(1/1064) Complete genomic sequence of the lytic bacteriophage DT1 of Streptococcus thermophilus.
Streptococcus thermophilus lytic bacteriophage DT1, isolated from a mozzarella whey, was characterized at the microbiological and molecular levels. Phage DT1 had an isometric head of 60 nm and a noncontractile tail of 260 x 8 nm, two major structural proteins of 26 and 32 kDa, and a linear double-stranded DNA genome with cohesive ends at its extremities. The host range of phage DT1 was limited to 5 of the 21 S. thermophilus strains tested. Using S. thermophilus SMQ-301 as a host, phage DT1 had a burst size of 276 +/- 36 and a latent period of 25 min. The genome of phage DT1 contained 34,820 bp with a GC content of 39.1%. Forty-six open reading frames (ORFs) of more than 40 codons were found and putative functions were assigned to 20 ORFs, mostly in the late region of phage DT1. Comparative genomic analysis of DT1 with the completely sequenced S. thermophilus temperate phage O1205 revealed two large homologous regions interspersed by two heterologous segments. The homologous regions consisted of the early replication genes, the late morphogenesis genes, and the lysis cassette. The divergent segments contained the DNA packaging machinery, the major structural proteins, and remnants of a lysogeny module. (+info)
(2/1064) Purification and properties of bacteriolytic enzymes from Bacillus licheniformis YS-1005 against Streptococcus mutans.
To find a novel lytic enzyme against cariogenic Streptococci, strains showing strong lytic activity have been screened from soil using Streptococcus mutans. A strain identified as Bacillus licheniformis secreted two kinds of lytic enzymes, which were purified by methanol precipitation, CM-cellulose chromatography, gel filtration, and hydroxyapatite chromatography. The molecular weights of these two enzymes, L27 and L45, were 27,000 and 45,000, respectively. Optimum pH and temperature of both enzymes for lytic activity were pH 8 and 37 degrees C. L27 and L45 digest the peptide linkage between L-Ala and D-Glu in peptidoglycan of Streptococcus mutans. The lytic activity was highly specific for Streptococcus mutans, suggesting their potential use as a dental care product. (+info)
(3/1064) Structural and functional analysis of pCI65st, a 6.5 kb plasmid from Streptococcus thermophilus NDI-6.
The 6.5 kb cryptic plasmid pCI65st from Streptococcus thermophilus NDI-6, a strain isolated from the Indian fermented milk dahi, was subcloned and sequenced. Five putative ORFs were identified. ORF1 could encode a 315 aa polypeptide almost identical to the RepA protein of previously sequenced S. thermophilus plasmids, indicating that pCI65st is one of the pC194 group of small gram-positive rolling-circle plasmids. ORFs 2 and 4 were virtually identical and could specify proteins of approximately 150 aa with significant similarity to the small heat-shock proteins described from a variety of gram-positive bacteria. ORF3 could encode a 415 aa protein similar to enolase, an enzyme involved in glycolysis and gluconeogenesis. ORF5 could encode a 412 aa protein which had high similarity to the HsdS (specificity) proteins of type I restriction-modification systems. Variants of strain NDI-6 which lacked pCI65st were readily isolated after subculture of the parent strain at 32 degrees C. The plasmid-bearing parent culture was significantly more resistant to a temperature shift from 42 degrees C to 62 degrees C than its plasmid-free variant and expressed proteins which corresponded with the predicted translation products from ORF2 and ORF4. In addition, plasmid-free mutants were lysed in broth by bacteriophages to which the parent culture was resistant. (+info)
(4/1064) Partial characterization of a major autolysin from Mycobacterium phlei.
Autolytic enzyme profiles of fast- and slow-growing mycobacteria were examined using SDS-PAGE zymography with incorporated mycobacterial peptidoglycan sacculi as substrate. Each species tested (Mycobacterium phlei, Mycobacterium smegmatis, Mycobacterium aurum, Mycobacterium fortuitum and Mycobacterium kansasii) appeared to produce a different set of enzymes on the basis of differing number and molecular masses. A major autolysin from M. phlei was purified to apparent homogeneity by DEAE-cellulose chromatography, preparative gel electrophoresis and Mono Q FPLC. This enzyme had an estimated molecular mass of 38 kDa, an isoelectric point of 5.5 and a pH optimum of pH 7.5. Digestion of purified peptidoglycan by the enzyme resulted in the appearance of reducing sugars, suggesting that the 38 kDa autolysin is a beta-glycosidase. Partial internal amino acid sequence of the autolysin was determined and should facilitate identification, cloning and overexpression of the encoding gene. (+info)
(5/1064) Bacillus subtilis 168 gene lytF encodes a gamma-D-glutamate-meso-diaminopimelate muropeptidase expressed by the alternative vegetative sigma factor, sigmaD.
