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Applied and Environmental Microbiology, July 2008, p. 4543-4549, Vol. 74, No. 14
0099-2240/08/$08.00+0 doi:10.1128/AEM.02041-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.
Coordinated Regulation of Cold-Induced Changes in Fatty Acids with Cardiolipin and Phosphatidylglycerol Composition among Phospholipid Species for the Food Pathogen Listeria monocytogenes
,
S. K. Mastronicolis,1*
N. Arvanitis,1
A. Karaliota,2
P. Magiatis,3
G. Heropoulos,4
C. Litos,2
H. Moustaka,1
A. Tsakirakis,1
E. Paramera,1 and
P. Papastavrou1
Food Chemistry Laboratory,1
Inorganic Chemistry Laboratory, Chemistry Department,2
Laboratory of Pharmacognosy and Natural Products Chemistry, Faculty of Pharmacy, University of Athens, Panepistimiopolis Zografou 15771, Athens, Greece,3
National Hellenic Research Foundation, Institute of Organic and Pharmaceutical Chemistry, 48 Vas. Constantinou Ave., Athens, Greece4
Received 6 September 2007/
Accepted 14 May 2008

ABSTRACT
We present here the structural identification of four phospholipid
(Phl) classes in
Listeria monocytogenes, the fatty acid (FA)
composition for each individual Phl species, and a description
of cold-induced FA changes. Cardiolipin (48.5%) and phosphatidylglycerol
(18.1%) are dominated by anteiso-FA, and the previously recognized
branched FA chain shortening by cold was observed singularly
in these Phls. Phosploaminolipid (19.9%) and phosphatidylinositol,
(9.1%) are significantly different, containing significant amounts
of straight-chain FA. These findings are supported by nuclear
magnetic resonance analysis.

