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. 2016 Nov 23;57(1):100–108. doi: 10.1007/s12088-016-0633-1

Multiplicity of Quorum Quenching Enzymes: A Potential Mechanism to Limit Quorum Sensing Bacterial Population

Shikha Koul 1,2, Vipin Chandra Kalia 1,2,✉
PMCID: PMC5243254  PMID: 28148985

Abstract

Bacteria express certain of their characteristics especially, pathogenicity factors at high cell densities. The process is termed as quorum sensing (QS). QS operates via signal molecules such as acylhomoserine lactones (AHLs). Other bacteria inhibit QS through the inactivation of AHL signals by producing enzymes like AHL-lactonases and -acylases. Comparative genomic analysis has revealed the multiplicity of genes for AHL lactonases (up to 12 copies per genome) among Bacillus spp. and that of AHL-acylases (up to 5 copies per genome) among Pseudomonas spp. This genetic evolution can be envisaged to enable host to withstand the attacks from bacterial population, which regulates its functioning through QS.

Keywords: Acylase, Bacteria, Lactonase, Pathogenicity, Quorum quenching, Quorum sensing

Introduction

Bacteria within a community depend upon each other for their survival. However, to maintain their identity and to ensure their existence they produce an arsenal of bioactive molecules [1–3]. The bacterial arsenal consists of antibiotics, toxins, hydrolytic enzymes, antipathogenic and antibacterial molecules [4–6]. Vibrio spp. fight their competitors through toxin loaded molecular guns—the Type III and VI secretion system (T3SS, T6SS) [7, 8]. Pseudomonas spp. possess the unique ability to produce antibiotics and other pathogenicity factors such as proteases, elastase, rhamnolipid, pyocyanin, superoxide dismutases for their defense against reactive oxygen species (ROS), to evade the immune response, and degrade surfactant proteins [9]. Most of these pathogenicity factors are produced through the phenomenon of quorum sensing (QS) [10, 11]. QS is a cell density dependent phenomenon, which operates through signal molecules. Above a threshold concentration, these signal molecules lead to the expression of selective genes, including those responsible for virulence [12, 13]. QS systems (QSS) such as LuxI/R and their homologs range from a single in Vibrio species to multiple in Sinorhizobium and Pseudomonas species. Each QSS is operated by its unique signal molecule, such as acyl-homoserine lactones (AHLs), oligopeptides, methyl esters, methyl dodecanoic acid, etc. AHLs consist of a lactone ring attached to a carbon side chain, which range from C4 to C18 in length. In this category of AHLs, the most prevalent ones are: N-butanoyl-homoserine lactone (C4HSL), N-hexanoyl-HSL (C6HSL), N-octanoyl-HSL (C8HSL) and N-dodecanoyl-HSL (C12HSL) [14, 15]. Multiplicity of QSS and variability in the signal molecules allow bacteria to use these in various combinations and permutations. This raises the complexity of the mechanisms responsible for controlling the pathogenicity of such bacteria [16–19].

To counter the bacterial population operating through QS mediated mechanism, rival bacteria produce enzymes—AHL-lactonases and -acylases for the AHL-degradation leading to disruption of QS, also called as Quorum Sensing inhibitors (QSIs) [14, 20, 21]. The AHL-lactonases hydrolyze the lactone ring of AHLs and are found in numerous Bacillus spp. [22–24]. Similarly, the AHL-acylases break the amide linkages of the AHL acyl chains and have been reported to be produced by bacteria such as Ralstonia spp. [25, 26]. Although, most bacteria possess one of these QSI enzymes, only a few of them have been reported to possess both AHL-lactonase and AHL-acylase, e.g., Rhodococcus erythropolis, Deinococcus radiodurans, Photorhabdus luminescens, Hyphomonas neptunium [14, 20, 27].

Based on the observations that there is a multiplicity of QSS and QSIs, we did a comparative genomic analysis to explore the possibility of the existence of multiplicity of genes governing the expression of AHL-lactonases and AHL-acylases. This information will further elucidate how this genetic material helps the host to withstand the attacks from bacterial population, which regulates its functioning through QS.

