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Applied and Environmental Microbiology, August 2008, p. 4764-4767, Vol. 74, No. 15
0099-2240/08/$08.00+0 doi:10.1128/AEM.00078-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.
Variations in the Degree of D-Alanylation of Teichoic Acids in Lactococcus lactis Alter Resistance to Cationic Antimicrobials but Have No Effect on Bacterial Surface Hydrophobicity and Charge
Efstathios Giaouris,1,2,
Romain Briandet,2
Mickael Meyrand,1
Pascal Courtin,1 and
Marie-Pierre Chapot-Chartier1*
INRA, UR477 Biochimie Bactérienne, F-78350 Jouy-en-Josas, France,1
INRA-AgroParisTech, UMR 763 Bioadhesion et Hygiène des Matériaux, 25 avenue de la République, F-91300 Massy, France2
Received 10 January 2008/
Accepted 29 May 2008

ABSTRACT
An increase of the degree of
D-alanylation of teichoic acids
in
Lactococcus lactis resulted in a significant increase of
bacterial resistance toward the cationic antimicrobials nisin
and lysozyme, whereas the absence of
D-alanylation led to a
decreased resistance toward the same compounds. In contrast,
the same variations of the
D-alanylation degree did not modify
bacterial cell surface charge and hydrophobicity. Bacterial
adhesion to polystyrene and glass surfaces was not modified
either.

INTRODUCTION
The gram-positive cell wall is formed by a thick peptidoglycan
layer decorated with proteins, polysaccharides, and mainly polymers
of alternating phosphate and alditol groups called teichoic
acids (
5). Teichoic acids are either covalently linked to the
peptidoglycan (wall teichoic acids) or anchored to the membrane
through a glycolipid (lipoteichoic acids [LTAs]) (
20). In many
gram-positive bacteria, the products of the
dlt operon genes
are involved in
D-alanylation of teichoic acids (
20,
24). Mutants
with teichoic acids lacking
D-alanine esters have been shown
to exhibit a variety of phenotypic changes, especially altered
resistance to cationic antimicrobials (
13,
15,
23,
25) and modified
adhesion and biofilm formation (
1,
8,
10,
30).
Lactococcus lactis is widely used in dairy fermentations and also serves as a model organism for biological studies of lactic acid bacteria. In L. lactis, the characterization of dlt mutants has revealed the role of teichoic acid D-alanylation in UV sensitivity, autolysis, and protein secretion (7, 21, 27). The aim of this study was to examine the impact of D-alanylation of L. lactis teichoic acids on resistance to cationic antimicrobials and, in parallel, on the physicochemical properties of the bacterial surface and on bacterial adhesion to solid surfaces.

Overexpression of the dlt operon and D-alanine quantification of teichoic acids.
The genetic organization of the
dlt operon in
L. lactis MG1363
is depicted in Fig.
1. To overproduce the
dlt genes in
L. lactis,
we used the nisin-controlled expression system (
16). The
dlt operon was placed under the control of the
nisA promoter (
6).
For this, a 4,274-bp fragment encompassing the complete
dlt operon and starting at the ATG codon of
dltA was amplified by
PCR using primers U-DLT-NcoI (CATG
CCATGGGAAAATTATTAGACAAATTTTTG
[NcoI site underlined]) and
L-DLT-KpnI (GG
GGTACCTTATTTTAAGACAGACTCTG
[KpnI site underlined]), with MG1363 DNA as the template and
with TripleMaster
Taq polymerase (Eppendorf). The PCR product
was cloned downstream of the
nisA promoter into the pNZ8048
plasmid (obtained from NIZO, The Netherlands Institute for Dairy
Research, Ede, The Netherlands) (
14), yielding plasmid pNZ
dlt.
The recombinant plasmid was used to transform
L. lactis NZ9000,
a derivative of MG1363 with
nisRK genes integrated into its
chromosome, by electroporation (Table
1). In this host, nisin
can activate the
nisA promoter via signal transduction mediated
by a two-component regulatory system composed of histidine kinase
NisK and response regulator NisR (
16).
The amount of
dlt transcript in strain NZ9000(pNZ
dlt) after
induction with nisin (1 ng/ml) (Sigma) was measured by real
time reverse transcription-PCR. RNA extraction and cDNA synthesis
were performed as described previously (
12). Primers (GTTCTCGGTTCGTCAGAAATGG
and TAATGTCGTTGTTCCGGGTTG) located inside the
dltD gene were
designed using Primer Express software from Applied Biosystems.
