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Journal of Bacteriology, January 2000, p. 155-163, Vol. 182, No. 1
Departamento de Biotecnología,
Instituto de Agroquímica y Tecnología de Alimentos,
CSIC, 46100 Burjassot, Spain
Received 14 June 1999/Accepted 3 October 1999
Genes encoding L-sorbose metabolism of
Lactobacillus casei ATCC 393 have been identified on a
6.8-kb chromosomal DNA fragment. Sequence analysis revealed
seven complete genes and a partial open reading frame transcribed as
two units. The deduced amino acid sequences of the first
transcriptional unit (sorRE) showed high similarity to the
transcriptional regulator and the L-sorbose-1-phosphate reductase of the sorbose (sor) operon
from Klebsiella pneumoniae. The other genes are transcribed
as one unit (sorFABCDG) in opposite direction to sorRE. The deduced peptide sequence
of sorF showed homology with the
D-sorbitol-6-phosphate dehydrogenase encoded in the
sor operon from K. pneumoniae and
sorABCD to components of the mannose
phosphotransferase system (PTS) family but especially to domains EIIA,
EIIB, EIIC and EIID of the phosphoenolpyruvate-dependent L-sorbose PTS from K. pneumoniae. Finally, the
deduced amino acid sequence of a truncated gene (sorG)
located downstream of sorD presented high similarity with
ketose-1,6-bisphosphate aldolases. Results of studies on
enzyme activities and transcriptional analysis revealed that the two
gene clusters, sorRE and sorFABCDG,
are induced by L-sorbose and subject to catabolite
repression by D-glucose. Data indicating that the
catabolite repression is mediated by components of the PTS elements and
by CcpA, are presented. Results of sugar uptake assays in
L. casei wild-type and sorBC mutant strains
indicated that L-sorbose is taken up by
L-sorbose-specific enzyme II and that L. casei
contains an inducible D-fructose-specific PTS. Results of
growth analysis of those strains and a man sorBC double
mutant suggested that L-sorbose is probably also
transported by the D-mannose PTS. We also present evidence,
from studies on a sorR mutant, suggesting that the
sorR gene encodes a positive regulator of the two
sor operons. Sequence alignment of SorR, SorC
(K. pneumoniae), and DeoR (Bacillus subtilis)
revealed that they might constitute a new group of transcriptional regulators.
0021-9193/0/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
Genetics of L-Sorbose Transport and
Metabolism in Lactobacillus casei

and
*
Corresponding author. Mailing address: Departamento de
Biotecnología, Instituto de Agroquímica y
Tecnología de Alimentos, CSIC, Apdo. Correos 73, 46100 Burjassot, Spain. Phone: 34-96-390-0022. Fax: 34-96-363-6301. E-mail:
gaspar.perez{at}iata.csic.es.
Present address: Department of Microbiology, Biologisch Centrum,
Rijksuniversiteit Groningen, 9759 AA Haren, The Netherlands.
Present address: Centro de Genetica e Biologia Molecular,
Departamento de Biologia Vegetal da Faculdade de Ciencias de Lisboa, Campo Grande, 1700 Lisbon, Portugal.
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