Materials and Methods

Conserved Domains of Acyl-Homoserine Lactone Degrading Enzymes

The detailed procedures used in this study are as described earlier [20]. Briefly, protein sequences for the enzymes AHL-lactonase from Bacillus sp. SB4 (Accession No. AAR85482.1) and AHL-acylase from Ralstonia sp. XJ12B (Accession No. AAO41113.1) were collected from the NCBI Protein database. The nucleotide sequences which corresponded to the protein sequences were downloaded from NCBI Genbank. The conserved domains of these enzymes for reference organisms (Tables 1, 2) are as described in our previous study [20]. We used BLASTP for the similarity searches and NCBI Conserved Domains [28, 29] for searching the conserved domains. The sequences showing multiple copies of AHL-lactonase and AHL-acylase have been analysed here.

Table 1.

Taxonomic distribution of organisms showing multiplicity of AHL lactonase

Organism Enzyme CDa GI No:
Gram positive bacteria
Firmicutes
 Bacillus cereus AiiA Full (F) gi|22095307|gb|AAM92142.1|
AiiA gi|62945899|gb|AAY22194.1|
AHL-lactonase gi|19773609|gb|AAL98724.1|
AHL-lactonase gi|66576020|gb|AAY51613.1|
AHL-lactonase gi|115418822|emb|CAJ84442.1|
 B. cereus G9842b Metal-dependent hydrolase (MDH) F gi|168144103|ref|ZP_02587332.1|
 B. cereus H3081.97b AHL-lactonase Partial (P) gi|206975410|ref|ZP_03236323.1|
 B. cereus ATCC 14579 AHL-hydrolase F gi|30021556|ref|NP_833187.1|
gi|30021556|ref|NP_833187.1|
MDH gi|30022770|ref|NP_834401.1|
 B. cereus B4264 AHL-hydrolase F gi|168133282|ref|ZP_02576511.1|
MDH P gi|168137760|ref|ZP_02580989.1|
 Bacillus sp. 240B1b MDH F, P gi|7416989|gb|AAF62398.1|
 Bacillus sp. 42b AHL-lactonase F gi|146743333|gb|ABQ42909.1|
 Bacillus sp. 91b AHL-lactonase F gi|146743335|gb|ABQ42910.1|
 Bacillus sp. A24 AiiA F, P gi|21541343|gb|AAM61772.1
 Bacillus sp. COT1b AHL-lactonase F gi|19773593|gb|AAL98716.1|
 Bacillus sp. CSX-1b AHL-hydrolase F gi|109809891|gb|ABG46349.1|
 Bacillus sp. SB4b AHL-lactonase F gi|40388447|gb|AAR85482.1|
 Bacillus sp. B14905 HP BB14905_11105 F gi|126653419|ref|ZP_01725520.1|
YtnP gi|126651311|ref|ZP_01723518.1|
 B. subtilis AHL-lactonase F gi|66576014|gb|AAY51610.1|
gi|66576016|gb|AAY51611.1|
gi|150256376|gb|ABR68029.1|
 B. thuringiensis AHL-lactonase F gi|19773603|gb|AAL98721.1
gi|19773605|gb|AAL98722.1
gi|19773595|gb|AAL98717.1|
gi|19773599|gb|AAL98719.1|
gi|19773601|gb|AAL98720.1|
 B. thuringiensis AHL-lactonase F gi|66576018|gb|AAY51612.1|
gi|34500091|gb|AAQ73629.1|
gi|34500091|gb|AAQ73629.1|
gi|90421378|gb|ABD93926.1|
gi|67107096|gb|AAY67830.1|
gi|90421372|gb|ABD93923.1|
gi|124389890|gb|ABN11118.1|
gi|90421376|gb|ABD93925.1|
gi|197253281|gb|ACH54082.1|
gi|38564660|gb|AAR23790.1|
F, P gi|90421370|gb|ABD93922.1|
gi|90421374|gb|ABD93924.1|
P(2) gi|146743337|gb|ABQ42911.1|
 B. thuringiensis AiiA F gi|209944153|gb|ACI96332.1|
gi|209944159|gb|ACI96335.1|
