ARTÍCULO DE INVESTIGACIÓN

Identification, cloning and lactonase activity of recombinant

protein of N-acyl homoserine lactonase (AiiA) from Bacillus
thuringiensis 147-115-16 strain
Identificación, clonación y actividad lactonasa de la proteína
recombinante de N-ácil homoserina lactonasa (AiiA)
de Bacillus thuringiensis cepa 147-115-16
Álvaro M. Florez*|, Adriana González*, Carmen J. Pedroza**, Elizabeth Correa**,
Nohora J. Rueda*, Sergio Orduz**

Abstract
The quorum-quenching N-acyl homoserine lactonases are a family of bacterial metalloenzymes that participate in degra-
dation of N-acyl homoserine lactones (AHLs), disrupting the quorum sensing system of gram negative bacterial species.
From a collection of Bacillus thuringiensis strains isolated in Colombia from plants and exhibiting toxic activity against lepi-
dopteran insects, 310 bacterial isolates were tested to determine lactonase activity by using biosensor systems in presence
of synthetic N-hexanoyl-L-homoserine lactone (C6-HSL) and N-octanoyl-L-homoserine lactone (C8-HSL). From them, 251
strains showed degrading activity to both C6-HSL and C8-HSL, 57% exhibited degrading activity to C6-HSL and 43% to
C8-HSL. One B. thuringiensis strain, denoted as 147-115-16, that exhibit high degrading activity to C6-HSL and C8-HSL,
was able to attenuate soft rot symptoms in infected potato slices with Pectobacterium carotovorum. This strain contains an
homologous of the aiiA gene that was cloned, sequenced and expressed in Esherichia coli DE3. The recombinant protein
AiiA147-11516 display activity to C6-HSL, C8-HSL, N-(β-ketocaproyl) (3-O-C6-HSL) and N-3-oxo-dodecanoyl (3-O-C12-HSL).
The recombinant strain in the presence of P. caratovorum cultures was able to attenuate the infection, suggesting that it
interferes either on the accumulation or response to the AHLs signals. Acording to this data and based on previous report
from recombinant AiiA147-11516, this enzyme exhibit activity to wide range of catalytic substrates suggesting its industrial
application in the disease control programs by plants transformation.
Key words: lactones, Quorum sensing, Quorum quenching, Lactonases, Pectobacterium caratovorum

Resumen
Las N-acíl homoserina lactonasas son una familia de metaloenzimas bacterianas que participan en la degradación de N-acil
homoserina lactonas (AHLs) interrumpiendo el sistema de detección de quórum sensing de bacterias Gram negativas. A
partir de una colección de cepas de Bacillus thuringiensis aisladas del filoplano de plantas colombianas que presentaron
actividad tóxina contra insectos lepidópteros, 310 fueron probadas para determinar actividad lactonasa mediante el uso de
sistemas de biosensores en presencia de N-hexanoilo-L-homoserina lactona (C6-HSL) y la N-octanoilo-L-homoserina lactona
(C8-HSL) sintéticas. De estas cepas, el 251 mostraron actividad para ambas lactonas y de estas, el 57% mostró actividad a
C6-HSL y el 43% a C8-HSL. Una cepa de B. thuringiensis- denominada 147-115-16- que mostró alta actividad para C6-HSL
y C8-HSL, fue capaz de atenuar los síntomas de la pudrición blanda en rodajas de papa infectadas con Pectobacterium
carotovorum. Esta cepa contiene un gen homólogo a aiiA, el cual este fue clonado, secuenciado y expresado en Escherichia
coli DE3. La proteína recombinante AiiA147-11516 exhibe actividad para C6-HSL y C8-HSL, así como para N-(β-cetocaproil)
(3-O-C6-HSL) y N-3-oxo-dodecanoil (3-O-C12-HSL). La cepa recombinante en presencia de P. caratovorum fue capaz de
atenuar la infección, sugiriendo que interfiere con la acumulación o respuesta de las señales AHLs. Según estos datos y

* Laboratorio de Biología Molecular y Biotecnología, Instituto MASIRA, Facultad de Salud, Universidad de Santander, UDES, Bucaramanga,
Santander, Colombia.
** Escuela de Biociencias, Facultad de Ciencias, Universidad Nacional de Colombia sede Medellin, Medellin, Colombia.
| Correspondence author amflorez@udes.edu.co. Phone +57 6516500 Ext. 1375. Fax: +57 6516492

