Two alkaline motifs in the Lactobacillus salivarius Lv72 OppA surface are important to its adhesin function

Glycosaminoglycans are involved in the attachment of Lactobacillus salivarius Lv72, a strain of vaginal origin, to HeLa cell cultures, indicating that they play a fundamental role in the attachment of mutualistic bacteria to the epithelium lining cavities where the normal microbiota thrives. The bacterial OppA protein has been proposed as an adhesin involved in this adherence since, once purified, it significantly interferes with attachment of the lactobacilli to HeLa cell cultures. In this article, the role of OppA is confirmed through the determination of its location at the cell surface and its ability to promote Lactobacillus casei and Lactococcus lactis adherence to eukaryotic cell cultures upon cloning and expression of oppA in these bacteria. The OppA sequence showed five potential domains for glycosaminoglycan-binding, and structural modelling of the protein showed that two of them were located in the vicinity of an OppA superficial groove whose width approached the diameter of the helical form of heparin in solution. Their involvement in the binding was demonstrated through substitution of critical basic amino acids by acidic ones, which resulted in loss of affinity for heparan sulphate and chondroitin sulphate depending on the domain mutated, suggesting that there might be a certain degree of specialisation. In addition, circular dichroism analysis showed that the spectrum changes induced by OppA-heparan sulphate binding were attenuated by the variant proteins, indicating that these motifs are the OppA recognition domains for the eukaryotic cell surface.

Analysis of the morphogenetic cluster and genome of the temperate Lactobacillus casei bacteriophage A2

The genes that encode the morphogenetic proteins of bacteriophage A2 are clustered and expressed as a single operon which originates a late transcript of more than 20 kb. This DNA stretch is analyzed in the context of the whole phage genome, which presents the following peculiarities: a) the head presents two major proteins that share their NH(2) termini, i.e.: both are translated from a single gene (orf5), b) these two proteins suffer a proteolytic maturation process before being incorporated into the capsid, rendering a 123 NH(2) terminal putative polypeptide that is postulated to be the scaffolding protein of the phage, c) similar maturation processes occur at the portal and tail length determination proteins, having all in common a Pho-Pho-Arg downward arrow sequence (where Pho stands for any hydrophobic amino acid) at the processing point, d) the genes encoding the subunits of the terminase (orf61 and orf2) are separated by the cohesive ends, e) two genes that might mediate lysogenic conversion ( orf19 and orf22) have been identified and f) the genome presents a dispensable region (which covers at least 10 orfs, as judged from analysis of deletion mutants) that might be involved in maintaining its size between the packaging limits of the capsid.

Nucleotide sequence and analysis of pBL1, a bacteriocin-producing plasmid from Lactococcus lactis IPLA 972

The complete sequence of the 10.9-kbp bacteriocinogenic plasmid pBL1 from Lactococcus lactis subsp. lactis IPLA 972 has been determined. Thirteen ORFs were encountered, of which 5 were incomplete. pBL1 proved to be a narrow-host-range plasmid which replicates neither in Bacilus subtilis nor in Lactobacillus spp. The structural organization of the pBL1 replication region was highly similar to other well-known theta-replicating plasmids of lactococci, at both the untranslated (the replication origin) and the translated (repB and orfX) sequences. As in other plasmids, the product of orfX was not necessary for plasmid replication. However, it was shown to be involved in plasmid stability. Three genes organized in an operon-like structure encompassed, most likely, the bacteriocin-encoding region. Upstream of the origin of replication a nicking site (oriT) was found. This oriT sequence proved to be functional by mobilization of plasmids wearing it. One complete and several partial IS elements were identified on pBL1.

Characterization of the DNA replication module of bacteriophage A2 and use of its origin of replication as a defense against infection during milk fermentation by Lactobacillus casei

Adjacent to the lysis/lysogeny cassette of the A2 phage genome lies a stretch of over 8 kb, which contains a series of genes probably involved in DNA replication. Fifteen open reading frames (orfs) were identified, 13 of which are encoded on the main coding strand and only two on the complementary strand. Database searches and comparative analyses allowed the identification of an open reading frame (orf455) that shows similarity with DNA helicases and contains a variant zinc-finger motif known from the phage T7 helicase/primase. Orf770 showed similarity to putative plasmid and phage DNA primases. Downstream of orf770 is a noncoding 258-bp region rich in direct and inverted repeats, which specifically binds to proteins whose synthesis is induced during phage infection. When present in a plasmid, this region can direct a partial bacteriophage resistance phenotype due to interference with phage DNA replication, both under laboratory conditions and during milk fermentation. It is deduced that this stretch contains the origin of replication of phage A2.