gi|209944167|gb|ACI96339.1|
gi|209944163|gb|ACI96337.1|
gi|209944151|gb|ACI96331.1|
gi|209944161|gb|ACI96336.1|
gi|209944165|gb|ACI96338.1|
gi|209944169|gb|ACI96340.1|
gi|209944155|gb|ACI96333.1|
gi|209944157|gb|ACI96334.1|
gi|209944171|gb|ACI96341.1|
gi|209944173|gb|ACI96342.1|
 B. thuringiensis AHL-lactonase F gi|194709246|pdb|3DHA|
gi|85544298|pdb|2BR6|
gi|125711135|gb|ABN51242.1|
 B. thuringiensis serovar canadensis AiiA-like protein F gi|22095279|gb|AAM92128.1|
 B. thuringiensis serovar galleriae AiiA-like protein gi|22095283|gb|AAM92130.1|
 B. thuringiensis serovar kyushuensis AiiA-like protein gi|22095289|gb|AAM92133.1|
 B. thuringiensis serovar ostriniae AiiA-like protein gi|22095293|gb|AAM92135.1|
 B. thuringiensis serovar pakistani AiiA-like protein gi|22095295|gb|AAM92136.1|
 B. thuringiensis serovar toumanoffi AiiA-like protein gi|22095301|gb|AAM92139.1|
 B. thuringiensis serovar japonensis AHL-lactonase gi|33187780|gb|AAP97743.1|
 B. thuringiensis serovar kim AHL-lactonase gi|33187778|gb|AAP97742.1|
 B. thuringiensis serovar jinhongiensis AiiA-like enzyme gi|28413984|gb|AAO40748.1|
 B. thuringiensis serovar oswaldocruzi AiiA-like enzyme gi|28413776|gb|AAO40747.1|
 B. thuringiensis serovar kurstaki AHL-hydrolase gi|75766091|pdb|2A7 M|
 B. thuringiensis serovar alesti AHL-hydrolase gi|124014030|gb|ABM88266.1|
 B. thuringiensis str. Al Hakam MDH gi|118479835|ref|YP_896986.1|
 B. thuringiensis serovar israelensis ATCC 35646 AHL-hydrolase F gi|75761848|ref|ZP_00741777.1|
MDH gi|75761592|ref|ZP_00741546.1|
 Lysinibacillus sphaericus C3-41 HP Bsph_3377 F gi|169828841|ref|YP_001698999.1|
YtnP gi|169829648|ref|YP_001699806.1|
Deinococcus-Thermus
 Deinococcus radiodurans R1 Hypothetical protein (HP) DR_0172 F gi|15805209|ref|NP_293896.1|
HP DR_1823 gi|15806823|ref|NP_295546.1|
Gram negative bacteria
Alphaproteobacteria
 Agrobacterium tumefaciens str. C58 MDH F gi|16119885|ref|NP_396590.1|
MDH P gi|159186505|ref|NP_396071.2|
 A. tumefaciens b AttM/AiiB P gi|17223785|gb|AAL13075.1|
 BradyRhizobium sp. ORS278 putative metallo-beta-lactamase family protein F gi|146341021|ref|YP_001206069.1|
putative MDH gi|146343732|ref|YP_001208780.1|
putative signal peptide gi|146339571|ref|YP_001204619.1|
 BradyRhizobium japonicum b AttM-like protein F gi|6655034|gb|AAF22881.1|
 B. japonicum USDA 110b AttM/AiiB family protein F gi|27380160|ref|NP_771689.1|
Euryarchaeota
 Thermoplasma volcanium GSS1 MDH (AttM-related) F gi|13542116|ref|NP_111804.1|
MDH gi|13541013|ref|NP_110701.1|
HP gi|14324397|dbj|BAB59325.1|
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aReference organism used was Bacillus sp. SB4 (Accession No. AAR854821) for searching Conserved Domains (CDs) of Lactamase_B, superfamily

bThis information has been retained in the Table to show variability in copy number in different species of a given Genus

Table 2.