Rev. Colomb. Biotecnol. Vol. XVI No. 1 Julio 2014 153-162 153
 basados en el reporte previo sobre la actividad hidrolítica de la proteína recombinante AiiA147-11516, esta enzima posee un
actividad contra un amplio número de sustratos lo cual sugiere su aplicación en la industria en el control de enfermedades,
mediante la transformación de plantas.
Palabras clave: Lactones, Quorum sensing, Quorum quenching, Lactonases, Pectobacterium caratovorum.

Recibido: octubre 25 de 2013 Aprobado: mayo de 2014

Introduction (VAI-C), which is capable of using AHLs as a sole nu-

trient source (Leadbetter and Greenberg, 2000).
In the majority of gram negative bacteria quorum sen-
sing is mainly mediated by signaling cascades, invol- Production of QQ N-acyl homoserine-lactonases was
ving N-acyl-homoserine lactones (AHLs) (Von Bodman first reported in a strain of the genus Bacillus sp. (Dong
et al., 2003). AHLs contain a common homoserine et al., 2000; Dong et al., 2004). It was also reported in
lactone ring, differing in their carbon lenght (4 to 18 Bacillus thuringiensis, B. cereus and B. mycoides (Dong
carbons), degree of saturation, and the presence of C3 et al., 2002; Lee et al., 2002). The first AHL-lactonase
acyl chain modifications. AHLs are multifunctional mo- that was completely charaterized was AiiA240B1 and it
lecules that when they accumulate regulate relevant was found hat belongs to the metallo-β-lactamase fa-
functions during bacterial growth such as production mily based on the presence of a HXHXDH motif, and
of extracellular enzymes, bioluminescence, biofilm an identical Zn2+ binding motif (Dong et al., 2000).
formation, and coordinate cellular activities associa- This enzyme has the ability to inactivate AHLs with
ted with host pathogen interactions (Atkinson and different acyl chain lengths and substitutions at the
Williams, 2009; Williams and Camara, 2009). Many C3 position, including N-butyryl-L-homoserine lactone
bacterial species, such as Pectobacterium carotovo- (C4-HSL), 3-O-C6-HSL, 3-O-C8-HSL, and 3-O-C12-HSL
rum, are highly pathogenic to plants by triggering the (Dong et al., 2001).
expression of virulence factors via quorum sensing The second AHL-lactonase (AiiABTK) reported was isola-
(QS) (Williams, 2007). P. caratovorum is an ethiologic ted from B. thuringiensis subsp. kurstaki, and work on a
agent of soft rot disease in a wide variety of cultivated wider range of AHLs substrates, with maximum activity
plants (Charkowski, 2009). This bacterium regulates towards C10-HSL. This enzyme contains two Zn2+ ions
the production of different exoenzymes by secreting into the active site and possesses the same conserved
AHLs, including N-(3-oxohexanoyl)-L-homoserine lac- residues present in all AHL-lactonases whose activity
tone (3-O-C6-HSL) and N-(3-oxooctanoyl)-L-homoseri- depends in metal coordination (Kim et al., 2005). For
ne lactone (3-O-C8-HSL) (Jones et al., 1993; Pirhonen both characterized enzymes, AiiA240B1 and AiiABTK, im-
et al., 1993; Cha et al., 1998; Smadja et al., 2004; Chat- portant differences in the affinity for metal ions under
terjee et al., 2005; Liu et al., 2008). The role of QS chelating agents have been described (Wang et al.,
in P. caratovorum pathogenecity have been reviewed 2004; Kim et al., 2005; Thomas et al., 2005).
(Barnard et al., 2007).
Based on that there is widespread existence of AHL-lac-
In contrast, there are microorganims acting as anta- tonases in B. thuringiensis (Dong et al., 2002; Lee et al.,
gonists of QS by producing signal interference me- 2002), and in Colombia more than 600 B. thuringiensis
chanisms known as quorum quenching (QQ), (Kalia, isolates have been characterized looking for insecticidal
2013) mediated by AHL-degrading enzymes. There are activity (Uribe et al., 2003; Jara et al., 2006; Armengol
two families of QQ enzymes, lactonases and acylases. et al., 2007), we aimed at isolating AHL degrading from
The lactonase family cleaves the lactone ring of AHLs a B. thuringiensis collection obtained from Colombian
releasing N-acyl homoserines, which are not recogni- phyloplane. In this study we screened a B. thuringiensis
zed as a QS signal, some examples include AiiA from collection and described the cloning, sequencing and
Bacillus sp., AttM from Agrobacterium tumefaciens stra- the activity of recombinant protein of a N-acyl homose-
in A60, AiiB from A. tumefaciens strain C58 (Carlier et rine lactonase from B. thuringiensis 147-11516 .
al., 2003; Dong et al., 2000) and AhlD from Arthro-
bacter sp. (Park et al., 2003). Acylases are known to Materials and methods
be capable of cleaving the acyl bonds and releasing
a homoserine lactone ring (Lin et al., 2003; Sio et al., Bacterial strains and growth conditions
2006), some representative enzymes are AiiD from
Ralstonia XJ12B, and PvdQ from Pseudomonas aerugi- Two different AHL biosensors strains were used to
nosa PAO1. After the cleavage of the AHLs molecules, detect AHL-lactonase activity, Chromobacterium viola-
the released products become more soluble in water, ceum CVO26 (mini Tn5 mutant of 31532) (McClean
making them an available nutrient source to the so- et al., 1997; Winson et al., 1998) and A. tumefaciens
rrounding microorganisms, like Variovorax paradoxus NTL4 traI-lacZ fusion (pCF218) (pCF372) (Fuqua et al.,