Generation of food-grade recombinant lactic acid bacterium strains by site-specific recombination

The construction of a delivery and clearing system for the generation of food-grade recombinant lactic acid bacterium strains, based on the use of an integrase (Int) and a resolvo-invertase (beta-recombinase) and their respective target sites (attP-attB and six, respectively) is reported. The delivery system contains a heterologous replication origin and antibiotic resistance markers surrounded by two directly oriented six sites, a multiple cloning site where passenger DNA could be inserted (e.g., the cI gene of bacteriophage A2), the int gene, and the attP site of phage A2. The clearing system provides a plasmid-borne gene encoding beta-recombinase. The nonreplicative vector-borne delivery system was transformed into Lactobacillus casei ATCC 393 and, by site-specific recombination, integrated as a single copy in an orientation- and Int-dependent manner into the attB site present in the genome of the host strain. The transfer of the clearing system into this strain, with the subsequent expression of the beta-recombinase, led to site-specific DNA resolution of the non-food-grade DNA. These methods were validated by the construction of a stable food-grade L. casei ATCC 393-derived strain completely immune to phage A2 infection during milk fermentation.

A2 cro, the lysogenic cycle repressor, specifically binds to the genetic switch region of Lactobacillus casei bacteriophage A2

Lysogenic induction of temperate bacteriophage A2 of Lactobacillus casei is controlled by the action of its cI and cro products at the phage operator region. Three 20-bp inverted repeated DNA segments (subsites O1, O2, and O3) and the two divergent (PL and PR) promoters were mapped within the 153-bp operator region. The A2-encoded Cro product is shown to be the functional homolog of lambda Cro. The binding of Cro to the three operator subsites is noncooperative and yields two discrete protein-DNA complexes of retarded migration in mobility shift assays. The Kapp value for the Cro-PL-PR DNA complex was estimated to be 6 nM. Cro shows a slightly higher affinity for O3 than for O1 and O2 subsites. The O3 subsite overlaps the -35 hexamer of the PL promoter, which directs cI expression. A Cro mutant protein, devoid of the last 12 residues (Cro*), allowed the assignment of the DNA-binding domain to the NH2 end of Cro. The C end enhances its affinity for the DNA and probably stabilizes bending induced by Cro.

Solution structure of plantaricin C, a novel lantibiotic

Plantaricin C, a bacteriocin produced by a Lactobacillus plantarum strain of dairy origin, is a lantibiotic. One dehydroalanine, one lanthionine and three beta-methyl-lanthionine residues were found in its 27 amino acid sequence. The plantaricin C structure has two parts: the first comprises the six NH2-terminal residues, four of which are lysines, which confer a strong positive charge to this stretch. The amino acids in positions 7 and 27 form the lanthionine bridge, giving a globular conformation to the rest of the molecule. The beta-methyl-lanthionine bridges are established between residues 12-15, 13-18 and 23-26. This central region has a charge distribution compatible with an amphipathic alpha-helix, through which plantaricin C would become inserted into the membrane matrix of sensitive organisms, provoking the opening of pores and leakage of the cytoplasmic content.

Stable expression of the Lactobacillus casei bacteriophage A2 repressor blocks phage propagation during milk fermentation

A general strategy was applied to implement resistance against temperate bacteriophages that infect food fermentation starters through cloning and expression of the phage repressor. Lactobacillus casei ATCC 393 and phage A2 were used to demonstrate its feasibility as milk fermentation is drastically inhibited when the strain is infected by this phage. The engineered strain Lact. casei EM40::cI, which has the A2 repressor gene (cI) integrated into the genome, was completely resistant and able to ferment milk whether phage was present or not. In addition, viable phages were eliminated from the milk, probably through adsorption to the cell wall. Finally, the integration of cI in the genome resulted in a stable resistance phenotype, being unnecessary selective pressure during milk fermentation.