Taxonomic distribution of organisms showing multiplicity of AHL-acylase

Organism Enzyme CDa GI No:
Gram-negative
Betaproteobacteria
 Ralstonia sp. XJ12Ba AHL-acylase Partial (P(2)) gi|28376389|gb|AAO41113.1|
 Ralstonia eutropha JMP134b Penicillin amidase (PAM) P gi|73541530|ref|YP_296050.1|
 R. eutropha H16b PAM or acylase (PAC) P(2) gi|113867898|ref|YP_726387.1|
 R. pickettii 12Jb Peptidase S45, PAM P(2) gi|187929893|ref|YP_001900380.1|
 R. solanacearum GMI1000b Aculeacin A acylase P(2) gi|17547266|ref|NP_520668.1|
 R. metallidurans CH34b Peptidase S45, PAM P(2) gi|94313782|ref|YP_586991.1|
 R. pickettii 12D Peptidase S45, PAM P(2) gi|153885673|ref|ZP_02006829.1|
Aculeacin A acylase P(2) gi|153885674|ref|ZP_02006830.1|
Gammaproteobacteria
 Azotobacter vinelandii AvOP Peptidase S45, PAM P(2) gi|67157312|ref|ZP_00418614.1|
P gi|67157375|ref|ZP_00418677.1|
 Pseudomonas sp. SY-77-1 Glutaryl-7-amino-cephalosporanic-acid acylase P(2) gi|116242485|sp|P07662.2|
Chain A P(2) gi|47168470|pdb|1OQZ|
Chain B P gi|47168473|pdb|1OR0|B
 Pseudomonas aeruginosa PAO1 AHL acylase PvdQ P(2) gi|15597581|ref|NP_251075.1|
Hypo. protein (HP) PA1893 P gi|15597090|ref|NP_250584.1|
 P. aeruginosa PA7 AHL acylase P(2) gi|152987503|ref|YP_001348236.1|
HP PSPA7_3392 P gi|152987014|ref|YP_001348752.1|
Putative PAM P gi|152985857|ref|YP_001349702.1|
 P. aeruginosa PACS2 HP PaerPA_01002361 P gi|107101327|ref|ZP_01365245.1|
HP PaerPA_01002874 P(2) gi|107101829|ref|ZP_01365747.1|
HP PaerPA_01001501 P gi|107100476|ref|ZP_01364394.1|
 P. aeruginosa UCBPP-PA14 PAC P(2) gi|116050326|ref|YP_790857.1|
HP PA14_40040 P gi|116049847|ref|YP_791346.1|
PAM P gi|116048960|ref|YP_792238.1|
 P. aeruginosa 2192 PvdQ P(2) gi|194551803|ref|YP_002086830.1|
HP PA2G_00931 P gi|194551272|ref|YP_002086299.1|
 P. aeruginosa C3719 HP PACG_00864 P gi|194545971|ref|YP_002080999.1|
HP PACG_00002 P gi|194545153|ref|YP_002080181.1|
PvdQ P(2) gi|194546375|ref|YP_002081403.1|
 P. entomophila L48 PAM P(2) gi|104781218|ref|YP_607716.1|
AHL-acylase Full (F),P gi|104784167|ref|YP_610665.1|
 P. fluorescens Pf-5 PAM P(2) gi|70730269|ref|YP_260008.1|
P gi|70733204|ref|YP_262977.1|
 P. fluorescens Pf0-1 Peptidase S45 P(2) gi|77458788|ref|YP_348294.1|
PAM, SepQ protein F,P gi|77457440|ref|YP_346945.1|
 P. mendocina ymp b Peptidase S45, PAM P gi|146309254|ref|YP_001189719.1|
 P. putida F1 Peptidase S45, PAM P(2) gi|148548004|ref|YP_001268106.1|
P gi|148550271|ref|YP_001270373.1|
 P. putida GB-1 Peptidase S45, PAM P(2) gi|167033881|ref|YP_001669112.1|
P gi|167036204|ref|YP_001671435.1|