INTRODUCTION
The bacterium
Listeria monocytogenes, one of the leading causes
of food-borne illness (
15), can adapt to cold and salinity (
9,
10,
31,
46,
53) and can survive even on dust or flakes of organic
material (
34).
Listeria is characterized by >85% branched-chain
fatty acids (FA), anteiso-15:0 (a-15:0) and anteiso-17:0 (a-17:0).
Cells grown in the cold (5°C) contain significantly less
a-17:0 than those grown at higher temperatures (
4,
8,
37,
43,
44,
57). A cryotolerance element of
Listeria is also its ability
to use cryoprotectant osmolytes (
31), a property shared by other
organisms (
2,
3,
12,
21,
23). The critical role of odd numbered
anteiso-FA in influencing the lower-temperature growth limits
has recently been reported (
14,
19,
25). We have reported previously
(
39) that
Listeria spp. can be cold adapted by an increased
content (30%) of neutral lipids (NL) among total lipids (TL)
and an increase in the a-15:0/a-17:0 FA ratio (FAr) of TL, polar
lipids (PL), and NL (10-, 10-, and 7-fold, respectively), as
well as by an increase in FAr (
38) for each NL subclasses 1,2-diglyceride,
1,3-diglyceride and free FA (6-, 5-, and 8-fold, respectively).
This study is a continuation (35, 36) of an investigation for the structural characterization of the major phospholipid (Phl) classes of L. monocytogenes, in order to (i) elucidate the isolation and quantification of each of class (cells at 30°C), (ii) evaluate the cold temperature (5°C) effect on each individual Phl class FA composition, and (iii) confirm the findings by 1H-nuclear magnetic resonance (NMR) analysis.
An avirulent strain of L. monocytogenes, DP-L1044 (D. Portnoy, University of Pennsylvania), prepared by a transposon insertion (6) in the parent strain (Lm10403S), was grown in brain heart infusion (Difco Laboratories) broth at 30°C (ca. 24 h). A 10-ml portion of this was then inoculated in 1 liter of brain heart infusion broth, followed by incubation until stationary phase (30 or 5°C). Cells pelleted by centrifugation were washed twice in phosphate buffer (pH 7.0). TL were extracted (17) and separated to PL and NL by solid-phase extraction (SPE) as previously described (38). Solvent A (chloroform-methanol-acetic acid-water [50:25:6:2,vol/vol/vol/vol]) was used for one-dimensionalal thin-layer chromatography (1D-TLC; silica gel G60 aluminum chromatoplate [Merck 1.05554], 0.25-mm thick, 10 by 10 cm). Spots were visualized by using iodine, ninhydrin, phosphomolybdenum blue (13), and copper sulfate (5, 42). Glyco- or sulfolipids were tested by using naphtholsulfuric acid (24). The standards phosphatidic acid (PA), phosphatidylserine (PS), cardiolipin (CL), phosphatidylglycerol (PG), phosphatidylethanolamine (PE), phosphatidylcholine (PC), phosphatidylinositol (PI), Lyso-PC, and Lyso-PE were purchased from Sigma Chemical Co. Each culture 30°C or 5°C PL sample (85 and 50 µg of phosphorus correspondingly) was fractionated by 1D-TLC (preparative), along with the standards (CL, PG, and PI) and along with another Listeria PL sample (30°C) aliquot (3.5 µg of phosphorus) as an alternative standard. Four individual Phl bands were separated, scraped off, and eluted from silica gel as previously described (35, 39). Each extracted band of residual lipids was used for analytical methods and 1H-NMR spectroscopy.
Total phosphorus (33), esters (47), nitrogen (20), and glycerol (30) analysis was performed as described previously. Deacylation (27, 54) was also performed in 0.1 ml of NaOH (1.2 N) in 50% (vol/vol) methanol at 45°C for 20 min. The PL in bulk were quantitated by weight after SPE column elution. Each individual Phl band (cells 30°C) was quantified after 1D-TLC fractionation of the PL sample (
10 µg of phosphorus) with solvent A (n = 10). Each iodine-visualized band was scraped into a digestion tube, and the total phosphorus content was determined (27). A 25-µg phosphorus sample of the TLC-extracted CL band (cells of 30°C) was dry acid methanolysed (51) by 400 µl of 3 N methanolic HCl, and the molecular ratios (structural data) were determined in hydrolysis aliquots as described previously (28).
For each culture CL, PG, phosphoaminolipids (PhAL), and PI FA were methylated by scraping the 1D-TLC bands into digestion tubes, and a 1-mg PL sample was also methylated as previously described (28, 35). FA methyl esters were separated by using a Hewlett-Packard 6890 gas chromatograph with split/splitless injector, flame ionization detector (30 m by 0.251 mm, capillary column DB-5ms; J&W Scientific). The carrier gas was He. The injector and detector were maintained at 250 and 280°C, respectively. The oven temperature was ramped from 90 to 170°C (70°C/min) and from 170 to 210°C (5°C/min). The initial and final holding times were 1 and 2 min, respectively. Two standards were used: bacterial FA methyl esters (CP Matreya, Inc.) and marine oil fame (Restek Corp.). Each lipid sample was analyzed by gas chromatography-mass spectrometry (electron impact or chemical ionization with acetonitrile) using a Varian Saturn 2000 with a 30-m-by-0.25-mm DB5-ms column. To each sample of CL (750 µg), PG (270 µg), PhAL (270 µg), and PI (150 µg) 0.5 ml of CDCl3/CD3OD (1:2 [vol/vol]) was added, and 1H-NMR spectra were acquired by using a Varian Unity Plus spectrometer (300 MHz). As standards, CL (1,000 µg), PG (540 µg), and PI (920 µg) were also analyzed.
L. monocytogenes TL extraction (at 30 or 5°C) yielded 5.2 ± 1.2 mg g–1 and 6.5 ± 1.4 mg g–1 wet cells. The TL lipid phosphorus and nitrogen contents were 3.4% ± 0.2% (30°C) and 2.5% ± 0.1% (5°C) and 0.96% ± 0.02% and 0.86% ± 0.02%, respectively. The PL for each culture represented 62.5% ± 2.3% and 53.3% ± 1.1%, respectively, of the TL. PL were separated by 1D-TLC into four phosphocomponents (see Fig. S1 in the supplemental material) designated g, f, e, and b, as we have previously described (36) for Listeria (30°C). Two bands, f and b, were cochromatographed with PG and PI standards, respectively. The component f includes (after 2D-TLC separation) two phosphocomponents, f2 and f3, but not the glycocomponent f1 (35). The component g was cochromatographed close to the CL standard. The ninhydrin-positive phosphocomponent e (migrated just below the PG position) is the single PhAL of Listeria (35, 36), as others (16) have also reported, and a lysylcardiolipin structure is suggested. This molecule can serve as a genus-specific chemotaxonomic marker for the genus Listeria. Table 1 shows the lipid phosphorus distribution of each lipid component (cells at 30°C). Of note is that the ratio of relative amounts at phosphorus percentages for CL/PhAL (