Real-time PCR was carried out using Sybr green PCR master mix
(Applied Biosystems) as recommended by the supplier. Reactions
were run in duplicates with a Mastercycler ep realplex instrument
(Eppendorf). The cycle threshold was used to determine the relative
dltD gene expression levels. Data were computed using the comparative
critical threshold (2
–
CT) method. The results were normalized
with the
L. lactis tuf gene, encoding the elongation factor
TU, as a control as described previously (
26). The results indicated
a 50-fold increase of the amount of
dlt transcript in the NZ9000(pNZ
dlt)
strain compared to the levels for the control strain NZ9000(pNZ)
after nisin induction.
The amount of D-alanine esterified to teichoic acids was measured for the overexpressing strain NZ9000(pNZdlt) as well as for the dltD-negative mutant MG1363dltD, obtained previously by Duwat et al. (7). Bacteria were grown overnight at 30°C in M17-glucose broth supplemented with chloramphenicol (5 µg/ml) and nisin (1 ng/ml) for NZ9000(pNZdlt) and the control strain NZ9000(pNZ). D-Alanine was released from whole cells by alkaline hydrolysis, as reported previously for Streptococcus pneumoniae (13) and group A Streptococcus (15), and quantified by high-performance liquid chromatography after derivatization with Marfey's reagent (1-fluoro-2,4-dinitrophenyl-5-L-alanine amide; Sigma) (28). The results showed that a larger amount of D-alanine was released from the dlt overexpressing strain NZ9000(pNZdlt) than from the control strain NZ9000(pNZ) (1.5-fold-larger amount) (Fig. 2). On the other hand, almost no D-alanine was released from the dltD mutant. The lack of D-alanylation in dlt mutants of a number of gram-positive pathogens has also been reported (1, 8, 15, 25).

Sensitivity to cationic antimicrobials.
In the absence of
D-alanine substitutions, teichoic acids are
expected to bear higher negative charges, since the positively
charged amino groups of
D-alanyl esters partially counteract
the negative charges of the backbone phosphate groups (
20).
In several bacterial species,
dlt-deficient mutants have been
found to be more sensitive to cationic antimicrobials (
13,
15,
23,
25). In this study, the MICs for nisin and lysozyme (pI
values of nisin and lysozyme, 10.5 and 11.35, respectively)
were determined for the four strains, using the optical density
modeling method which was described by Guillier et al. (
11).
The strains NZ9000(pNZ
dlt) and NZ9000(pNZ) were precultured
twice in the presence of chloramphenicol. Then, bacterial growth
was monitored in medium without chloramphenicol, using a Bioscreen
C apparatus with microtiter plates, in the presence of 10 different
concentrations of each antimicrobial. Afterwards, growth rate
was estimated by fitting the data to the modified Gompertz model
(
2) and a dose response curve was obtained by using the Lambert-Pearson
model (
17), leading to MIC determination. The MIC of nisin for
the
dltD-negative mutant was reduced compared to that for MG1363,
as previously reported by Kramer et al. (
14), which confirms
the involvement of teichoic acid
D-alanylation in nisin resistance
in
L. lactis (Fig.
3A). Similarly, the MIC of lysozyme for the
dlt-deficient mutant was greatly reduced compared to that for
MG1363 (Fig.
3B). In contrast, the
dlt-overexpressing strain
NZ9000(pNZ
dlt) was more resistant to both nisin and lysozyme
than the control strain NZ9000(pNZ) as well as the wild-type
strain MG1363 (Fig.
3A and B).

Surface physicochemical properties and adhesion to solid surfaces.
In several previous studies,
D-alanine deprivation of teichoic
acids was hypothesized to result in a more negative cell surface
(
10,
15,
22). Besides, LTA is recognized as a main determinant
of cell surface hydrophobicity (
19). However, in these studies,
the bacterial surface properties were not investigated with
physicochemical methods. In our study, first we examined the
hydrophobic/hydrophilic cell surface properties of the
dlt mutant
strains and their Lewis acid-base characteristics with the microbial-adhesion-to-solvents
method, described by Bellon-Fontaine et al. (
3). Strains were
compared for their affinities to two pairs of solvents: hexadecane-chloroform
and decane-ethyl acetate. The results for the microbial-adhesion-to-solvents
method did not reveal any significant differences between the
dltD mutant, the overexpressing strain, and the wild-type or
the control strain as regards their surface hydrophobicities
and polarities (data not shown). Low affinity to apolar solvents
(decane and hexadecane) (around 10%) revealed the hydrophilic
character of the surface of MG1363 as well as the three other
strains. Second, the electrical properties of the bacterial
surface were assessed by electrophoretic mobility measurements,
as previously described (
4). Surprisingly, no significant differences
at the overall net surface charge were observed between the
dlt mutant and MG1363 or between the overexpressing strain and
the control strain (Fig.