Cooperative interaction of CI protein regulates lysogeny of Lactobacillus casei by bacteriophage A2

The temperate bacteriophage A2 forms stable lysogens in Lactobacillus casei. The A2-encoded cI product (CI), which is responsible for maintaining the A2 prophage in the lysogenic state, has been purified. The CI protein, which is a monomer of 25.3 kDa in solution, specifically binds to a 153-bp DNA fragment that contains two divergent promoters, PL and PR. These promoters mediate transcription from cI and a putative cro, respectively. Three similar, although not identical, 20-bp inverted repeated DNA segments (operator sites O1, O2, and O3) were found in this segment. CI selectively interacts with O1, which is placed downstream from the transcription start point of the cro gene, and with O2 and O3, which overlap with the -35 region of the two promoters. Using a heterologous RNA polymerase, we have determined the transcription start points of PL and PR. CI exerts a negative effect on the in vitro transcription of PR by repositioning the RNA polymerase in a concentration-dependent manner. CI, when bound to O1 and O2, enhances the positioning of the RNA polymerase with the PL promoter. Our data indicate that the CI protein regulates the lytic and lysogenic pathways of the A2 phage.

Duplication of the beta-galactosidase gene in some Lactobacillus plantarum strains

Curing of a plasmid that encoded a beta-galactosidase gene (beta-gal) from the Lactobacillus plantarum strain of dairy origin LL441 was not accompanied by complete loss of the lactose utilization phenotype. DNA-DNA hybridization, using an internal fragment of the beta-gal gene as a probe, revealed a second determinant located on the chromosome of the cured derivatives. The chromosomal copy was present in all of a series of beta-Gal+ L. plantarum and Lactobacillus pentosus strains from different origins. In addition, four other L. plantarum strains harboured plasmid encoded beta-gal genes as well. Since both sequences cross-hybridized and present a similar genetic organization, it is postulated that the plasmid copy was generated through gene duplication and, probably, selected by growth of the strains in lactose rich environments.

The site-specific recombination system of the Lactobacillus species bacteriophage A2 integrates in gram-positive and gram-negative bacteria

The region of the bacteriophage A2 genome involved in site-specific recombination with the DNA of Lactobacillus spp. has been identified. Two orfs, transcribed from the same strand, have been found immediately upstream of the phage attachment site (attP). The orf adjacent to attP predicts a 385-amino-acid protein that presents significant similarity with site-specific recombinases of the integrase family. The other orf encodes a basic polypeptide of 76 amino acid residues. The junctions of the prophage with the genomes of its hosts have been determined, allowing the identification of the host attachment site (attB), which has a common 19-nucleotide core region with attP. The attB site is located at the 3' end of the transfer RNALeu gene (anticodon CAA). Nonreplicative plasmids containing the A2-specific recombination cassette integrate into different lactobacilli but also into unrelated Gram-positive bacteria such as Lactococcus lactis and even into Escherichia coli. In Lc. lactis, integration occurs in a previously unknown intergenic region, whereas in E. coli, it maps within the rrnD operon, 5' of rrsD gene. Comparison of the integration sites in the different hosts indicates that some flexibility is permitted in the attB sequence, since Lc. lactis and E. coli only share 13 and 11 nucleotides, respectively, with the 19-nucleotide core sequence of the lactobacilli.

Chemostat production of plantaricin C by Lactobacillus plantarum LL441

Plantaricin C, a bacteriocin synthesized by Lactobacillus plantarum LL441, was optimally produced in chemostats kept at pH 5.0, 30 degreesC, 150 rpm, and a dilution rate of 0.05 h-1 when glucose was used as carbon source and a dilution rate of 0.10 to 0.12 h-1 when sucrose or fructose was used instead. Production was abolished at high dilution rates, i.e., when the cells grew rapidly in all carbon sources.

