BMC Biotechnology 2006, 6:2 http://www.biomedcentral.com/1472-6750/6/2
Page 10 of 11
(page number not for citation purposes)
Plasmid constructions
Plasmids were constructed using standard molecular clon-
ing and PCR fusion (overlap extension) techniques [21].
Primers were purchased from Invitrogen Life Technolo-
gies (São Paulo, Brazil) and Integrated DNA Technologies,
Inc. (Coralville, IA, USA), and are listed in Table 1. Plas-
mid pLBS-GFP-Em
R
(Fig. 3) was designed to contain the
'backbone' elements of the cloning vector pCR2.1-Topo:
the replication determinants (pUC ori), and ampicillin
and kanamycin resistance markers for E. coli. The Lactoba-
cillus specific sequences were PCR amplified from
genomic DNA of L. crispatus strain F5.7 to assemble the
expression cassette containing the lbs promoter, leader
peptide, anchor and terminator sequences. Homologous
sequences to the anchor region of Lbs are found in other
S-layer proteins from different Lactobacillus species, such
as Slp of L. acidophilus (accession X89375, X89376), SlpH
of L. helveticus (accession X91199, X92752), Lgs of L. gall-
inarum (accession AY597259, AY597266), Slp of L. sunto-
ryeus (accession AY641395), Cbs of L. crispatus (accession
AF001313, AF079365), with nucleotide identities higher
than 80% to 90%. These nucleotide stretches can be
enough to allow plasmid integration at lbs locus via
homologous recombination, otherwise it will be unable
to propagate in Lactobacillus. An erythromycin resistance
marker (ermAM) was amplified from plasmid pRV566.
The Aequorea victoria GFP was PCR amplified from com-
mercial plasmid (Clontech, Palo Alto, CA, USA) and used
as reporter gene to test the expression of heterologous pro-
teins.
Sequencing and sequence analysis
DNA sequencing was carried out at the Núcleo de Análise
de Genoma e Expressão Gênica (NAGE), Instituto de
Ciências Biológicas, UniversidadeFederal de Minas
Gerais, Belo Horizonte, MG, Brazil, using a DYEnamic™
ET Dye Terminator Cycle Sequencing kit for MegaBACE™
DNA Analysis Systems (Amersham Biosciences, USA) in
combination with a MegaBACE™ 1000 automated
sequencing system. Both polynucleotide strands of the
cloned DNA were sequenced, using M13 forward and
reverse primers. The sequences obtained were compared
to sequences held in GenBank DNA database using the
BLAST algorithm [1].
Confocal scanning laser microscopy
Confocal microscopy work was performed using a LSM
510 META inverted confocal scanning laser microscope
(Carl Zeiss Ltd., Germany) carried out at the Centro de
Microscopia (CEMEL), Instituto de Ciências Biológicas,
Universidade Federal de Minas Gerais, Belo Horizonte,
MG, Brazil. Randomly selected areas of each sample were
imaged using a ×63 magnification objective with a numer-
ical aperture of 1.4. Confocal illumination was provided
by a Kr/Ar laser (458-nm laser excitation) fitted with a
long-pass 520-nm emission filter (greenfluorescence sig-
nal).
Authors' contributions
RMM, JLSM and MRS carried out all the experiments: dis-
section of chicks, bacteria isolation, DNA extraction, PCR
amplification, gel electrophoresis, restriction digestion,
and cloning. MFH and SMRT participated to the discus-
sion of the results, and the manuscript draft. EN and JRN
participated to the study design. ACN conceived and
designed the study, and coordinated and participated to
the manuscript draft. All authors read and approved the
final manuscript.
Acknowledgements
The authors acknowledge Maria Fernanda Brito de Almeida for technical
help during initial cloning experiments, Nirtes Schaper for chickens raise
and rearing, Fernanda Bastos for DNA sequencing, Carolina Cunha for con-
focal microscopy assistance, Elimar Faria and Jucélia Marize Pio for the val-
uable technical assistance. The work was supported by Conselho Nacional
de Desenvolvimento Científico e Tecnológico (CNPq) and Fundação de
Amparo à Pesquisa do Estado de Minas Gerais (FAPEMIG). JLSM, MFH,
SMRT and JRN are CNPq research fellows.
References
1. Altschul SF, Gish W, Miller W, Myers EW, Lipman DJ: Basic local
alignment search tool. J Mol Biol 1990, 215:403-410.
2. Avall-Jaaskelainen S, Palva A: Lactobacillus surface layers and
their applications. FEMS Microbiol Rev 2005, 29:511-529.
3. Bermudez-Humaran LG, Cortes-Perez NG, Le Loir Y, Alcocer-
Gonzalez JM, Tamez-Guerra RS, de Oca-Luna RM, Langella P: An
inducible surface presentation system improves cellular
immunity against human papillomavirus type 16 E7 antigen
in mice after nasal administration with recombinant lacto-
cocci. J Med Microbiol 2004, 53:427-33.
4. Bermudez-Humaran LG, Cortes-Perez NG, Lefevre F, Guimaraes V,
Rabot S, Alcocer-Gonzalez JM, Gratadoux JJ, Rodriguez-Padilla C,
Tamez-Guerra RS, Corthier G, Gruss A, Langella P: A novel
mucosal vaccine based on live Lactococci expressing E7 anti-
gen and IL-12 induces systemic and mucosal immune
responses and protects mice against human Papillomavirus
type 16-induced tumors. J Immunol 2005, 175:7297-302.
5. Boot HJ, Kolen CPAM, Andreadaki FJ, Leer RJ, Pouwels PH: The
Lactobacillus acidophilus S-layer protein gene expression site
comprises two consensus promoter sequences, one of which
directs transcription of stable mRNA. J Bacteriol 1996,
178(18):5388-5394.
6. Corthesy B, Boris S, Isler P, Grangette C, Mercenier A: Oral immu-
nization of mice with lactic acid bacteria producing Helico-
bacter pylori urease B subunit partially protects against
challenge with Helicobacter felis. J Infect Dis 2005,
192(8):1441-9.
7. Fuller R: Introduction. In Probiotics 2: Applications and Practical
Aspects Edited by: Fuller R. New York, Chapman & Hall; 1997:1-9.
8. Geoffroy M-C, Guyard C, Quatannens B, Pavan S, Lange M, Mercenier
A: Use of green fluorescent protein to tag lactic acid bacte-
rium strains under development as live vaccine vectors. Appl
Environ Microbiol 2000, 66:383-391.
9. Grangette C, Muller-Alouf H, Geoffroy M, Goudercourt D, Turneer
M, Mercenier A: Protection against tetanus toxin after intra-
gastric administration of two recombinant lactic acid bacte-
ria: impact of strain viability and in vivo persistence. Vaccine
2002, 20(27–28):3304-9.
10. Hughes HP, Boik RJ, Gerhardt SA, Speer CA: Susceptibility of
Eimeria bovis and Toxoplasma gondii to oxygen intermediates
and a new mathematical model for parasite killing. J Parasitol
1989, 75(4):489-497.