A gamma-D-glutamate-meso-diaminopimelate muropeptidase was detected in the vegetative growth phase of Bacillus subtilis 168. It is encoded by the monocistronic lytF operon expressed by the alternative vegetative sigma factor, sigmaD. Sequence analysis of LytF revealed two domains, an organization common to exoproteins of B. subtilis as well as to those from other organisms. The N-terminal domain contains a fivefold-repeated motif attributed to cell wall binding, whilst the C-terminal domain is probably endowed with the catalytic activity. Overexpression of LytF allowed its purification and biochemical characterization. Inactivation of lytF led to the loss of the cell-wall-bound protein 49' (CWBP49') and of the corresponding lytic activity as revealed by renaturation gel assay. Native cell walls prepared from the multiple lytC lytD lytE lytF-deficient mutant did not exhibit any autolysis, whereas walls prepared from a strain endowed with LytF but not with the other three enzymes underwent a slight lysis. Analysis of degradation products of cell wall devoid of teichoic-acid-bound O-esterified D-alanine unambiguously confirmed that LytF cuts the gamma-D-glutamate-mesodiaminopimelate bond. (+info)
(6/1064) A theoretical and empirical investigation of the invasion dynamics of colicinogeny.
A mathematical model describing the dynamics of a colicinogenic and a colicin-sensitive population propagated under serial transfer culture conditions was formulated. In addition, a series of in vitro invasion experiments using six representatives of the E colicin group was undertaken, together with the estimation of the growth rates and colicinogenic characteristics of the strains. Growth rates among the strains varied by up to 44%. There were 14-fold differences among strains in their lysis rates and there were up to 10-fold differences in the amount of colicin produced per lysed cell. The in vitro serial transfer invasion experiments revealed that regardless of initial frequency all colicinogenic strains succeeded in displacing the sensitive cell populations. The amount of time required for the colicin-sensitive cell population to be displaced declined as the initial frequency of the colicinogenic population increased and strains producing higher titres of colicin tended to displace the sensitive strain more rapidly. Overall, the observed dynamics of the invasion of colicinogenic strains was adequately described by the theoretical model. However, despite there being substantial differences among the strains in their growth rates and colicinogenic characteristics there were relatively few differences, observed or predicted, in the invasion dynamics of the six colicinogenic strains. These results suggest that the characteristics of different colicinogenic strains cannot be used to explain the extensive variation in the relative abundance of different colicins in natural populations of bacteria. (+info)
(7/1064) The C-terminal sequence of the lambda holin constitutes a cytoplasmic regulatory domain.
The C-terminal domains of holins are highly hydrophilic and contain clusters of consecutive basic and acidic residues, with the overall net charge predicted to be positive. The C-terminal domain of lambda S was found to be cytoplasmic, as defined by protease accessibility in spheroplasts and inverted membrane vesicles. C-terminal nonsense mutations were constructed in S and found to be lysis proficient, as long as at least one basic residue is retained at the C terminus. In general, the normal intrinsic scheduling of S function is deranged, resulting in early lysis. However, the capacity of each truncated lytic allele for inhibition by the S107 inhibitor product of S is retained. The K97am allele, when incorporated into the phage context, confers a plaque-forming defect because its early lysis significantly reduces the burst size. Finally, a C-terminal frameshift mutation was isolated as a suppressor of the even more severe early lysis defect of the mutant SA52G, which causes lysis at or before the time when the first phage particle is assembled in the cell. This mutation scrambles the C-terminal sequence of S, resulting in a predicted net charge increase of +4, and retards lysis by about 30 min, thus permitting a viable quantity of progeny to accumulate. Thus, the C-terminal domain is not involved in the formation of the lethal membrane lesion nor in the "dual-start" regulation conserved in lambdoid holins. Instead, the C-terminal sequence defines a cytoplasmic regulatory domain which affects the timing of lysis. Comparison of the C-terminal sequences of within holin families suggests that these domains have little or no structure but act as reservoirs of charged residues that interact with the membrane to effect proper lysis timing. (+info)
(8/1064) Characterization of a chromosomally encoded glycylglycine endopeptidase of Staphylococcus aureus.
The authors previously reported the cloning of a lytic-enzyme-encoding gene, lytM, from an autolysis-defective mutant of Staphylococcus aureus. In the present work, the lytM gene was overexpressed in Escherichia coli and the product was purified to homogeneity by affinity chromatography and HPLC. Biochemical analysis of LytM-cleaved peptidoglycan fragments indicated that LytM is a glycylglycine endopeptidase. Immunoelectron microscopic studies with anti-LytM rabbit IgG showed that LytM is expressed during the early exponential phase and is overexpressed in an autolysis-defective mutant compared with the parent strain. Also, a uniform distribution of gold particles on the surface of actively growing bacterial cells indicates that LytM plays a role in cell growth. Northern blot analyses of lytM expression in two global regulatory mutants, agr and sar, showed that expression of lytM is increased about twofold in these mutants as compared with the parents. Protein homology searches revealed that LytM could be a member of the zinc protease family, as it contained a homologous 38-amino-acid motif, Tyr-X-His-X11-Val-X12/20-Gly-X5-6-His. Atomic absorption spectrometric analysis of LytM revealed the presence of 0.9 mol zinc (mol LytM)(-1). (+info)