Identification of the repressor-encoding gene of the Lactobacillus bacteriophage A2

The repressor gene of the Lactobacillus phage A2 has the following properties: it (i) encodes a 224-residue polypeptide with DNA binding and RecA cleavage motifs, (ii) is expressed in lysogenic cultures, and (iii) confers superinfection immunity on the host. Adjacent, but divergently transcribed, lies another open reading frame whose product resembles the lambda Cro protein. In the 161-bp intergenic segment, putative promoters and operators have been detected.

Adherence of human vaginal lactobacilli to vaginal epithelial cells and interaction with uropathogens

Three strains of Lactobacillus, identified as Lactobacillus acidophilus, Lactobacillus gasseri, and Lactobacillus jensenii, were selected from among 70 isolates from the vaginas of healthy premenopausal women for properties relevant to mucosal colonization or antagonism. All three self-aggregated and adhered to epithelial vaginal cells, displacing well-known vaginal pathogens, such as G. vaginalis, and inhibiting the growth in vitro of Escherichia coli and Streptococcus agalactiae. The surface components involved in self-aggregation appeared to be proteins for L. gasseri and lipoproteins for L. acidophilus and L. jensenii, as judged by susceptibility to treatment with appropriate degrading enzymes. The factors responsible for adherence to epithelial vaginal cells seemed to be glycoproteins (L. acidophilus and L. gasseri) and carbohydrate (L. jensenii). The receptors of the vaginal cells were glycolipids, which presumably were the targets of the competition observed between the lactobacilli and the pathogenic microbes.

Adherence of human vaginal lactobacilli to vaginal epithelial cells and interaction with uropathogens

Three strains of Lactobacillus, identified as Lactobacillus acidophilus, Lactobacillus gasseri, and Lactobacillus jensenii, were selected from among 70 isolates from the vaginas of healthy premenopausal women for properties relevant to mucosal colonization or antagonism. All three self-aggregated and adhered to epithelial vaginal cells, displacing well-known vaginal pathogens, such as G. vaginalis, and inhibiting the growth in vitro of Escherichia coli and Streptococcus agalactiae. The surface components involved in self-aggregation appeared to be proteins for L. gasseri and lipoproteins for L. acidophilus and L. jensenii, as judged by susceptibility to treatment with appropriate degrading enzymes. The factors responsible for adherence to epithelial vaginal cells seemed to be glycoproteins (L. acidophilus and L. gasseri) and carbohydrate (L. jensenii). The receptors of the vaginal cells were glycolipids, which presumably were the targets of the competition observed between the lactobacilli and the pathogenic microbes.

Isolation and characterization of promoters from the Lactobacillus casei temperate bacteriophage A2

Random Sau3A1 DNA fragments from the temperate Lactobacillus bacteriophage A2 were cloned into the promoter-probe plasmid pGKV210. Seven DNA fragments with promoter activity were selected, after transformation of Escherichia coli and Lactococcus lactis, subsp, lactis, through the chloramphenicol resistance they conferred to the corresponding clones. The seven promoters were functional in Lactobacillus casei. Their strength was analysed by measuring the levels of chloramphenicol resistance and chloramphenicol acetyltransferase activity induced in each host. The nucleotide sequences of these fragments were determined and primer extension analysis was used to locate the initiation site of transcription from each promoter in E coli. The promoters contained -10 and -35 regions similar to the consensus sequences of E. coli and Lactobacillus promoters.

Characterization of the aggregation promoting factor from Lactobacillus gasseri, a vaginal isolate

Lactobacillus gasseri 2459, isolated from the human vagina, exhibits a strong autoaggregating phenotype. Filter-sterilized spent supernatants of this strain promote aggregation of Lact. plantarum LL441 and Enterococcus faecalis EF. Aggregation was abolished upon exposure of the cells to proteases and, in the case of Ent. faecalis, to metaperiodate, which suggests the involvement of cell-surface proteins and glycoproteins, respectively, in the aggregation phenotype. In accordance with this, a 75 kDa surface protein, and possibly another of approximately 94 kDa, appears in Lact. plantarum LL441 cultures incubated with Lact. gasseri culture supernatants. The diffusible aggregation promoting factor was purified from stationary phase culture supernatants and determined to be a 2 kDa hydrophilic peptide active at pH 3-4 and stable at neutral and acid pH. The activity was resistant to heat, chymotrypsin, chelating agents, triton X-100 and reducing agents, but sensitive to other proteases and SDS.