154 Rev. Colomb. Biotecnol. Vol. XVI No. 1 Julio 2014 153-162
1994). C. violaceum CVO26 was grown in LB medium substrate to either C6-HSL or C8-HSL at 30, 60 and
(1% peptone, 0.5% yeast extract, 0.5% NaCl) solidified 120 min or 60 and 120 min were reported.
with 1.2% agar, and supplemented with kanamycin (20
µg/ml) (Invitrogen®). A. tumefaciens NTL4 was grown
in AT minimal salts medium as was described in Tempé
Screening of AHL production by P. caratovorum
et al. (1977), at 30°C, supplemented with tetracycline The plant pathogenic bacterium P. caratovorum was
4.5 µg/ml (Sigma-Aldrich®), spectinomycin 50 µg/ml streaked in parallel to the biosensor strains in LB agar
(Sigma-Aldrich®) and 40 µg/ml of X-gal (Promega®). Es- for CVO26 and in the same way for NTL4 but in AT
cherichia coli ArticExpress (DE3) cells were used for medium supplemented with 50 µg X-gal (Ravn et al.,
cloning and expression and were cultured at 37°C in 2001; Chu et al., 2011), and plates were incubated
LB medium supplemented with 100 µg/ml of ampici- for 24 h at 30°C. To evaluate the presence of AHLs,
llin (Sigma-Aldrich®). B. thuringiensis strains were cultu- CVO26 was streaked on LB agar supplemented with
red in LB medium at 30°C in agar plates and broth. C6-HSL, because its sensor system is inhibited by long
Plant material with symptoms of soft rot disease were acyl chain molecules. For this last assay, all plates with
selected in order to isolate bacterial plant pathogens as CVO26 were incubated for 24 h at 30°C for produc-
described (Pérombelon and Kelman, 1980). Samples tion of purple pigment, and then plates were re-incu-
were taken from affected zones from lettuce (Lactuca bated at 30°C for 24 h in order to evaluate inhibition
sativa var. Batavia), calla lily (Zantedeschia aethiopica of pigment formation.
var. Spreng), potato (Solanum tuberosum var. Diacol
capiro) and lulo (S. quitoense var. Castilla), and proces- In vitro control of soft rot symptoms
sed according to phytopathological methods (Agrios,
2005). Different bacterial colonies were obtained in To evaluate the effect of AHL-lactonase activity of B.
nutrient agar from serial dilutions of macerated tissues. thuringiensis on P. caratovorum infection, potatoes
The isolated colonies were grown in D-3 selective me- (S. tuberosum var Diacol Capiro) were washed with
dium for P. caratovorum (Kado et al., 1970). Comple- tap water and treated as described Dong et al. (2004).
mentary tests for species identification were carried Five mm thick potato slices were dipped in a B. thurin-
out as described (Schaad et al., 2001). giensis 12 hr culture containing 2x107 CFU/ml for 20 s
and then were air dried in a laminar flow cabinet for
B. thuringiensis AHL-lactonase activity 20 min. Then, three streaks were made on the surface
of the slices and inoculated with 2.5 µl of cell culture