4). These data reveal that the variations
of the degree of
D-alanine substitution of
L. lactis teichoic
acids, at least in the range tested in this study, do not modify
the global bacterial surface charge.
Furthermore, we examined whether the altered
D-Ala content of
teichoic acids could influence
L. lactis interactions with solid
surfaces. We tested the adhesion of bacteria to polystyrene
microtiter plates by using the method described by van Merode
et al. (
29) and also to glass slides (25 by 25 mm) by quantifying
the number of attached cells through acridine orange staining
and epifluorescence microscopy, as previously described (
18).
No significant differences in adhesion to hydrophobic polystyrene
and hydrophilic glass were observed between the strains (data
not shown). This result correlates with the absence of differences
in cell surface physicochemical properties between the different
strains tested.
In sum, the present results show a correlation between the degree of D-alanylation of teichoic acids in L. lactis and the resistance to cationic antimicrobials, in agreement with the data obtained for several other gram-positive bacterial species (13, 15, 23, 25). However, no modification of the bacterial surface physicochemical properties was observed in relation to the teichoic acid D-alanylation degree in the range tested. In L. lactis MG1363, the ratio of D-Ala to glycerol-phosphate (GroP) on LTA was estimated to be 28.5% (27). Taking into account this value and the results of D-Ala quantification shown on Fig. 2, we can estimate that the D-Ala/GroP ratios in LTAs of the tested strains ranged from 4% to 45%. The electronegative and hydrophilic characters of the surfaces of MG1363 and its derivative strains suggest that wall teichoic acids and/or LTAs are exposed at the cell surface and responsible for the global negative charge. However, the fact that the D-alanylation level does not modify the surface global charge suggests that, in L. lactis, the D-alanyl substituents of teichoic acids are located inside the cell wall rather than exposed at the cell surface. Nisin and lysozyme are small molecules that can diffuse inside the cell wall to exert their inhibitory activity, in the case of nisin at the level of the cytoplasmic membrane through lipid II binding (31). The D-Ala substituents on teichoic acids located inside the cell wall could reduce the accumulation of these cationic antimicrobials inside the cell wall and in the vicinity of the cytoplasmic membrane and thus could increase the bacterial resistance to these molecules.

ACKNOWLEDGMENTS
E.G. was a recipient of a Marie Curie Fellowship for Early Stage
Research Training (EST) of the LABHEALTH Project (MEST-CT-2004-514428).
We are very grateful to A. Gruss (INRA, UBLO, Jouy-en-Josas, France) for providing us with the L. lactis MG1363dltD mutant strain. We warmly thank Margareth Renault and Florence Dubois-Brissonnet (UMR-BHM, AgroParisTech-INRA, Massy, France) for their precious help with MIC determination.

FOOTNOTES
* Corresponding author. Mailing address: INRA, Unité de Biochimie Bactérienne, Domaine de Vilvert, 78352 Jouy-en-Josas Cedex, France. Phone: 33 1 34 65 22 68. Fax: 33 1 34 65 21 63. E-mail:
Marie-Pierre.Chapot{at}jouy.inra.fr 
Published ahead of print on 6 June 2008. 
Present address: Laboratory of Microbiology and Biotechnology of Foods, Department of Food Science and Technology, Agricultural University of Athens, Athens, Greece. 