Cloning and characterization of cspL and cspP, two cold-inducible genes from Lactobacillus plantarum

Two cold shock genes, cspL and cspP, have been cloned from two Lactobacillus plantarum strains. These genes, which are nonallelic, were present in all strains tested. The genes encode 66-amino-acid polypeptides related to each other and to the cold shock Csp family. Transcription of cspP rendered a single mRNA, while two cspL mRNAs were found with common 5' ends. The amounts of these transcripts increased moderately upon exposure of the cultures to cold.

Molecular analysis of the cos region of the Lactobacillus casei bacteriophage A2. Gene product 3, gp3, specifically binds to its downstream cos region

The terminal nucleotide sequence of the Lactobacillus casei bacteriophage A2 DNA revealed a single-stranded extension 13 bases in length (5'-AACGGTCGGCCTC-3') at its 3' termini that defines the packaging initiation nicking site (cosN). The cosN sequence is bisected by an axis of hyphenated twofold rotational symmetry. Directly and inverted repeated sequences located to the left (cosL) and the right (cosR) of the cosN site were observed. Analysis of the 3.4 kb EcoRI DNA sequence surrounding the cos region revealed four complete and one incomplete open reading frames (orfs). Northern blots indicated that all were cotranscribed in a single mRNA molecule in excess of 10 kb that appeared late during infection. Minicell studies indicated that the four orfs were translated into protein. From the ORF3 amino acid sequence DNA-binding and NTP-binding domains can be predicted. The purified ORF3 (predicted molecular mass 16.8 kDa) shows specific binding to the A2 cos region, so it was renamed gp3. Gp3 forms a specific complex with a 369 bp cos DNA segment in the presence of ATP. Gp3 interaction with the intrinsically bent cos DNA segment induces intramolecular ligation in the presence of T4 DNA ligase. The data presented here suggest that gp3 is the small subunit of the terminase enzyme.

Detection of fosfomycin resistance by the polymerase chain reaction and Western blotting

The polymerase chain reaction and Western blotting were assessed as means of detecting plasmid-encoded fosfomycin resistance in the hope that they might facilitate epidemiological studies. The results indicated good correlation between the two methods which are more rapid, less expensive and more sensitive than DNA-DNA hybridization. Both techniques could potentially be employed for the genotypic detection of resistance to any group of antibiotics.

Cloning and expression of the plasmid encoded beta-D-galactosidase gene from a Lactobacillus plantarum strain of dairy origin

The beta-galactosidase (beta-Gal) gene from Lactobacillus plantarum C3.8 was cloned and expressed in Lactococcus lactis and Escherichia coli. Hybridization experiments indicated that the gene is located on a plasmid and is present in other strains of Lactobacillus plantarum. Its sequence is very similar to a Leuconostoc lactis beta-Gal gene. Expression of the gene, both in Lactobacillus plantarum and in Lactococcus lactis, was four-fold higher in cells growth in lactose compared to those grown in glucose. The presence of the beta-Gal gene in Lactococcus lactis allowed this bacterium to be efficient in clotting milk.

Detection, purification, and partial characterization of plantaricin C, a bacteriocin produced by a Lactobacillus plantarum strain of dairy origin

A bacteriocin produced by Lactobacillus plantarum LL441 was selected from the inhibitory products of 75 mesophilic lactobacilli because of its potency and broad spectrum. It is a peptide of 3.5 kDa whose amino-terminal sequence is NH2-K-K-T-K-K-N-X-S-G-D-I-. It is bactericidal and, in some cases, bacteriolytic. The peptide, called plantaricin C, retained its activity after boiling, storage, and treatment at different pHs.

