Search

Streptolysin O (SLO) is a member of the thiol-activated cytolysins found in a number of Gram positive pathogenic bacteria. Often accompanying these cytolysins is a second gene first identified in Clostridium perfringens as the putative perfringolysin O regulator (pfoR). Members of the pfoR family are integral membrane proteins and exclusively found in exotoxin producing low %G+C Gram positive bacteria. The homolog of pfoR found in Streptococcus pyogenes is gene Spy0146 or slo R, a member of a three gene operon. In contrast to all other species, slo R is co-transcribed with another gene, Spy0145, a member of a large family of predicted transcriptional regulators of the yjg F family. The third gene (Spy0144) is a predicted DNA binding protein that may function as a regulator for the operon. We previously had shown that inactivation of SloR modulates the expression of SLO expression. To examine the effect of the slo R operon on SLO hemolysis, S. pyogenes strain NZ131 or its isogenic mutants for slo R (OK85) or Spy0144 (NZ131ΔSpy144) were grown in rich medium, with supernatant samples harvested between early-logarithmic and stationary phases. Trypan blue was used to inhibit SLS activity. Hemolysis in strain OK85 ( slo R-) was delayed as compared to wild type by approximately one cell division, while strain NZ131ΔSpy0144 showed an early expression of hemolysis as compared to wild type. The inactivation of Spy0144 appears to be related to increased expression of slo R and up-regulation of SLO. Restoration of a functional copy of Spy0144 on a bacteriophage integration vector was able to partially restore the wild type phenotype. The findings suggest that the slo R operon may encode an environmental sensor that relays some external signal to the cell, modulating the transcription of SLO through a yet to be determined molecular pathway.

The complete genome sequence of nine different strains of Streptococcus pyogenes have now been determined, including serotype M1 and M3 (two strains each), M5, M6, M18, M28, and M49. Seven of these strains are included in the class I type, known to be associated with either acute rheumatic fever or an invasive disease. Class II organisms are known to be associated with acute glomerulonephritis (AGN) and one of the best studied of this class is the M49 strain NZ131, the complete sequence of which has now been determined. The NZ131 (M49) genome contains 1,815,858 bp and is essentially colinear with the M1 genome; it contains no inversions around the origin or terminus. NZ131 contains several large blocks of DNA that appear to be insertions when compared to the class I genomes. These blocks do not appear to be mobile genetic elements, range in size from 3 to 28 kb, and contain a number of genes not found in any of the other sequenced strains. It is noteworthy that this genome contains only two complete bacteriophages—the least number of phages present in any of the previously described genomes. Interestingly, one of these phage genomes is inserted into the same location on the M49 genome as phage 370.2 on the M1 genome. Additionally, this phage contains a single superantigen gene (speH) at the attachment site, but not both speH and speI. A second phage genome contains a streptodornase gene at its attachment site. It is now becoming clear that homologous recombination between various prophages which share homology and residing in the same host can lead to host genome rearrangements and new associations with lysogenic conversion genes in phages. Further analysis of the unique M49 genes should provide important new information regarding virulence genes involved in AGN.

We report on a significant difference between the published nucleotide sequence of the Escherichia coli K12 histidine operon and our sequencing results repeatedly obtained from a number of different E. coli K12 strains. The discrepancies include 39 base-pair changes and one addition located predominantly in the proximal portion of the operon. Our data also suggest that neutral and near-neutral mutations do not accumulate to a significant extent in the histidine operon of E. coli strains harbouring strong mutator alleles.