AHL-lactonase activity was evaluated in 310 B. thurin- media containing 1x105 UFC/ml of an P. caratovorum
giensis isolates as described by Lee et al. (2002), with suspension isolated from potato. Each slice was pla-
some modifications. A culture of each B. thuringiensis ced in a petri dish in a humid chamber at 30°C. Di-
strain was grown overnight until reaching an optical sease symtoms were evaluated after 24 and 48 h of
density of 1.1 at 600 nm. Then, 20 µM of synthetic treatment. Each treatment was performed in quadru-
C6-HSL and C8-HSL (Sigma-Aldrich®) were added in- plicate. Based on the severity of the soft rot symptoms
dependently into each culture and the reaction mixtu- produced in the potato slices, a scale was developed
re was incubated at 30ºC with shaking during 30, 60 to qualify the effect of B. thuringiensis on the disease
and 120 min. Bacterial cells were centrifuged at 3000 caused by P. caratovorum. Absence of soft rot was as-
x g for 10 min and the supernatants corresponding signed with (-), presence of small soft rot area and little
to each incubation time and to each B. thuringiensis wet was considered with (+), presence of moderate
strain were heated for 3 min at 95°C and placed into soft rot area, dark and wet was considered with (++)
petri dishes with 10 wells with LB medium or AT agar and, presence of high soft rot area, very dark and very
containing an agar-suspension culture of the biosensor wet was considered with (+++).
strain. These plates were incubated for 24 h at 30°C.
The AHL-lactonase activity was evaluated at different
times by measuring the diameters of the colored areas Cloning and sequencing of the aiiA gene
surrounding the wells in CVO26 (purple) and NTL4 The B. thuringiensis strain displaying greater AHL-lacto-
(blue). Based on the sizes of the colored areas, a scale nase activity with the biosensor strains A. tumefaciens
was designed; diameters between 0.0 and 0.39 cm2 NTL4 and C. violaceum CVO26 and the best control
were assigned with (+++) indicating B. thuringiensis of P. caratovorum pathogenicity was selected and its
strains displaying high AHL-lactonase activity; between DNA was extracted (Ceron et al., 1995). Using PCR
0.4 and 0.74 cm2 were assigned with (++) indicating the aiiA gene was amplified with the following primers:
a moderate activity; and between 0.75 and 0.89 cm2
5´ATCGGATCCATGACAGTAAAGAAGCTTTATTTCG3´a
were assigned with (+) indicating a low activity. Finally,
diameters larger than 0.9 cm2 were considered without nd 5´GTCGAATTCCTCAACAAGATACTCCTAATGATGT3´
designed according to the aiiA sequences previously
AHL-lactonase activity. Only the B. thuringiensis strains
reported (Dong et al., 2002). Amplification conditions
that exhibit high AHL lactonase activity (+++) to each were: denaturation at 94°C for 3 min followed by 28