Global transcription pattern of phi C31 after induction of a Streptomyces coelicolor lysogen at different growth stages

Using two complementary strategies for low-resolution S1 mapping, the global pattern of phi C31 transcription was studied after induction of thermoinducible phi C31 lysogens of Streptomyces coelicolor A3(2). A complex pattern of early transcripts was seen, with a peak of abundance at about 10 min post-induction. Nearly all of these transcripts were from DNA located to the right of the c (repressor) gene and to the left of the attP site: a region of about 14 kb. Early transcription was also observed immediately to the left of the c gene. The c gene itself was also induced, with an earlier expression peak (about 5 min post-induction). Primary late transcripts were generally relatively long, but degraded. They apparently corresponded to most of the 18 kb region to the left of the c gene. Some shorter and more persistent late transcripts corresponded to DNA close to or overlapping the cos site. Large late transcripts from a region close to the left-hand end of the phi C31 genome showed evidence of processing to more stable, smaller RNA species. A failure of older cultures (more than 12 h old) to be induced productively was correlated with a much longer period of early transcription, reduced late transcription, failure to synthesize a major virion protein, and failure to package phi C31 DNA. Moreover, heat treatment of the older lysogenic cultures did not result in the phi C31-dependent shut-down of host rRNA transcription previously observed for young cultures (Rodríguez et al., Journal of General Microbiology (1986) 132, 1695-1701; Clayton & Bibb, Molecular Microbiology (1990) 4, 2179-2185).

Characterization of two aminoglycoside-(3)-N-acetyltransferase genes and assay as epidemiological probes

Two genes encoding for aminoglycoside-(3)-N-acetyltransferases (AAC(3)s) of different substrate patterns, present in multiresistance plasmids of hospital strains of Serratia marcescens and Escherichia coli isolated from urine, have been cloned and characterized. The first, aacC1 with AAC(3)I activity, contained a 531 base pair open reading frame which encodes a polypeptide of 177 aminoacids and 19,392 daltons, confirmed by minicell analysis. Its sequence differed from previously published work in four positions. Three of the changes did not alter the aminoacid sequence while the fourth was a substitution of an alanine by a proline. The second gene, an AAC(3)II encoded by aacC2, resulted from the translation of an 858 base pair open reading frame, which encoded a 286 aminoacid polypeptide of 31,574 daltons and was identical to those from plasmids isolated in Germany and the United States. However, the homology was broken in a position between the -10 and -35 promoter sequences, which resulted in different -35 hexanucleotides and levels of resistance conferred. The assay of both genes as molecular probes has revealed their specificity with respect to other aac genes, although their usefulness was limited in the case of aacC1 derived sequences to isolated plasmid DNA, since it hybridized under stringent conditions with chromosomal DNA of some strains of E. coli.

Cloning, sequencing, and use as a molecular probe of a gene encoding an aminoglycoside 6'-N-acetyltransferase of broad substrate profile

A gene coding for an aminoglycoside 6'-N-acetyltransferase that was able to modify amikacin was cloned from a plasmid isolated from a clinical strain of Enterobacter cloacae. Sequencing of a 955-bp segment which mediates the modifying activity revealed a single open reading frame of 432 nucleotides that predicted a polypeptide of 144 amino acid residues with a molecular weight of 16,021. Putative ribosomal binding sites and -10 and -35 sequences were located at the 5' end of the gene. The size of the polypeptide was confirmed through minicell analysis of the expression products of plasmids containing the sequence. The use of the gene as a molecular probe revealed its specificity toward strains harboring genes coding for related enzymes. This probe is therefore useful for epidemiological studies.

Structure of the DNA of five bacteriophages infecting Micromonospora

The physical maps of the DNA of five bacteriophages (Mm1, OM2, OM3, Mm4 and Mm5) which infect Micromonospora are presented. The restriction analyses showed that all of them had linear, double-stranded DNA, but only four (Mm1, OM2, Mm4 and Mm5) presented cohesive ends. The phages showed no relationship in terms of their restriction maps or of DNA-DNA hybridization, with the exception of Mm4 and Mm5, which resulted to be very similar. Phage Mm5 presented a high level of resistance to chelating agents, although deletion mutants, all of them showing a single detection of 1.4 kb, were obtained by using extremely selective conditions.

