[Show abstract][Hide abstract] ABSTRACT: Protein folding in the envelope is a crucial limiting step of protein export and secretion. In order to better understand this process in Lactococcus lactis, a lactic acid bacterium, genes encoding putative exported folding factors like Peptidyl Prolyl Isomerases (PPIases) were searched for in lactococcal genomes.
In L. lactis, a new putative membrane PPIase of the cyclophilin subfamily, PpiA, was identified and characterized. ppiA gene was found to be constitutively expressed under normal and stress (heat shock, H(2)O(2)) conditions. Under normal conditions, PpiA protein was synthesized and released from intact cells by an exogenously added protease, showing that it was exposed at the cell surface. No obvious phenotype could be associated to a ppiA mutant strain under several laboratory conditions including stress conditions, except a very low sensitivity to H(2)O(2). Induction of a ppiA copy provided in trans had no effect i) on the thermosensitivity of an mutant strain deficient for the lactococcal surface protease HtrA and ii) on the secretion and stability on four exported proteins (a highly degraded hybrid protein and three heterologous secreted proteins) in an otherwise wild-type strain background. However, a recombinant soluble form of PpiA that had been produced and secreted in L. lactis and purified from a culture supernatant displayed both PPIase and chaperone activities.
Although L. lactis PpiA, a protein produced and exposed at the cell surface under normal conditions, displayed a very moderate role in vivo, it was found, as a recombinant soluble form, to be endowed with folding activities in vitro.
[Show abstract][Hide abstract] ABSTRACT: In the family Streptococcaceae, the genes encoding zinc ABC uptake systems (called zit or adc) are regulated by a coencoded MarR family member (i.e., ZitR or AdcR), whereas in the great majority of bacteria, these genes
are regulated by Zur, the Fur-like zinc-responsive repressor. We studied the zit operon from Lactococcus lactis and its regulation in response to Zn(II) in vivo. zit transcription is repressed by Zn(II) in a wide concentration range starting from nontoxic micromolar levels and is derepressed
at nanomolar concentrations. The level of zit promoter downregulation by environmental Zn(II) is correlated with the intracellular zinc content. The helix-turn-helix domain
of ZitR is required for downregulation. In vitro, the purified protein is a dimer that complexes up to two zinc ligands per monomer and specifically binds two intact palindromic
operator sites overlapping the −35 and −10 boxes of the zit promoter. DNA binding is abolished by the chelator EDTA or TPEN and fully restored by Zn(II) addition, indicating that the
active repressor complexes Zn(II) with high affinity. These results suggest that derepression under starvation conditions
could be an essential emergency mechanism for preserving Zn(II) homeostasis by uptake; under Zn(II)-replete conditions, the
function of ZitR repression could be to help save energy rather than to avoid Zn(II) toxicity. The characterization of a MarR
family zinc-responsive repressor in this report gives insight into the way Streptococcaceae efficiently adapt to Zn(II) fluctuations in their diverse ecological niches.
Full-text · Article · Feb 2011 · Journal of bacteriology
[Show abstract][Hide abstract] ABSTRACT: A Streptococcus mitis genomic DNA fragment carrying the SMT1224 gene encoding a putative β-galactosidase was identified, cloned, and expressed
in Escherichia coli. This gene encodes a protein 2,411 amino acids long with a predicted molecular mass of 268 kDa. The deduced protein contains
an N-terminal signal peptide and a C-terminal choline-binding domain consisting of five consensus repeats, which facilitates
the anchoring of the secreted enzyme to the cell wall. The choline-binding capacity of the protein facilitates its purification
using DEAE-cellulose affinity chromatography, although its complete purification was achieved by constructing a His-tagged
fusion protein. The recombinant protein was characterized as a monomeric β-galactosidase showing a specific activity of around
2,500 U/mg of protein, with optimum temperature and pH ranges of 30 to 40°C and 6.0 to 6.5, respectively. Enzyme activity
is not inhibited by glucose, even at 200 mM, and remains highly stable in solution or immobilized at room temperature in the
absence of protein stabilizers. In S. mitis, the enzyme was located attached to the cell surface, but a significant activity was also detected in the culture medium.
This novel enzyme represents the first β-galactosidase having a modular structure with a choline-binding domain, a peculiar
property that can also be useful for some biotechnological applications.
Full-text · Article · Aug 2009 · Applied and Environmental Microbiology
[Show abstract][Hide abstract] ABSTRACT: The nutritional requirement that Streptococcus pneumoniae has for the aminoalcohol choline as a component of teichoic and lipoteichoic acids appears to be exclusive to this prokaryote.