N-acyl homoserine lactonase (AiiA) from Bacillus thuringiensis 155

cycles at 94°C for 30 s, 50°C for 30 s, and 72°C for DE3 strain and P. caratovorum alone as negative control.
1 min in a MJ Research Thermocycler (Bio-Rad®). The Once the incubation time was finished each culture was
amplified fragments were purified with a QIAquick PCR centrifuged at 5800 x g during 10 min at 21°C and the
purification system (Qiagen®) and cloned into pGEM- supernatants were collected. Six lines were made with
T vector (Promega®). Clones were selected in LB me- a sterile blade on each petri dish containing either LB
dia supplemented with IPTG (40 µg/ml) (Invitrogen®), media for CV026 strain or AB media with X-gal for NTL4
X-gal (40 µg/ml) (Invitrogen®) and ampicillin (100 µg/ strain. Each line was 1 cm wide and 3 mm apart. Five
ml) (Sigma-Aldrich®). The gene was sequenced in both µL of each supernatant was served in one end of each
strands and the results were analyzed using Blastn, groove, and the samples were allowed to dry, and then
Blastp and ClustalW algorithm in Bioedit (Hall, 1999). each respective reporter strain was streaked. The petri
The similarity and identity analyses were performed dishes were incubated at 30°C for 24 hours. To deter-
using MatGat (Campanella et al., 2003), and evolutio- mine the pigment produced by the reporter strains, the
nary relationships between AHL-lactonases were done length was measured and the reproducibility was deter-
using MEGA5 (Tamura et al., 2011). mined by 20 replicates.
The subcloning into the expression vector pCold IV
Statistical Analysis
(Takara- BIO-INC®), gene expression and protein purifi-
cation are described by Pedroza et al. (2014). Data was analyzed by using the ANOVA test. The con-
fident values were set at 95%.
Homology and phylogenetic dendrogram
of AHL-degrading enzyme Results
The similarity and identity analyses were performed
using MatGat (Campanella et al., 2003), and evolu-
B. thuringiensis AHL-inactivating activity
tionary relationships between AHL-lactonases were Inactivation of AHLs by B. thuringiensis strains is consi-
done using MEGA5 (Tamura et al., 2011). The evolu- dered effective when in a given evaluation period, the
tionary history was inferred using the Neighbor-Joining size of the colored area decreases with the time. When
Method (Saitou and Nei, 1987). The optimal tree with no color is observed at the first time of evaluation
the sum of branch length was = 0.34721705. The tree (30 min), the strain is listed as a candidate for in vitro
was drawn to scale, with branch lengths in the same pathogenicity inhibition assays. From the 310 B. thurin-
units as those of the evolutionary distances used to giensis strains isolated from phylloplane plants tested,
infer the phylogenetic tree. The evolutionary distances 251 showed AHL-lactonase activity with C6-HSL and
were computed using the Maximum Composite Likeli- C8-HSL; C6-HSL was degraded by 57% of the B. thurin-
hood Method (Tamura et al., 2004) and are in the units giensis strains, while C8-HSL was inactivated by 43% of
of the number of base substitutions per site. The analy- the B. thuringiensis strains. B. thuringiensis strains that
sis involved 22 nucleotide sequences. Codon positions
exhibit strong AHL lactonase activity against C6-HSL
included were 1st+2nd+3rd+Noncoding. All positions
and C8-HSL are shown in table 1. The screening to the-
containing gaps and missing data were eliminated.
There were a total of 570 positions in the final dataset. se strains using CV026 in are shown in figure 1. The
detectable concentration of the reporter strains was
between 100-120 µM of AHLs.
AHL-lactonase activity of recombinant E. coli DE3
The recombinant E. coli DE3 containing the expression Effect of B. thuringiensis cultures on soft rot
cassette pColdIV-AiiA was grown at 37°C in LB broth symptoms caused by P. caratovorum
with ampicillin (50 µg/ml) at 200 rpm. After 5 hours of
growth (O.D. 600 nm = 0.83), the IPTG (3.2 mM) was To test the attenuation of soft rot symptoms, B.
added and the incubation was continued overnight to thuringiensis strains displaying the highest AHL-lac-
reach an O.D. of 2.6 at 600 nm (Zhang et al., 2007). tonase activity according to the results with the bio-
The cell culture was divided in several fractions in order sensor strains were selected. The plant pathogen P.
to determine the AHL-lactonase activity. The first and caratovorum isolated from potato was used in these
second fractions were added each to LB medium in pre- assays and its pathogenicity was evaluated on pota-
sence of 100 µM of synthetic C8-HSL and C6-HSL, the to slices showing severe tissue maceration. When
third and fourth fractions were added to LB medium in potato slices were pretreated with B. thuringiensis
the presence of 100 µM of synthetic 3-O-C6-HSL and suspension (2x107 UFC/ml) before inoculation with
3-O-C12-HSL, respectively. The fifth fraction was co-ino- P. caratovorum, the soft rot symptoms were conside-
culated with 20 µl of a P. caratovorum culture (OD600 = rably less severe compared with the soft rot produ-
0.8) in 5 ml of LB media. All the fractions were incuba- ced on slices without previous treatment. According
ted at 37°C for 18 h at 200 rpm. The experiments inclu- to the evaluation scale of soft rot symptoms, the
ded B. thuringiensis 147-11516, as positive control and E. coli strain B. thuringiensis147-115-16 displayed the highest