Purification of a glutathione S-transferase that mediates fosfomycin resistance in bacteria

The enzyme that modifies fosfomycin by formation of an adduct with glutathione was purified 12-fold with a 56% activity yield by passage through DEAE Sephacel and high-performance liquid chromatography molecular exclusion columns. Its functional form was a homodimer of two 16,000-dalton polypeptides, which possibly showed an antiparallel alpha tertiary structure and which lacked marked hydrophobic regions. Visualization of the reaction was achieved by precolumn derivatization of glutathione and the adduct, separation by high-performance liquid chromatography, and fluorescence detection of both compounds. Temperature and pH optima were 20 to 30 degrees C and 8.25, respectively; Mn2+, Fe2+, and Co2+ enhanced the rate of modification; and Km values were 9.4 and 11 mM for fosfomycin and glutathione, respectively. Phosphoenolpyruvate did not interfere with fosfomycin modification. The enzyme was stable at 4 degrees C for at least 6 months but progressively lost its activity upon being heated for 60 min at temperatures over 30 degrees C.

Purification and study of a bacterial glutathione S-transferase

A glutathione S-transferase from Escherichia coli has been purified approximately 800-fold with an 11% activity yield by passage through DEAE Sephacel and glutathione-agarose affinity columns. Its functional form is a homodimer of two 24,000 Da polypeptides that catalyzes the binding of glutathione and 1-chloro-2,4-dinitrobenzene with Km values of 0.25 and 1.5 mM, respectively. Optima of pH and temperature were 7.5 and 35 degrees C. The activity was stimulated (30%) by ethylenediaminetetraacetic acid. The N-terminal amino acid sequence was: Met-Leu-Leu-Phe-Ile-Leu-Pro-Gly-Ala.

[Ultrastructure of the intracellular development of bacteriophage phi C 31]

The intracellular development of the bacteriophage phi C31 in thermally induced cultures of the lysogen Streptomyces coelicolor 01 changes remarkably its cell structure. At 10 min post-induction, a big number of mesosomes are shown by the cells. At 30 min post-induction, the cytoplasm contains capsids which are still empty. At the end of the latent period mature virions are shown and immediately after, cell lysis occurs through the tip of germinative tubes. In old cultures (10 h or more) no viral progeny is detected. However, when the amino acid glycine is added to the culture medium, new virions are seen, but in smaller number than in germinating cultures. These results seem to indicate that the lysis happens at the tip of the germinative tubes probably because this is an area weakened by the preferential growth that takes place on it.

Formation of an adduct between fosfomycin and glutathione: a new mechanism of antibiotic resistance in bacteria

Plasmid-borne resistance to fosfomycin in bacteria is due to modification of the antibiotic molecule by a glutathione S-transferase that catalyzes the formation of a covalent bond between the sulfhydryl residue of the cysteine in glutathione and the C-1 of fosfomycin. This reaction results in opening of the epoxide ring of the antibiotic to form an inactive adduct, the structure of which was confirmed by nuclear magnetic resonance. Dialyzed extracts prepared from resistant Escherichia coli strains were unable to modify fosfomycin unless exogenous glutathione was added to the reaction mixtures. Similarly, mutants defective in glutathione biosynthesis were susceptible to fosfomycin, despite harboring a resistance plasmid. Extracts of resistant but not susceptible strains could join glutathione to 1-chloro-2,4-dinitrobenzene, confirming the nature of the enzymatic activity. Adduct formation appeared to be specific for glutathione: none of the other thiols tested (cysteine, N-acetylcysteine, and dithiothreitol) could modify fosfomycin.

The effect of rifampicin on the development of the Streptomyces bacteriophage phi C31

The production of phi C31 progeny virus was inhibited by rifampicin when it was added at any time before 20 minutes after induction of the thermoinducible lysogen Streptomyces coelicolor 01. The inhibition was gradually lost as the antibiotic was being added later on until the end of the latent period, which lasts about 45 minutes. This effect was not due to resistance of transcription to rifampicin but to accumulation of intracellular virions from around 20 minutes postinduction. When a rifampicin-resistant lysogen was induced in the presence of the antibiotic, no inhibition of RNA synthesis was detected, although a smaller population of progeny than in control cultures without rifampicin was obtained. Two possible explanations of this fact are discussed.