REFERENCES
1 - Abachin, E., C. Poyart, E. Pellegrini, E. Milohanic, F. Fiedler, P. Berche, and P. Trieu-Cuot. 2002. Formation of D-alanyl-lipoteichoic acid is required for adhesion and virulence of Listeria monocytogenes. Mol. Microbiol. 43:1-14.[CrossRef][Medline]
2 - Augustin, J. C., L. Rosso, and V. Carlier. 1999. Estimation of temperature dependent growth rate and lag time of Listeria monocytogenes by optical density measurements. J. Microbiol. Methods 38:137-146.[CrossRef][Medline]
3 - Bellon-Fontaine, M.-N., J. Rault, and C. J. van Oss. 1996. Microbial adhesion to solvents: a novel method to determine the electron donor/electron acceptor or Lewis acid-base properties of microbial cells. Colloids Surf. B 7:47-53.[CrossRef]
4 - Briandet, R., T. Meylheuc, C. Maher, and M. N. Bellon-Fontaine. 1999. Listeria monocytogenes Scott A: cell surface charge, hydrophobicity, and electron donor and acceptor characteristics under different environmental growth conditions. Appl. Environ. Microbiol. 65:5328-5333.[Abstract/Free Full Text]
5 - Delcour, J., T. Ferain, M. Deghorain, E. Palumbo, and P. Hols. 1999. The biosynthesis and functionality of the cell-wall of lactic acid bacteria. Antonie van Leeuwenhoek 76:159-184.[CrossRef][Medline]
6 - de Ruyter, P. G., O. P. Kuipers, and W. M. de Vos. 1996. Controlled gene expression systems for Lactococcus lactis with the food-grade inducer nisin. Appl. Environ. Microbiol. 62:3662-3667.[Abstract]
7 - Duwat, P., A. Cochu, S. D. Ehrlich, and A. Gruss. 1997. Characterization of Lactococcus lactis UV-sensitive mutants obtained by ISS1 transposition. J. Bacteriol. 179:4473-4479.[Abstract/Free Full Text]
8 - Fabretti, F., C. Theilacker, L. Baldassarri, Z. Kaczynski, A. Kropec, O. Holst, and J. Huebner. 2006. Alanine esters of enterococcal lipoteichoic acid play a role in biofilm formation and resistance to antimicrobial peptides. Infect. Immun. 74:4164-4171.[Abstract/Free Full Text]
9 - Gasson, M. J. 1983. Plasmid complements of Streptococcus lactis NCDO 712 and other lactic streptococci after protoplast-induced curing. J. Bacteriol. 154:1-9.[Abstract/Free Full Text]
10 - Gross, M., S. E. Cramton, F. Gotz, and A. Peschel. 2001. Key role of teichoic acid net charge in Staphylococcus aureus colonization of artificial surfaces. Infect. Immun. 69:3423-3426.[Abstract/Free Full Text]
11 - Guillier, L., A. I. Nazer, and F. Dubois-Brissonnet. 2007. Growth response of Salmonella typhimurium in the presence of natural and synthetic antimicrobials: estimation of MICs from three different models. J. Food Prot. 70:2243-2250.[Medline]
12 - Ibrahim, M., A. Guillot, F. Wessner, F. Algaron, C. Besset, P. Courtin, R. Gardan, and V. Monnet. 2007. Control of the transcription of a short gene encoding a cyclic peptide in Streptococcus thermophilus: a new quorum-sensing system? J. Bacteriol. 189:8844-8854.[Abstract/Free Full Text]
13 - Kovács, M., A. Halfmann, I. Fedtke, M. Heintz, A. Peschel, W. Vollmer, R. Hakenbeck, and R. Bruckner. 2006. A functional dlt operon, encoding proteins required for incorporation of D-alanine in teichoic acids in gram-positive bacteria, confers resistance to cationic antimicrobial peptides in Streptococcus pneumoniae. J. Bacteriol. 188:5797-5805.[Abstract/Free Full Text]
14 - Kramer, N. E., S. A. van Hijum, J. Knol, J. Kok, and O. P. Kuipers. 2006. Transcriptome analysis reveals mechanisms by which Lactococcus lactis acquires nisin resistance. Antimicrob. Agents Chemother. 50:1753-1761.[Abstract/Free Full Text]
15 - Kristian, S. A., V. Datta, C. Weidenmaier, R. Kansal, I. Fedtke, A. Peschel, R. L. Gallo, and V. Nizet. 2005. D-Alanylation of teichoic acids promotes group a streptococcus antimicrobial peptide resistance, neutrophil survival, and epithelial cell invasion. J. Bacteriol. 187:6719-6725.[Abstract/Free Full Text]
16 - Kuipers, O. P., P. G. G. de Ruyter, M. Kleerebezem, and W. M. de Vos. 1998. Quorum sensing-controlled gene expression in lactic acid bacteria. J. Biotechnol. 64:15-21.[CrossRef]
17 - Lambert, R. J., and R. Lambert. 2003. A model for the efficacy of combined inhibitors. J. Appl. Microbiol. 95:734-743.[CrossRef][Medline]