A mutation in the tacF gene, which putatively encodes an integral membrane protein (possibly, a teichoic acid repeat unit transporter), has been
recently identified as responsible for generating a choline-independent phenotype of S. pneumoniae (M. Damjanovic, A. S. Kharat, A. Eberhardt, A. Tomasz, and W. Vollmer, J. Bacteriol. 189:7105-7111, 2007). We now report
that Streptococcus mitis can grow in choline-free medium, as previously illustrated for Streptococcus oralis. While we confirmed the finding by Damjanovic et al. of the involvement of TacF in the choline dependence of the pneumococcus,
the genetic transformation of S. pneumoniae R6 by using S. mitis SK598 DNA and several PCR-amplified tacF fragments suggested that a minimum of two mutations were required to confer improved fitness to choline-independent S. pneumoniae mutants. This conclusion is supported by sequencing results also reported here that indicate that a spontaneous mutant of
S. pneumoniae (strain JY2190) able to proliferate in the absence of choline (or analogs) is also a double mutant for the tacF gene. Microscopic observations and competition experiments during the cocultivation of choline-independent strains confirmed
that a minimum of two amino acid changes were required to confer improved fitness to choline-independent pneumococcal strains
when growing in medium lacking any aminoalcohol. Our results suggest complex relationships among the different regions of
the TacF teichoic acid repeat unit transporter.
Full-text · Article · Jul 2008 · Journal of bacteriology
[Show abstract][Hide abstract] ABSTRACT: The use of Gram-positive bacteria for heterologous protein production proves to be a useful choice due to easy protein secretion and purification. The lactic acid bacterium Lactococcus lactis emerges as an attractive alternative to the Gram-positive model Bacillus subtilis. Here, we review recent work on the expression and secretion systems available for heterologous protein secretion in L. lactis, including promoters, signal peptides and mutant host strains known to overcome some bottlenecks of the process. Among the tools developed in our laboratory, inactivation of HtrA, the unique housekeeping protease at the cell surface, or complementation of the Sec machinery with B. subtilis SecDF accessory protein each result in the increase in heterologous protein yield. Furthermore, our lactococcal expression/secretion system, using both P(Zn)zitR, an expression cassette tightly controlled by environmental zinc, and a consensus signal peptide, SP(Exp4), allows efficient production and secretion of the staphylococcal nuclease, as evidenced by protein yields (protein amount/biomass) comparable to those obtained using NICE or P170 expression systems under similar laboratory conditions. Finally, the toolbox we are developing should contribute to enlarge the use of L. lactis as a protein cell factory.
Full-text · Article · Feb 2008 · Journal of Molecular Microbiology and Biotechnology
[Show abstract][Hide abstract] ABSTRACT: A novel Streptococcus pneumoniae plasmid (pSpnP1; 5413bp) has been isolated from the multidrug-resistant clone Poland(23F)-16, and its complete nucleotide sequence has been determined. Sequence analysis predicted seven co-directional open reading frames and comparative analyses revealed that plasmid pSpnP1 is different to pDP1, the only previously described pneumococcal plasmid, whereas it is highly similar to pSt08, a plasmid from Streptococcus thermophilus. A double-stranded origin for replication similar to the replication origin of the pC194/pUB110 family was located upstream of the putative rep gene (orf2). It also contained a 144-bp region with over 60% identity to the single-stranded origin type A of the Streptococcus agalactiae plasmid pMV158/pLS1. Detection of single-stranded DNA by Southern blot analysis indicated that pSpnP1 replicates via a rolling circle mechanism. Interestingly, the product of orf1 has a putative Zonular occludens toxin conserved domain present in toxigenic strains of Vibrio cholerae. Real-time PCR assays revealed that this ORF was expressed. Hybridization experiments showed that the pSpnP1 replicon was unusual among other examined antibiotic-resistant pneumococcal clones, although the recombinant plasmids based on pSpnP1 were able to replicate in Bacillus subtilis and Lactococcus lactis.