Transfection in Micromonospora spp

The introduction of bacteriophage DNA into Micromonospora protoplasts, resulting in the production of infective viral progeny, is reported. Transfection was affected by several factors. We observed that it reached a maximum when protoplasts from young mycelium (15 h old) were used. Maximum transfection took place when polyethylene glycol (PEG) was added to the mixtures at a final concentration of 20% (vol/vol) and did not occur at PEG concentrations under 10% or over 35%. The addition of positively charged liposomes to the mixtures was essential, since no transfectants were detected in the absence of liposomes at any PEG concentration. When DNA was present in nonlimiting amounts, a maximum efficiency of around 10(-3) to 10(-4) PFU per protoplast was obtained. The efficiency per DNA molecule showed a constant value of around 10(-4) to 10(-5) PFU, but the data suggest that transfection could be achieved by a single DNA molecule. The method proved to be equally efficient for the DNAs of at least five Micromonospora bacteriophages. On the contrary, we failed to transfect five of seven Micromonospora strains. These data suggest that only a minor subpopulation of protoplasts is competent and that the main factors influencing the transfection of Micromonospora protoplasts are neither the characteristics nor the origin of the DNA but the properties and status of the protoplasts.

Characteristics of the developmental cycle of actinophage phi C31

Some characteristics of the lytic development of the temperate phage phi C31 in Streptomyces coelicolor A3(2) were studied using a thermoinducible lysogen. The physiological state of the host and the culture medium influenced the production of progeny virus after induction. The latent period lasted 45 min and the rise period 20-30 min. RNA synthesis in induced cultures was reduced with respect to controls. This reduction was restricted to cellular transcription as evidenced by: no stable RNA being synthesized in induced cultures, and the proportion of phage specific RNA increasing from 0.5% before induction to more than 30% in induced cultures. Host RNA synthesis proceeded throughout the lytic cycle. Protein synthesis was also reduced in induced cultures, although to a lesser extent than RNA synthesis. Phage DNA synthesis started at around 10 min postinduction, marking the division between the early and late periods of phage development. Host DNA synthesis occurred during the first 20 min after induction, and gradually decreased later.

Cloning and molecular epidemiology of plasmid-determined fosfomycin resistance

The plasmid determinant of resistance to fosfomycin (For) was cloned into pBR322 and located in a 0.7-kilobase segment of DNA by transposon mutagenesis and in vitro deletion analysis. It encodes an 18-kilodalton protein located in the cytoplasm of resistant cells. Its synthesis is constitutive. The For genetic determinant is common to all plasmids isolated since 1975 in an hospital environment as determined by DNA-DNA hybridization. However, plasmids which carry For can be divided into two groups on the basis of size, pattern of antibiotic resistances, incompatibility specificity, and restriction and hybridization properties.

Fine structure, physiology and biochemistry of arthrospore germination in Streptomyces antibioticus

During germination, Streptomyces antibioticus arthrospores passed through stages: darkening, swelling and germ tube emergence. The first stage, darkening, whose main features were a decrease in absorbance and a loss of refractility, only required exogenous divalent cations (Ca2+, Mg2+ or Fe2+) and energy that can be obtained from the spore reserves. This stage was blocked by agents that inhibit ATP formation but not by antibiotics that inhibit macromolecular synthesis. The second stage, swelling, needed an exogenous carbon source and was not blocked by mitomycin C. In this stage, the spores exhibited the highest cytochrome oxidase and catalase activities and respiratory quotient. The last stage, germ tube emergence, required additional carbon and nitrogen sources. Ammonium compounds were superior to nitrate. Dry weight remained constant during the stages of darkening and swelling, with a rapid increase from the moment of germ tube emergence. Optimum pH and temperature for germination were 8.0 and 45 degrees C, respectively. Heat treatment (55 degrees C for 10 min) had no effect on germination. The fine structure of the spore underwent important changes during germination. The wall of the swollen spore became stratified and the inner layer was continuous with the germ tube wall. Macromolecular synthesis occurred in the sequence RNA, protein and then DNA. Rifampicin, streptomycin and mitomycin C prevented synthesis when added at the start of incubation. The same effect was obtained if the addition was made during germination, except with mitomycin C which inhibited DNA, but not RNA and protein synthesis.