156 Rev. Colomb. Biotecnol. Vol. XVI No. 1 Julio 2014 153-162
efficiency inhibiting P. caratovorum pathogenicity (rpsblast; http://www.ncbi.nlm.nih.gov/Structure/cdd/
(figure 2). wrpsb.cgi; domain COG0491GloB, Zn dependent
hydrolases, including glyoxylases (residues 78-250);
Cloning and sequence analysis of the AiiA gene domain pfam00753, the lactamase-β domain, meta-
llo-beta-lactamase superfamily (residues 33-235); and
B. thuringiensis147-11516 strain displayed the best results domain COG1237, metal dependent hydrolases do-
in the biosensor assays, as well as in the in vitro patho- main of the β lactamase superfamily (residues 22-161).
genicity assays; therefore, it was selected for molecu- Using MEME and MAST programs (Bailey and Gribskov,
lar characterization. The length of expected amplified 1998), in which protein sequences are analyzed for
PCR product containing the gene coding AiiA was similarities among hydrolases, three motifs were also
around 820 bp. Several clones that showed this length, found in B. thuringiensis 147-11516 AiiA: motif 1 (residues
exhibit a 754 bp ORF with sequence homology to aiiA 11-60); motif 2 (residues 76-125), and motif 3 (residues
genes reported in GenBank. The DNA sequence of B. 128-177). These motifs of the AiiA are also present in
thuringiensis 147-11516 gene was reported in GenBank the three Zn-dependent hydrolases.
with accession number EF379241. Comparison of the
B. thuringiensis147-11516 AiiA gene with other AiiA genes
Recombinant E. coli DE3- pCold-AiiA shown
revealed maximum identity in the nucleic acid sequen-
ce between 93% to 99%. The dendogram show that lactonase activity
aiiA gene of B. thuringiensis147-11516 is most similar to The lactonase activity of the recombinant E. coli DE3
B. thuringiensis subsp.aizawai and indiana (figure 3). was tested with synthetic lactones, C8-HSL and C6-HSL
At protein level three conserved domains in the pro- in the presence of the reporter strains CV026 and, with
tein aiiA of the B. thuringiensis147-11516 were detected 3-O-C6-HSL and 3-O-C12-HSL in the case of NTL4. The
by BLAST CD search of Conserved Domain Database results showed lack of purple pigmentation of strain

Figure 1. C. violaceum CVO26 with C6-HSL (HHL) as substrate. Well (+), reaction buffer with C6-HSL (20 µM); well (-), reaction
buffer only.

Table 1. AHL-lactonase activity of eight B. thuringiensis strains determined by biosensor strains. A: C. violaceum CVO26 with C6-HSL
as substrate. Well (+), reaction buffer with C6-HSL (20 µM); well (-), reaction buffer only.

Evaluation time
Well number Strain Phylloplane origin
30 min 60 min 120 min
1 147-11516 Phaseolus vulgaris +++ +++ +++
2 146-17202 Piper glanduligeron - - -
3 146-15505 Piper calceolarium - - -
4 147-0206 Zea mays + +++ +++
5 146-16312 Piper crassinervium + +++ +++
6 146-16702 Piper danielgonzalezi - +++ +++
7 146-15533 Piper calceolarium +++ +++ +++
8 147-12003 Zea mays +++ +++ +++

N-acyl homoserine lactonase (AiiA) from Bacillus thuringiensis 157

Figure 2. Attenuation of P. carotovorum pathogenicity by AHL-lactonase activity of B. thuringiensis. (E) Potato slice inoculated with P.
carotovorum alone, (E+Bt) potato slice pretrated with B. thuringiensis and inoculated with P. carotovorum, (Bt) potato slice pretrated
with B. thuringiensis suspension only. A. No control of P. carotovorum symptoms by strain B. thuringiensis 146-17202, B. Moderate control
of P. carotovorum symptoms by strain B. thuringiensis146-16702, C. Total control of P. carotovorum symptoms by strain B. thuringiensis147-11516.

