [57]. Among lactone-degrading enzymes, metallo-\(\beta\)-lactamase-like lactonases (MLL) and phosphotriesterase-like lactonases (PLL) are the main studied families [57; 58]. They share a common catalytic mechanism and their differences in AHL substrate preference lie in how the acyl chain can be accommodated into the catalytic site [59]. PLL favors long aliphatic lactones as substrates, whereas MLL exhibits board AHL specificity. The work of [PERSON] et al. [60] confirms that levels of C4-HSL and 3-oxo-C12-HSL and low expression of _las_ and _rhl_ genes in _P. aeruginosa_ were due to PLL and MLL activity. Acylases hydrolase the amide bond between the acyl chain and the homoserine lactone ring [57]. Four AHL-acylases are present in _P. aeruginosa_: namely _pvdQ_, _quiP_, _lacB_,and PA1893 [61]. When _P. aeruginosa_ is grown in a rich medium, the constitutive expression of these acylases shows a decreased level of 3-oxo-C12-HSL. Vice versa, disruption of the acylase genes resulted in a higher concentration of AIs. In addition, a _\(\Delta\)lacB_ single mutant and a _\(\Delta\)pvdQ_, _AhacB_, and _\(\Delta\)quiP_ triple mutant secrete more efficiently 3-oxo-C12-HSL in comparison to _\(\Delta\)pvdQ_, _\(\Delta\)quiP_ double mutant that produced AHLs in the same level as wild-type pseudomonads. This observation indicates that HacB might be working as the main acylase in controlling 3-oxo-C12-HSL accumulation in pseudomonads [62]. Oxidoreductase modify AIs by oxidizing or reducing the acyl chain at the third or distal carbon without degrading the AHLs [58]. Such modification may also affect the specificity and recognition of the AIs, thus disturbing the activation of the QS-mediated genes [63]. BiPiB09 oxidoreductaseate derived from a metagenomics library was found to be capable of inactivating 3-oxo-C12-HSL in _P. aeruginosa_[64]. Its expression in pseudomonads resulted in significantly reduced QS-controlled bacteria phenotypes. QS inhibiting agents also target QS receptors that inactivate the receptor or compete with the receptor. Tepenes and flavonoids of plant essential oils (EOs), as well as halogenated furanones derived from algae, can bind to QS receptors [21]. Examples of natural QS inhibiting agents against _Pseudomonas_ spp. are presented in Table 2. For instance, a plant flavonoid naringenin competes with the 3-oxo-C12-HSL by binding to the LasR receptor leading to inhibition of QS-regulated virulence factors in _Pseudomonas_ spp. [65]. Methyl eugenol and \(\beta\)-phellandrene of tarragon EO [39] and quercetin [54] show similar anti-QS activities [66]. Methyl eugenol, \(\beta\)-phellandrene, and quercetin were successfully docked into the LasR of pseudomonads [54,66]. High docking score values of the examined agents-LasR receptor were due to the range of H-bones created with negatively charged residues of the proteins [66]. According to [PERSON] [67], hydrogen bonds provide stability to the complex ligand-receptor and play a key role in molecular recognition. Moreover, the effective binding of compounds of EOs results in conformational changes in the proteins [68]. Selective metabolites produced by lactic acid bacteria can also bind simultaneously to different QS receptors. The affinity of 3-benzene lactic acids from _Lactobacillus_ spp. for RhlR and PqsR receptors is higher compared to C4-HSL and PQS ligands in _P. aeruginosa_[73]. In addition, flavonoids can also non-competitively bind to the LasR receptor and prevent the protein from binding to DNA.