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The function of the S-layer, a regularly arranged structure on the outside of numerous bacteria, appears to be different for bacteria living in different environments. Almost no similarity exists between the primary sequences of S-proteins, although their amino acid composition is comparable. S-protein production is directed by single or multiple promoters in fron of the S-protein gene, yielding stable mRNAs. Most bacteria secrete S-proteins via the general secretory pathway (GSP). Translocation of S-protein across the outer membrane of Gram-negative bacteria sometimes occurs by S-protein-specific branches of the GSP. O-polysaccharide side-chains of the lipopolysaccharide component of the cell wall of Gram-negative bacteria appear to function as receptors for attachment of the S-layer. Silent S-protein genes have been found in Campylobacter fetus and Lactobaccillus acidophilus. These silent genes are placed in the expression site in a fraction of the bacterial population via inversiion of a chromosomal segment.

The outer membrane of Gram-negative bacteria contains proteins that might be good targets for vaccines, antimicrobials or detection systems. The identification of surface located proteins using traditional methods is often difficult. Yersinia pestis, the causative agent of plague, was labelled with biotin. Tagged proteins were visualised through streptavidin probing of Western blots. Seven biotinylated proteins of Y. pestis were identified including two porins and the putative virulence factor catalase peroxidase. Crown Copyright © 2006.

The most-dominant surface-exposed protein in many bacterial species is the S-protein. This protein crystallises into a regular monolayer on the outside surface of the bacteria: the S-layer. Lactobacillus acidophilus harbours two S-protein-encoding genes, slpA and slpB, only one of which (slpA) is expressed. In this study, we show by polymerase chain reaction (PCR) analysis that slpA and slpB are located on a 6 kb chromosomal segment, in opposite orientations. In a small fraction of the bacterial population, this segment is inverted. The inversion reads to interchanging of the expressed and silent S-protein-encoding genes, and places the formerly silent gene behind the S-promoter which is located outside the inverted segment. A 26 bp sequence showing a high degree of similarity with the consensus sequence recognized by the Din family of invertases is present in the region where recombination occurs. Expression of the slpA gene seems to be favoured under laboratory growth conditions because 99.7% of the chromosomes of an L. acidophilus ATCC 4356 broth culture had the slpA gene present at the sip expression site.

Invasive group A streptococcal (GAS) disease reemerged in The Netherlands in the late 1980s. To seek an explanation for this resurgence, the genetic compositions of 22 M1 and 19 M28 GAS strains isolated in The Netherlands between 1960s and the mid-1990s were analyzed by using a mixed-genome DNA microarray. During this four-decade period, M1 and especially M28 strains acquired prophages on at least eight occasions. All prophages carried a superantigen (speA2, speC, speK) or a streptodornase (sdaD2, sdn), both associated with invasive GAS disease. Invasive and noninvasive GAS strains did not differ in prophage acquisition, suggesting that there was an overall increase in the pathogenicity of M1 and M28 strains over the last four decades rather than emergence of hypervirulent subclones. The increased overall pathogenic potential may have contributed to the reemergence of invasive GAS disease in The Netherlands. Copyright © 2007, American Society for Microbiology. All Rights Reserved.

S-proteins are proteins which form a regular structure (S-layer) on the outside of the cell walls of many bacteria. Two S-protein-encoding genes are located in opposite directions on a 6.0-kb segment of the chromosome of Lactobacillus acidophilus ATCC 4356 bacteria. Inversion of this chromosomal segment occurs through recombination between two regions with identical sequences, thereby interchanging the expressed and the silent genes. In this study, we show that the region involved in recombination also has a function in efficient S-protein production. Two promoter sequences are present in the S-protein gene expression site, although only the most downstream promoter (P-1) is used to direct mRNA synthesis. S-protein mRNA directed by this promoter has a half-life of 15 min. Its untranslated leader can form a stable secondary structure in which the 5' end is base paired, whereas the ribosome- binding site is exposed. Truncation of this leader sequence results in a reduction in protein production, as shown by reporter gene analysis of Lactobacillus casei. The results obtained indicate that the untranslated leader sequence of S-protein mRNA is involved in efficient S-protein production.

Group A streptococci (GAS), or Streptococcus pyogenes, are associated with a remarkable variety of diseases, ranging from superficial infections to life-threatening diseases such as toxic-shock-like syndrome (TSS). GAS strains belonging to M types M1 and M3 are associated with TSS. This study aims to obtain insight into the gene profiles underlying different M types and disease manifestations. Genomic differences between 76 clinically well characterized GAS strains collected in The Netherlands were examined using a mixed-genome microarray. Inter-M-type genomic differences clearly outweighed intra-M-type genome variation. Phages were major contributors to observed genome diversification. We identified four novel genes, including two genes encoding fibronectin-binding-like proteins, which are highly specific to a subset of M types and thus may contribute to M-type-associated disease manifestations. All M12 strains were characterized by the unique absence of the citrate lyase complex and reduced growth under hypoxic, nutrient-deprived conditions. Furthermore, six virulence factors, including genes encoding a complement-inhibiting protein (sic), an exotoxin (speA), iron(III) binding factor, collagen binding factor (cpa), and fibrinogen binding factor (prt2-like), were unique to M1 and/or M3 strains. These virulence factors may contribute to the potential of these strains to cause TSS. Finally, in contrast to M-type-specific virulence profiles, we did not identify a common virulence profile among strains associated with TSS irrespective of their M type. Copyright © 2007, American Society for Microbiology. All Rights Reserved.