2.4) are similar to that (
2.8) reported by Fischer and Leopold (16). The existence of CL and PG has been reported by others (16, 32). Until now there has been no precedent in the literature for the existence of PI in Listeria PL.
Based on their TLC behavior before and after deacylation, the
four phosphocomponents of each culture PL sample were completely
hydrolyzed, and the bulk of the lipid phosphorus was distributed
in the water-soluble products. This suggests a basic glycerolipid
structure for each phosphocomponent. The hydrolysis products
after dry acid methanolysis of the phosphocomponent g, contained
total phosphorus, (methyl) esters, and glycerol at a molar ratio
of 2.00:4.00:3.12, respectively, and this suggests a diphosphatidylglycerol
(cardiolipin) molecular structure.
The four isolated glycerolipid components were also identified by 1H-NMR analysis (Tables 2 and 3). For each lipid class, the spectral assignments were compared to standard spectra of CL, PI, and PG (1, 7, 48). Diagnostic resonances may be considered to be the CL resonances of the central glycerol head group, sandwiched between two phosphate groups (OPCH2CHOHCH2OP) (Table 3 and Fig. 1) and, in principle, the PG resonances of its glycerol head group C4H2C5HC6H2 (Table 3 and Fig. 2). The PI head group is complicated because it represents a network of six interacting spins corresponding to the six inositol CH protons (see Fig. S3 in the supplemental material). The three features distinguishing PI are the C-4(POCH), C-6(CHOH), and C-7(CHOH) proton resonances (Table 3). The C-8(CHOH) signal at 3.200 ppm is overlapped by the methanol resonance. C-5 has the same peak (4.341ppm) as glycerol backbone C-1 (1, 7). The PhAL head group is suggested to be the same as the CL headgroup, with an esterified lysine moiety at the central free OH group. The methylene protons neighboring the
-amino group of lysine (CH2NH2) occur at 3.001 ppm. The central glycerol sandwiched between two phosphate groups could also be used as a diagnostic for this lipid (see Fig. S2 in the supplemental material) as for the CL structure described above.
This study represents the individual isolated Phl species (CL,
PG, PhAL, and PI) FA composition of
Listeria (30°C). FA
profiles of CL and PG are very similar and dominated by anteiso-FA.
The PhAL and PI FA compositions are significantly different,
containing significant amounts of straight-chain FA (16:0 and
18:0) and unsaturated FA (Table
4).
View this table:
[in this window]
[in a new window]
|
TABLE 4. Cold temperature dependence of FA composition (wt %) of CL, PG, PhAL, and PI from two sets of L. monocytogenes cultures at 30 and 5°Ca
|
Upon cold stress the a-15:0 FA proportion in their CL and PG
of
Listeria increased dramatically (Table
4). The main cold
change for PhAL FA was, apart from the increase of anteiso-15:0,
the decrease of the sum of unsaturated FA. Cold differences
between the FA composition of PI species (unpublished data)
were mainly independent of the growth temperature (the differences
varied between ±4.0 percentage points, with the exception
of a 15:0 FA, which showed a difference of +6.2). Conclusively,
the cold metabolic change in CL and PG is different from the
rest of the PL subclasses (PI and PhAL). The cold decrease of
the -CH
2-/-CH
3 ratio of the acyl chains by NMR analysis (Table
5 and Fig.
3) reflects the cold increase of the branched-15:0/branched-17:0
FA ratio (as determined by gas chromatography analysis) for
CL and PG, as well as for PhAL (Table
4). The determination
of branched FA by
1H-NMR analysis can be a useful interpretation
tool of FA microorganism metabolism at cold temperature.
View this table:
[in this window]
[in a new window]
|
TABLE 5. Temperature dependence of the -CH2-/-CH3 ratio of CL, PG, and PhAL FA chains from cells of L. monocytogenes grown at 30 and 5°Ca
|
The potential impacts of studying
L. monocytogenes membrane
Phl composition are that (i) molecules can serve as a chemotaxonomic
marker, (ii) resistance to antimicrobials and nisin (
11,
40,
41,
52,
56) or other antimicrobial peptides (
49,
50) is correlated
with both altered FA composition (
26) and Phl compositional
changes, (iii) antibacterials encapsulated in liposomes produced
with PhL of similar structure as that included in
Listeria membrane
are more effective (improved permeation) (
55), (iv) an understanding
of the cold stress response ia helpful in the design of effective
food preservation strategies (such as membrane-disrupting techniques
like pulsed electric fields, ultrahigh pressure, etc.) applicable
to hurdle technology, etc. (
45), and (v) FA biosynthesis is
coordinately regulated with Phl synthesis and growth as part
of the bacteria response to the changing environment and offers
unique sites for selective inhibition (
22) to combat microbial
infection (chemotherapeutic agents). Phl FA fingerprints help
us to monitor the impact on bacterial growth conditions (
18).

ACKNOWLEDGMENTS
This research was supported in part by the Special Research
Account of National and Kapodistrian University of Athens under
project no. 70/4/3338.

FOOTNOTES
* Corresponding author. Mailing address: Food Chemistry Laboratory, Department of Chemistry, Panepistimiopolis Zografou 15771, Athens, Greece. Phone: 30 210 7274326. Fax: 30 210 7274476. E-mail:
smastro{at}chem.uoa.gr 
Published ahead of print on 23 May 2008. 
Supplemental material for this article may be found at http://aem.asm.org/. 

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Applied and Environmental Microbiology, July 2008, p. 4543-4549, Vol. 74, No. 14
0099-2240/08/$08.00+0 doi:10.1128/AEM.02041-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.