Discovering, Characterizing, and Applying Acyl Homoserine Lactone-Quenching Enzymes to Mitigate Microbe-Associated Problems Under Saline Conditions

Abstract

Quorum quenching (QQ) is proposed as a new strategy for mitigating microbe-associated problems (e.g., fouling, biocorrosion). However, most QQ agents reported to date have not been evaluated for their quenching efficacies under conditions representative of seawater desalination plants, cooling towers or marine aquaculture. In this study, bacterial strains were isolated from Saudi Arabian coastal environments and screened for acyl homoserine lactone (AHL)-quenching activities. Five AHL quenching bacterial isolates from the genera Pseudoalteromonas, Pontibacillus , and Altererythrobacter exhibited high AHL-quenching activity at a salinity level of 58 g/L and a pH of 7.8 at 50°C. This result demonstrates the potential use of these QQ bacteria in mitigating microbe-associated problems under saline and alkaline conditions at high (>37°C) temperatures. Further characterizations of the QQ efficacies revealed two bacterial isolates, namely, Pseudoalteromonas sp. L11 and Altererythrobacter sp. S1-5, which could possess enzymatic QQ activity. The genome sequences of L11 and S1-5 with a homologous screening against reported AHL quenching genes suggest the existence of four possible QQ coding genes in each strain. Specifically, two novel AHL enzymes, AiiA S1-5 and Est S1-5 from Altererythrobacter sp. S1-5, both contain signal peptides and exhibit QQ activity over a broad range of pH, salinity, and temperature values. In particular, AiiA S1-5 demonstrated activity against a wide spectrum of AHL molecules. When tested against three bacterial species, namely, Aeromonas hydrophila, Pseudomonas aeruginosa , and Vibrio alginolyticus , AiiA S1-5 was able to inhibit the motility of all three species under saline conditions. The biofilm formation associated with P. aeruginosa was also significantly inhibited by AiiA S1-5 . AiiA S1-5 also reduced the quorum sensing-mediated virulence traits of A. hydrophila, P. aeruginosa , and V. alginolyticus during the mid and late exponential phases of cell growth. The enzyme did not impose any detrimental effects on cell growth, suggesting a lower potential for the target bacterium to develop resistance over long-term exposure. Overall, this study suggested that some QQ enzymes obtained from the bacteria that inhabit saline environments under high temperatures have potential applications in the mitigation of microbe-associated problems.

Recombinant N-acyl homoserine lactone-Lactonase AiiAQSI-1 Attenuates Aeromonas hydrophila Virulence Factors, Biofilm Formation and Reduces Mortality in Crucian Carp

“…In some organisms, notably Pseudomonas aeruginosa , biofilm-mediated antibiotic tolerance is regulated by QS in that QS mutants as well as QS inhibition can increase biofilm susceptibility to antibiotics [7]. Thus, the QQ demonstrated by AiiA QSI-1 (this study) and other QQ agents [21,22,27,28,29] has the added potential benefit of reducing antibiotic resistance in A. hydrophila biofilms as well as reducing A. hydrophila virulence. There are several issues that would need to be addressed in pilot-scale studies.…”

“…Our results are in agreement with other in vitro investigations of QQ reduction in virulence in several aquaculture relevant pathogens. Wang et al [21] demonstrated that AiiA S1-5 from Altererythrobacter sp. S1-5 showed the QQ efficacy against quorum sensing-mediated virulence traits of A. hydrophila and Vibrio alginolyticus , such as motility and biofilm formation.…”

Use of Quorum Sensing Inhibition Strategies to Control Microfouling

“…Although it is known that culture conditions can have a high impact on QS-QQ systems, biofilm formation, and/or surface attachment [ 12 , 22 , 23 ], little attention is usually paid to this important factor when a methodology is established. Although the QQ activity in Pseudoalteromonas species is not new and the presence of QQ genes has been reported in previous studies [ 64 , 68 , 69 , 70 ], the effect of the culture medium on QQ capability in this genus has not yet been described, to the best of our knowledge, and deserves more attention. Regarding the Vibrio strains, V. tubiashii also interfered with C12-HSL, but only when cultured in MB.…”

Engineering acyl-homoserine lactone-interfering enzymes toward bacterial control

“…4A). Usually in reporter strains, the gene coding for the QS regulator is cloned together with one of its target promoters (most commonly the promoter of the cognate AHL synthase) upstream of a reporter gene or operon, such as luciferase (32)(33)(34), b-gal (35,36), or fluorescent marker (e.g. GFP) (37,38) (Fig.…”