[Show abstract][Hide abstract] ABSTRACT: Miltefosine (hexadecylphosphocholine), the first oral drug against visceral leishmaniasis, triggered pneumococcal autolysis
at concentrations higher than 2.5 μM. Bactericidal activity was also observed in cultures of other streptococci, although
these failed to undergo lysis. The autolysis elicited by miltefosine can be attributed to triggering of the pneumococcal autolysin
Preview · Article · Jun 2007 · Antimicrobial Agents and Chemotherapy
[Show abstract][Hide abstract] ABSTRACT: Eight optochin-susceptible (Opts) alpha-hemolytic (viridans) streptococcus isolates were characterized at the molecular level. These isolates showed phenotypic
characteristics typical of both viridans streptococci and Streptococcus pneumoniae. Comparison of the sequence of housekeeping genes from these isolates with those of S. pneumoniae, Streptococcus mitis, Streptococcus oralis, and Streptococcus pseudopneumoniae suggested that the Opts isolates corresponded to streptococci of the mitis group. Besides, the Opts streptococci were negative by a Gen-Probe AccuProbe pneumococcus test and hybridized with specific pneumococcal probes (lytA and ply) but also with ant, a gene not present in most S. pneumoniae strains. Moreover, the isolates were insoluble in 1% sodium deoxycholate but completely dissolved in 0.1% deoxycholate. Sequence
analysis of the lytA gene revealed that the Opts streptococci carried lytA alleles characteristic of those present in nonpneumococcal streptococci of the mitis group. The determination of the partial
nucleotide sequence embracing the atp operon encoding the FoF1 H+-ATPase indicated that the optochin susceptibility of the isolates was due to the acquisition of atpC, atpA, and part of atpB from S. pneumoniae by horizontal gene transfer.
Full-text · Article · Dec 2006 · Journal of Clinical Microbiology
[Show abstract][Hide abstract] ABSTRACT: The nucleotide sequences of the lytA gene from 29 pneumococcal isolates of various serotypes and 22 additional streptococci of the mitis group (including two
Streptococcus pseudopneumoniae strains) have been compared and found to correspond to 19 typical (927-bp-long) and 20 atypical (921-bp-long) alleles. All
the Streptococcus pneumoniae strains harbored typical lytA alleles, whereas nonpneumococcal isolates belonging to the mitis group always carried atypical alleles. A sequence alignment
showed that the main difference between typical and atypical lytA alleles resided in 102 nucleotide positions (including the 6 bp absent from atypical alleles). These nucleotides were perfectly
conserved in all the typical alleles studied, and the corresponding nucleotides of the atypical alleles were also perfectly
conserved. The presence in these signatures of distinctive restriction sites (namely, SnaBI, XmnI, and BsaAI) allowed the
development of a simple, reliable, and fast method that combines PCR amplification of the lytA gene, digestion with BsaAI, and separation of the products by agarose gel electrophoresis. This assay allows the rapid and
consistent identification of true S. pneumoniae strains and represents an improved diagnostic tool for the study of pneumococcal carriage.
Preview · Article · May 2006 · Journal of Clinical Microbiology
[Show abstract][Hide abstract] ABSTRACT: The skl gene from Streptococcus mitis SK137 encodes a peptidoglycan hydrolase (Skl) that has been purified and biochemically characterized. Analysis of the degradation products obtained by digestion of pneumococcal cell walls with Skl revealed that this enzyme is an N-acetylmuramoyl-L-alanine amidase (EC 22.214.171.124), showing optimum activity at 30 degrees C and at a pH of 6.5. Skl is a unique member of the choline-binding family of proteins since it contains a cysteine, histidine-dependent amidohydrolases/peptidases (CHAP) domain. The CHAP domain of Skl showed homology to lysins of unknown especificity from a variety of streptococcal prophages. Skl represents the first characterized member of a new subfamily of CHAP-containing choline-binding proteins.
[Show abstract][Hide abstract] ABSTRACT: The capsular polysaccharide (CPS) is the most important identified virulence factor of Streptococcus pneumoniae, a human pathogen of the upper respiratory tract. One limitation in studies of S. pneumoniae surface virulence factors is the lack of a reliable procedure for isolation of capsule-negative mutants of clinical strains. This paper presents an approach, based on the immobilization of pneumococci in semi-liquid (0.04 % agar) medium, to easily distinguish and select for non-capsulated mutants. A clinical S. pneumoniae type 37 strain was used as a model to show that CPS production results in bacterial immobilization in semi-liquid agar medium and restricts cell sedimentation. Descendants of CPS(-) mutants sedimented faster under these conditions and therefore could be separated from immobilized parental cells. The CPS(-) phenotype of the obtained mutants was confirmed by both immunoagglutination and immunostaining experiments using specific type 37 capsular antibodies. Complementation of immobilization with the cloned tts gene, encoding type 37 CPS synthase, confirmed that faster sedimentation of mutants was specifically due to loss of the capsule. DNA sequence determination of three independent mutants revealed a point mutation, a 46 nt deletion and a heptanucleotide duplication in the tts gene. Immobilization of strains producing other CPSs (type 2, 3 and 6) also resulted in the appearance of CPS(-) mutants, thus showing that immobilization-based isolation is not restricted to type 37 pneumococci. Bacterial growth in semi-liquid medium proved to be a useful model system to identify the genetic consequences of immobilization. The results indicate that immobilization due to CPS may impose selective pressure against capsule production and thus contribute to capsule plasticity.