 P. putida W619 Peptidase S45, PAM P(2) gi|170721584|ref|YP_001749272.1|
P gi|170719488|ref|YP_001747176.1|
 P. syringae pv. phaseolicola 1448Ab PAM P(2) gi|71736215|ref|YP_274165.1|
 P. syringae pv. syringae str. B728ab Peptidase S45, PAM P(2) gi|66045211|ref|YP_235052.1|
 P. syringae pv. tomato str. DC3000b PAM P(2) gi|28869364|ref|NP_791983.1|
 Shewanella benthica KT99 Aculeacin A acylase P(2) gi|163749206|ref|ZP_02156456.1|
P(2) gi|163749207|ref|ZP_02156457.1|
Gamma proteobacterium KT 71 Peptidase S45, PAM F gi|88703935|ref|ZP_01101650.1|
P gi|88706973|ref|ZP_01104671.1|
P(2) gi|88706945|ref|ZP_01104644.1|
Marine Gamma proteobacterium HTCC2080 Aculeacin A acylase F, P(2) gi|119505017|ref|ZP_01627093.1|
PAM P gi|119504715|ref|ZP_01626793.1|
Deltaproteobacteria
 Plesiocystis pacifica SIR-1 PAM, PAC F, P(2) gi|149923822|ref|ZP_01912213.1|
F gi|149917617|ref|ZP_01906114.1|
Stigmatella aurantiaca DW4/3-1 Aculeacin A acylase P(2) gi|115376563|ref|ZP_01463795.1|
P(2) gi|115378259|ref|ZP_01465428.1|
Gram-positive
Deinococcus
 Deinococcus radiodurans R1b Aculeacin A acylase P(2) gi|15807918|ref|NP_285578.1|
Actinobacteria
 Nocardioides sp. JS614 Peptidase S45, Penicillin Amidase (PAM) P(2) gi|119717562|ref|YP_924527.1|
P(2) gi|119715569|ref|YP_922534.1|
 Streptomyces sp. Mg1 PAM F, P(2) gi|197333590|ref|ZP_03175656.1|
Putative acylase F, P(2) gi|197754175|ref|YP_002177538.1|
 Streptomyces griseus subsp. griseus NBRC 13350 PAM P(2) gi|182440602|ref|YP_001828321.1|
Putative acylase P gi|182438087|ref|YP_001825806.1|
 S. sviceus ATCC 29083 PAM F, P(2) gi|197933677|ref|ZP_03197971.1|
Putative acylase P(2) gi|197780832|ref|YP_002203628.1|
Cyanobacteria
 Cyanothece sp. PCC 7424 Glutaryl-7-amino-cephalosporanic-acid acylase F,P gi|186900662|ref|ZP_02973619.1|
Peptidase S45, PAM P(2) gi|186902234|ref|ZP_02975180.1|
 Crocosphaera watsonii WH 8501 AHL-acylase P(2) gi|67923096|ref|ZP_00516587.1|
F gi|67923095|ref|ZP_00516586.1|
Chloroflexi
 Chloroflexus aurantiacus J-10-fl Peptidase S45, PAM P gi|163847876|ref|YP_001635920.1|
P gi|163849271|ref|YP_001637315.1|
 Herpetosiphon aurantiacus ATCC 23779 peptidase S45, PAM P gi|159898624|ref|YP_001544871.1|
P gi|159901506|ref|YP_001547753.1|
Bacteroidetes
 Robiginitalea biformata HTCC2501 PAM P(2) gi|88805528|ref|ZP_01121047.1|
P gi|88804265|ref|ZP_01119785.1|
P(2) gi|88804870|ref|ZP_01120390.1|
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aReference organism used was Ralstonia sp. XJ12B (Accession No. AAO41113.1) for searching Conserved Domains (CDs) of Ntn_hydrolase superfamily