18 - Mercier, C., C. Durrieu, R. Briandet, E. Domakova, J. Tremblay, G. Buist, and S. Kulakauskas. 2002. Positive role of peptidoglycan breaks in lactococcal biofilm formation. Mol. Microbiol. 46:235-243.[CrossRef][Medline]
19 - Miörner, H., G. Johansson, and G. Kronvall. 1983. Lipoteichoic acid is the major cell wall component responsible for surface hydrophobicity of group A streptococci. Infect. Immun. 39:336-343.[Abstract/Free Full Text]
20 - Neuhaus, F. C., and J. Baddiley. 2003. A continuum of anionic charge: structures and functions of D-alanyl-teichoic acids in gram-positive bacteria. Microbiol. Mol. Biol. Rev. 67:686-723.[Abstract/Free Full Text]
21 - Nouaille, S., J. Commissaire, J. J. Gratadoux, P. Ravn, A. Bolotin, A. Gruss, Y. Le Loir, and P. Langella. 2004. Influence of lipoteichoic acid D-alanylation on protein secretion in Lactococcus lactis as revealed by random mutagenesis. Appl. Environ. Microbiol. 70:1600-1607.[Abstract/Free Full Text]
22 - Palumbo, E., M. Deghorain, P. S. Cocconcelli, M. Kleerebezem, A. Geyer, T. Hartung, S. Morath, and P. Hols. 2006. D-Alanyl ester depletion of teichoic acids in Lactobacillus plantarum results in a major modification of lipoteichoic acid composition and cell wall perforations at the septum mediated by the Acm2 autolysin. J. Bacteriol. 188:3709-3715.[Abstract/Free Full Text]
23 - Perea Vélez, M., T. L. Verhoeven, C. Draing, S. Von Aulock, M. Pfitzenmaier, A. Geyer, I. Lambrichts, C. Grangette, B. Pot, J. Vanderleyden, and S. C. De Keersmaecker. 2007. Functional analysis of D-alanylation of lipoteichoic acid in the probiotic strain Lactobacillus rhamnosus GG. Appl. Environ. Microbiol. 73:3595-3604.[Abstract/Free Full Text]
24 - Perego, M., P. Glaser, A. Minutello, M. A. Strauch, K. Leopold, and W. Fischer. 1995. Incorporation of D-alanine into lipoteichoic acid and wall teichoic acid in Bacillus subtilis. Identification of genes and regulation. J. Biol. Chem. 270:15598-15606.[Abstract/Free Full Text]
25 - Peschel, A., M. Otto, R. W. Jack, H. Kalbacher, G. Jung, and F. Gotz. 1999. Inactivation of the dlt operon in Staphylococcus aureus confers sensitivity to defensins, protegrins, and other antimicrobial peptides. J. Biol. Chem. 274:8405-8410.[Abstract/Free Full Text]
26 - Sperandio, B., P. Polard, D. S. Ehrlich, P. Renault, and E. Guedon. 2005. Sulfur amino acid metabolism and its control in Lactococcus lactis IL1403. J. Bacteriol. 187:3762-3778.[Abstract/Free Full Text]
27 - Steen, A., E. Palumbo, M. Deghorain, P. S. Cocconcelli, J. Delcour, O. P. Kuipers, J. Kok, G. Buist, and P. Hols. 2005. Autolysis of Lactococcus lactis is increased upon D-alanine depletion of peptidoglycan and lipoteichoic acids. J. Bacteriol. 187:114-124.[Abstract/Free Full Text]
28 - Szokan, G., G. Mezo, and F. Hudecz. 1988. Application of Marfey's reagent in racemization studies of amino acids and peptides. J. Chromatogr. 444:115-122.[CrossRef][Medline]
29 - van Merode, A. E., H. C. van der Mei, H. J. Busscher, and B. P. Krom. 2006. Influence of culture heterogeneity in cell surface charge on adhesion and biofilm formation by Enterococcus faecalis. J. Bacteriol. 188:2421-2426.[Abstract/Free Full Text]
30 - Walter, J., D. M. Loach, M. Alqumber, C. Rockel, C. Hermann, M. Pfitzenmaier, and G. W. Tannock. 2007. D-Alanyl ester depletion of teichoic acids in Lactobacillus reuteri 100-23 results in impaired colonization of the mouse gastrointestinal tract. Environ. Microbiol. 9:1750-1760.[CrossRef][Medline]
31 - Wiedemann, I., E. Breukink, C. van Kraaij, O. P. Kuipers, G. Bierbaum, B. de Kruijff, and H. G. Sahl. 2001. Specific binding of nisin to the peptidoglycan precursor lipid II combines pore formation and inhibition of cell wall biosynthesis for potent antibiotic activity. J. Biol. Chem. 276:1772-1779.[Abstract/Free Full Text]
Applied and Environmental Microbiology, August 2008, p. 4764-4767, Vol. 74, No. 15
0099-2240/08/$08.00+0 doi:10.1128/AEM.00078-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.
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