CV026 (figure 4) and in the case of NTL4, exhibit lack breaking down AHL molecules that contain different
of blue pigmentation. In the presence of the pathogen acyl side chain lengths (Lee et al., 2002). In this study,
P. caratovorum, the QQ signals were disrupted (figure two synthetic AHLs with different acyl chain lengths, C6-
4A, lane 2 and 4B lane 1). HSL and C8-HSL, were inactivated by B. thuringiensis
147-11516 detected by the biosensor strains A. tumefaciens
In all the cases, disruption of QS by the recombinant E. NTL4 and C. violaceum CV026. The biosensor strain
coli DE3, is shown by the lack of pigmentation in the NTL4 showed blue color as response in the presence
presence of biosensor strains in comparison with the of AHLs produced by P. caratovorum. In the in vitro
control, with the pathogen alone, which exhibits pig- assays using pretreated potatoes slices with B. thurin-
ment production in response to both, long and short giensis 147-11516 cultures, attenuation of the soft rot symp-
chain lactones. ANOVA analysis showed statistically toms caused by P. caratovorum were observed, which
significant differences between lactones indicating could suggest an interference of the B. thuringiensis 147-
the preference to short chain than those that exhibit 11516 AiiA towards AHL signaling molecules produced
long-chain oxo substitutions. There was no statistical by P. caratovorum. This signaling molecules including
difference within the same group of lactones (figure 5). those that have been reported to P. caratovorum such
These results demonstrated the preference of recombi- as 3-oxo substitutions in the acyl chain (Chatterjee et
nant AiiA147-11516 for C8-HSL and C6-HSL. al., 2005), have been reported as a main regulators of
extracellular enzymes involved in potato infection and
Discussion responsible for symptoms development (Jones et al.,
1993; Pirhonen et al., 1993). The B. thuringiensis 147-11516
N-acyl homoserine lactones are signaling molecules
strain contains also the aiiA gene that encodes a AiiA
that are inactivated by the enzyme AHL-lactonase by
protein with a molecular weight of approximately 28,2
hydrolyzing the lactone ring, and in consequence, inhi-
kDa, which is similar to the predicted molecular mass
biting the virulence of gram negative pathogens such
of 28,036 Da of the protein reported by Dong et al.
as P. caratovorum (Dong et al., 2004). In this study,
(2000). The amino acid sequence alignments showed
the strain B. thuringiensis 147-11516 isolated from the phy-
identities of 90.8% to 99.6% to other AHL-lactonases
lloplane of Colombian plants, was found to display
described (Lee et al., 2002). The evolutionary distances
attenuation of P. caratovorum symptoms in potato
used to infer a phylogenetic tree confirm the wide dis-
bioassays.
tribution of aiiA homologous genes in B. thuringiensis
It has been established that the potential of some B. subspecies and individuals and with identities above
thuringiensis strains to attenuate infections depends on 93%. At protein level it was also observed the region

158 Rev. Colomb. Biotecnol. Vol. XVI No. 1 Julio 2014 153-162
Figure 3. Phylogenetic dendogram of AHL-degrading enzymes constructed using the neighbor-joining method. The bar indicates
1% estimated sequence divergence and the black circle highlight B. thuringiensis147-11516

Figure 4. A. Attenuation activity of AiiA using the reporter strain CVO26. Lane 1. Pathogen P. carotovorum; Lane 2: Recombinant
strain (DE3) co-inoculated with P. carotovorum; Lanes 3 and 4: wild type strain B. thuringiensis 147-11516 co-inoculated with P. carotovo-
rum; Controls: Lane 5: C6-HSL in the presence of CV026; Lane 6: C8-HSL in the presence of CV026 reporter strain. B. Attenuation
activity of AiiA using the reporter strain NTL4 in the presence of AHL. Lane 1. Recombinant strain DE3 co-inoculated with the
pathogen P. carotovorum; Lane 2: Recombinant strain (DE3); Lane 3: Recombinant strain DE3 in presence of 3-O-C12-HSL; Lane
4: Recombinant strain DE3 in the presence of 3-O-C6-HSL. Lane 5: Pathogen P. carotovorum grown alone; Lane 6: negative control
using the reporter strain alone without culture or extract added to the loading area.