bThis information has been retained in the Table to show variability in copy number in different species of a given Genus

Results

The presence of genes encoding for AHL-lactonase and -acylase has been observed in taxonomically diverse bacteria: gram-positive and -negative groups [20]. In the present study, the focus has been on identifying organisms with multiple copies of genes for AHL-lactonase and AHL-acylase.

Multiplicity of Genes Coding for AHL-Lactonase

Among all those organisms which show the presence of conserved domains for the enzyme—AHL-lactonase, the highest prevalence of the gene for this enzyme was recorded in Firmicutes (Gram-positive) and Proteobacteria (Gram-negative). Among Gram-positive bacteria, multiplicity of the gene for AHL-lactonase was recorded in (a) Firmicutes—(1) Bacillus spp., and (2) Lysinibacillus, and (b) Deinococcus thermus—D. radiodurans (Table 1). Interestingly, within Bacillus spp., (1) B. cereus strains were quite unique, where some showed a single copy of the gene for AHL-lactonase, whereas others possessed 2–5 copies of the same, (2) the strains of B. subtilis had 3 copies per genome, and (3) B. thuringiensis strains had 1–12 copies per genome. On the other hand, among Gram-negative bacteria, Agrobacterium sp. and Bradyrhizobium sp. had single and multiple copies of the gene for AHL-lactonase. Apart from these bacteria, Thermoplasma was observed to possess 3 copies of AttM related AHL-lactonase gene (Table 1).

Multiplicity of Genes Coding for AHL-Acylase

Multiple copies of gene coding for AHL-acylase, were found to be distributed among gram-negative bacteria representing different taxa: β-, γ-, and δ-Proteobacteria (Table 2). Ralstonia sp. XJ112B is known to possess active AHL-acylase and within the conserved domain of Ntn-hydrolase superfamily, represented by two partial domains. Ralstonia sp. in general have been observed to possess single copies of the gene coding for AHL-acylase, except Ralstonia picketti 12D, which possesses two copies (denoted by different gi numbers), within the sequenced genome. Among the members of γ-Proteobacteria, (1) Azotobacter vinelandii, (2) Pseudomonas sp., (3) P. aeruginosa strains PAO1, PA7, PACS2, UCBPP-PA14, 2197 and C379, (4) P. entomophila, (5) P. fluorescens, (6) P. putida strains F1, GB,W619, (7) P. syringae strains Phaseolicola 448A, syringae B728a, and tomato str. DC3000, (8) Marine proteobacterium exhibits multiple copies of this gene per genome.

Similarly, in gram-positive organisms multiplicity of the gene for AHL-acylase was recorded in (a) Deinococcus—D. radiodurans R1, (b) Actinobacteria—Streptomyces sp. Mg1, Streptomyces griseus subsp. griseus NBRC 13350 (c) Cyanobacteria—Cyanothece sp. PCC 7424, Crocosphaera watsonii WH 8501 (Table 2).

Discussion

Biological control of diseases caused by pathogenic bacteria such as Pseudomonas spp. in soil or rhizosphere has been reported with the help of rhizobacteria, e.g., Bacillus spp. [3, 30]. Bacillus spp. have been shown to control pathogens such as Erwinia caratovora, [31], Xanthomonas campesteris [32], Phytophthora infestens [33], P. syringae [34]. Heterologous expression of Bacillus AiiA lactonase in Burkholderia thailandensis, P. aeruginosa PAO1, Vibrio harveyi, and E. carotovora have been found to disrupt QS mediated properties [35, 36]. In fact, certain antibiotics become effective on biofilms, which have been exposed to AHL degrading enzymes, which implies that a combination of the two treatments can be complementary and effective in controlling the pathogenic organism(s) [30].

The presence of AHL lactonase throughout the gram positive genus—Bacillus shows the evolutionary stability of the aiiA gene. B. thuringiensis has been observed to exhibit a maximum of 12 copies of the complete AHL lactonase gene and B. cereus with 5 copies. In case of the gram negative group, taxa wide horizontal gene transfer (HGT) is suggested by the presence of the lactonase from Agrobacterium tumifaciens and Bradyrhizobium sp. (α-Proteobacteria), into Thermoplasma volcanium belonging to Euryarchaeota. Potential cases of HGT have been reported in the case of AHL-lactonase, where Moorella sp. (Firmicutes) and Burkholderia sp. (β-Proteobacteria) were found to show high phylogenetic similarity. Similarly, (1) Mycobacterium sp. and Rubrobacter sp. belonging to Actinobacteria were proposed to have shared this gene with the members of α-Proteobacteria (Granulibacter sp., Acidiphilum sp. and A. tumefaciens), and (2) D. radiodurans (Deinococcus-Thermus) and Xylella fastidiosa (γ-Proteobacteria) [20].