[Show abstract][Hide abstract] ABSTRACT: Here we developed the new expression system PZn zitR, based on the regulatory signals (PZn promoter and zitR repressor) of the Lactococcus lactis zit operon, involved in Zn2+ high-affinity uptake and regulation. A PZn zitR-controlled expression vector was constructed, and expression regulation was studied with two reporter genes, uspnuc and lacLM; these genes encode, respectively, a protein derived from Staphylococcus aureus secreted nuclease and Leuconostoc mesenteroides cytoplasmic β-galactosidase. Nuclease and β-galactosidase activities of L. lactis MG1363 cells expressing either uspnuc or lacLM under the control of PZn zitR were evaluated on plates and quantified from liquid cultures as a function of divalent metal ion, particularly Zn2+, availability in the environment. Our results demonstrate that PZn zitR is highly inducible upon divalent cation starvation, obtained either through EDTA addition or during growth in chemically
defined medium, and is strongly repressed in the presence of excess Zn2+. The efficiency of the PZn zitR expression system was compared to that of the well-known nisin-controlled expression (NICE) system with the same reporter
genes cloned under either PZn zitR or PnisA nisRK control. lacLM induction levels reached with both systems were on the same order of magnitude, even though the NICE system is fivefold more
efficient than the PZn zitR system. An even smaller difference or no difference was observed after 3 h of induction when nuclease was used as a reporter
for Western blotting detection. PZn zitR proved to be a powerful expression system for L. lactis, as it is tightly controlled by the zinc concentration in the medium.
Preview · Article · Oct 2004 · Applied and Environmental Microbiology
[Show abstract][Hide abstract] ABSTRACT: Many streptococci are human and/or animal pathogens and the frequent cause of life-threatening diseases. Among various streptococcal virulence factors, capsular polysaccharides (CPs) are recognized as essential to prevent phagocytosis by macrophages and neutrophils. In the last decade, an impressive advance on the knowledge of the genetic bases underlying capsule formation has been achieved. The capsular gene cluster driving the formation of the CP of Streptococcus pyogenes and other hyaluronate-producing streptococci, represents one of the simplest cases of gene organization to synthesize a capsule. A more complex situation has been found in Streptococcus pneumoniae, Streptococcus agalactiae, Streptococcus suis, and other streptococci. On the whole, there exists a direct relationship between the structural and chemical complexity of the repeating unit of the polysaccharide and the number of genes found in the corresponding capsular locus. Streptococcal vaccines, either polysaccharide or conjugate, are currently being tested in clinical trials to overcome the rise of worldwide antibiotic resistance, although, for different reasons, none of these vaccines are expected to provide the required full coverage in a near future. This concern has prompted to explore alternative possibilities with an improved therapeutic potential against streptococcal diseases.
No preview · Article · Oct 2001 · Current Molecular Medicine
[Show abstract][Hide abstract] ABSTRACT: The type 37 capsule of Streptococcus pneumoniae is a homopolysaccharide built up from repeating units of [β-d-Glcp-(1→2)]-β-d-Glcp-(1→3). The elements governing the expression of the tts gene, coding for the glucosyltransferase involved in the synthesis of the type 37 pneumococcal capsular polysaccharide, have
been studied. Primer extension analysis and functional tests demonstrated the presence of four new transcriptional start points
upstream of the previously reported tts promoter (ttsp). Most interesting, three of these transcriptional start points are located in a RUP element thought to be involved in recombinational
events (Oggioni, M. R., and Claverys, J. P. (1999) Microbiology145, 2647–2653). Transformation experiments using either a recombinant plasmid containing the whole transcriptional unit of
tts or chromosomal DNA from a type 37 pneumococcus showed that ttsis the only gene required to drive the biosynthesis of a type 37 capsule in S. pneumoniae and other Gram-positive bacteria, namely Streptococcus oralis, Streptococcus gordonii, andBacillus subtilis. The Tts synthase was overproduced inS. pneumoniae and purified as a membrane-associated enzyme. These membrane preparations used UDP-Glc as substrate to catalyze the synthesis
of a high molecular weight polysaccharide immunologically identical to the type 37 capsule. In addition, UDP-Gal was also
a substrate to produce type 37 polysaccharide since a strong UDP-Glc-4′-epimerase activity is associated to the membrane fraction
ofS. pneumoniae. These results indicated that Tts has a dual biochemical activity that leads to the synthesis of the branched type 37 polysaccharide.