N-acyl homoserine lactonase (AiiA) from Bacillus thuringiensis 159

 3-O-C12-HSL when they were tested with the biosen-
sor strain NTL4. These data indicates that lactonase
inactivation was not complete and that there was re-
maining lactones in the media (data not shown). It was
also observed the ability of recombinant E. coli DE3
strain to disrupt P. caratovorum communication when
they were co-inoculated in the presence of the repor-
ter strain. This attenuation suggests that the lactonase
produced by the recombinant strain exhibit activity to
modified lactones and interferes to signaling molecu-
les used by P. caratovorum.
The high homology and the presence of one conser-
ved motif 104HXHXDH109≈ H169 indicate that the AHL-lac-
tonase147-11516 belongs to the AHL-lactonase family. The
ability of the recombinant strain in P. caratovorum su-
Figure 5. Graphic obtained of the ANOVA (95%) analysis per- ggest an important role of AHL- lactonase to interfer the
formed from the data obtained on the activity essays. The AHLs signaling or AHLs response. Recently, we report
contrast between (a-b=-0.666667) and (c-d=-123.939) there the enzymatic hydrolysis from recombinant AiiA147-11516
are not shown significant difference. However, between (a- lactonase in order to determine its application (Pedro-
c=-10.397) (a-d= -116.364) (b-c=-97.303) and (b-d=-109.697) za et al., 2014). The activity to broad catalytic spec-
there are shown a significant difference. All data analysis trum of lactones including as N-butyryl-L-Homoserine
shown +/- Limits=2,278940. The lowest pigmentation means lactone (C4-HSL), N-heptanoyl-L-Homoserine lactone
highest activity. To C6-HSL and C8-HSL was obtained the (C7-HSL) and the enzymatic hydrolysis to C6-HSL in
greatest activity. To 3-O-C6-HSL and 3-O-C12-HSL was ob- alkaline pH, activity in high temperature (60°C) and
served larger pigmentation in the biosensor NTL4, the activi- decreasing of enzymatic activity by two metal ions, su-
ty among these AHLs was not significant. ggest that this enzyme is a promissory candidate for
the disease control programs by plants transformation.
Other escenarios such as the addition of enrichment
cultures of AHL degrading bacteria Bacillus sp. that in-
HLHFDH109≈ H169, that correspond to the motif 104HX-
104
crease the survival of aquaculture species (Tinh et al.,
HXDH109≈ H169 which is a complety conserved region 2008), the control over QS based bacterial biofilms in
among AiiA proteins. This motif contains a dinuclear biorefineries (Hong et al., 2012) and the incoporation
Zn2+ center in which the Zn1 is coordinated by H104, of QS inhibitors in medical and dental implants and
H106 and H169 while the Zn2 is coordinated by H109, catheters (Choudhary and Schmit-Dannert, 2010), pro-
H235, D108 and D191 (Kim et al., 2005). According to this vide further applications.
data, the AiiA from B. thuringiensis 147-11516 seems to be
metallo hydrolytic enzyme. The differences observed
Aknowledgments
between AiiA from B. thuringiensis 147-11516 (Pedroza et
al., 2014) and AHL- lactonaseBTK-AiiA (Kim et al., 2005) in The authors thank Dr. Clay Fuqua (Indiana Universi-
23 amino acids in which Ile-73 and Met-138 are part ty, Bloomington, Indiana) for providing C.violaceum
of hydrophobic channel and Tyr-165 and Ser-170 di- CVO26 and A. tumefaciens NTL4. We thank Dr. Oscar
ffer from the conserved region 165HTPGHTPGH173 invol- Alzate, for his critical review of the manuscript. This
ved in Zn coordination, could explain the capability work was supported by grants from The Colombian
of AiiA147-11516 to retain the activity in presence of high Department of Science, Technology and Innovation
concentrations of EDTA and increase three and four (2213-12-13773 and 1299-12-17827) to AMF.
times its activity to C4-HSL and C8-HSL respectively
(Pedroza et al., 2014). Bibliography
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