In the case of AHL-acylases, Ralstonia sp., contains an assortment of enzymes AHL-acylase, Penicillin amidase (PAM), Peptidase and Aculeacin A acylase. PAM in addition to the peptidase, can be seen to be distributed through gram negative as well as gram positive taxas. This is indicative of HGT in the case of AHL-Acylase as well. In fact, previous study has proposed HGT between members of (1) Acidobacteria and δ-Proteobacteria, and (2) D. radiodurans and Ralstonia spp. (β-Proteobacteria) [20]. A maximum of 5 copies of PAM is present in the Bacteriodetes, Robiginitalea biformata followed by the Actinobacteria, Nocardioides sp. JS614 having 4 copies. γ-Proteobacteria KT-71, contains 4 copies of peptidase and PAM. The major carrier of multiple gene copies has been found to be the Pseudomonas sp. in γ-Proteobacteria, majorly having peptidase.

AHL-lactonase and -acylase have been proved to inhibit bacterial infections, and prevent biofilm growth, etc. It may be professed that the hydrolysis of the lactone ring is an efficient method for Quorum Quenching (QQ) [19, 20]. In future, these genes may acquire novel functions beneficial for the survival of the host, as in the unique case of mammalian paraoxonases (PONs). It has been speculated that these AHL-lactonases have emerged within three super-families through convergent/parallel evolution [22, 37–39]. It is further stated that PONs have evolved from lactonases only after the introduction of the parathion, an organophosphate pesticide [38–40]. The evolutionary significance of lactonases has been found to be established in mammals, where they subsequently acquired the detoxifying functions to act as a tool of innate immunity [41]. The present classes of mammalian PONs: (1) PON1 (2) PON2 (3) PON3 have been shown to have originated from bacterial lactonases via horizontal gene transfer from an endosymbiotic bacteria. They still exhibit the presence of ancestral AHL lactonase relics in association with their detoxification characteristics [41]. PON2 however, seems to have gained new functions and has also reverted to the ancestral AHL lactonase activity [41].

In the face of increasing antibiotic resistance alternate therapy approaches need to be developed. QQ enzymes from a diverse range of organisms can be used for this purpose. The activity of AHL lactonase is lactone ring specific and not dependent upon the acyl chain length, in the case of AHL acylase [19, 20]. As elucidated in QSSs, such a multiplicity has been observed here for AHL-lactonase and AHL-acylase as well. In the virtual battle going on in the environment between QS and QSIs, in contrast to antibiotics, QSIs act at very low concentrations without killing the bacteria. This does not generate the pressure on bacteria to develop resistance against antibiotics. The implications of this diversity and multiplicity of AHL-lactonases and -acylases along with HGT and continuous gain of new favourable functions, as a weapon to interfere with QS opens a new paradigm of evolutionary benefits to the host and therein may lie our answer for antibiotic resistance.

Conclusion

We have been able to elucidate the presence of multiple copies of AHL-lactonase and -acylase in diverse organisms. These genes may acquire novel functions to increase the fitness of the host organisms against those organisms, which operate specific functions through QS. Bacillus sp. being designated as GRAS (Generally Regarded As Safe) by the FDA and an industrial workhorse, is also the predominant species that produces lactonase and has a great potential in this field.

Acknowledgements

We are thankful to the Director of CSIR Institute of Genomics and Integrative Biology (IGIB), and CSIR Project INDEPTH (BSC0111) for providing the necessary funds, facilities and moral support.

Compliance with ethical standards

Conflict of interest

All authors declare no conflicts of interest in this paper.

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