Preview · Article · Jun 2001 · Journal of Biological Chemistry
[Show abstract][Hide abstract] ABSTRACT: The capsular gene cluster (cap/cps) of 13 out of the 90 known pneumococcal types has been sequenced. The cap/cps operon, located between dexB and aliA in the Streptococcus pneumoniae chromosome, contains some of the genes responsible for the synthesis of the type-specific polysaccharide flanked by four conserved open reading frames. The biochemical function of only a few capsular genes has been established, whereas the role of the flanking regions is controversial. Remarkably, only one gene (tts) located outside the cap locus is required for the synthesis of type 37 capsule. Moreover, other genes not linked to the cap gene cluster are also needed for capsule synthesis in pneumococcus.
Full-text · Article · Jul 2000 · Research in Microbiology
[Show abstract][Hide abstract] ABSTRACT: It has been recently reported that different type 37 clinical isolates of Streptococcus pneumoniae have an identical tts gene directing the formation of type 37 capsular polysaccharide. Here we show that type 37 S. pneumoniae strains isolated in two different continents (Europe and America) some 60 years apart frequently gave rise to nontypable variants upon in vitro cultivation. The tts gene from three independent nontypable mutants was PCR amplified and sequenced showing different classes of inactivating mutations. Furthermore, pulsed-field gel electrophoresis and multilocus sequence typing demonstrated that the type 37 pneumococcal isolates studied so far constitute a highly related strain cluster (a clonal complex), and strongly suggested that every type 37 pneumococcus has spread globally from a single, old clone.
No preview · Article · Feb 2000 · Microbial Drug Resistance
[Show abstract][Hide abstract] ABSTRACT: Streptococcus pneumoniae is a major human pathogen and its capsular polysaccharide has been shown to be the main virulence factor. The molecular organization of the genes governing the formation of this capsule was not studied until the 1990s. The capsular clusters (cap) of eight of the 90 known pneumococcal types have now been studied. The cap operon, located between the dexB and aliA genes, is arranged as a central region comprising the genes coding for the specific-type polysaccharide, flanked by open reading frames that are mostly common to all of the serotypes. The biochemical functions of 24 genes required for capsular polysaccharide biosynthesis have been elucidated but the precise role of the flanking regions in capsular formation is unknown. The natural genetic transformation characteristic of pneumococci, the arrangement of the cap locus and the abundance of transposable elements at this locus favor the genetic variability of the capsule in this microorganism. These well-documented observations together with the finding that some genes located outside the cap cluster may also participate in capsule formation increase the complexity of pneumococcal infection control.
No preview · Article · Oct 1999 · International Microbiology
[Show abstract][Hide abstract] ABSTRACT: The molecular aspects of the type 37 pneumococcal capsular biosynthesis, a homopolysaccharide composed of sophorosyl units (beta-d-Glc-(1-->2)-beta-d-Glc) linked by beta-1,3 bonds, have been studied. Remarkably, the biosynthesis of the type 37 capsule is driven by a single gene (tts) located far apart from the cap locus responsible for capsular formation in all of the types characterized to date in Streptococcus pneumoniae. However, a cap37 locus virtually identical to the cap33f cluster has been found in type 37 strains, although some of its genes are inactivated by mutations. The tts gene has been sequenced and its transcription start point determined. Tts shows sequence motifs characteristic of cellulose synthases and other beta-glycosyltransferases. Insertion of the tts gene into the pneumococcal DNA causes a noticeable genome reorganization in such a way that genes normally separated by more than 350 kb in the chromosome are located together in clinical isolates of type 37. Encapsulated pneumococcal strains belonging to 10 different serotypes (or serogroups) transformed with tts synthesized type 37 polysaccharide, leading to the formation of strains that display the binary type of capsule. Type 37 pneumococcus constitutes the first case of a natural, genetically binary strain and represents a novel alternative to the mechanisms of intertype transformation.
Preview · Article · Aug 1999 · Journal of Experimental Medicine