Streptococcus mutans is the leading cause of dental caries (tooth decay) worldwide and is considered to be the most cariogenic of all of the oral streptococci. The genome of S. mutans UA159, a serotype c strain, has been completely sequenced and is composed of 2,030,936 base pairs. It contains 1,963 ORFs, 63% of which have been assigned putative functions. The genome analysis provides further insight into how S. mutans has adapted to surviving the oral environment through resource acquisition, defense against host factors, and use of gene products that maintain its niche against microbial competitors. S. mutans metabolizes a wide variety of carbohydrates via nonoxidative pathways, and all of these pathways have been identified, along with the associated transport systems whose genes account for almost 15% of the genome. Virulence genes associated with extracellular adherent glucan production, adhesins, acid tolerance, proteases, and putative hemolysins have been identified. Strain UA159 is naturally competent and contains all of the genes essential for competence and quorum sensing. Mobile genetic elements in the form of IS elements and transposons are prominent in the genome and include a previously uncharacterized conjugative transposon and a composite transposon containing genes for the synthesis of antibiotics of the gramicidin͞bacitracin family; however, no bacteriophage genomes are present.

The 1,852,442-bp sequence of an M1 strain of Streptococcus pyogenes, a Gram-positive pathogen, has been determined and contains 1,752 predicted protein-encoding genes. Approximately onethird of these genes have no identifiable function, with the remainder falling into previously characterized categories of known microbial function. Consistent with the observation that S. pyogenes is responsible for a wider variety of human disease than any other bacterial species, more than 40 putative virulenceassociated genes have been identified. Additional genes have been identified that encode proteins likely associated with microbial ''molecular mimicry'' of host characteristics and involved in rheumatic fever or acute glomerulonephritis. The complete or partial sequence of four different bacteriophage genomes is also present, with each containing genes for one or more previously undiscovered superantigen-like proteins. These prophage-associated genes encode at least six potential virulence factors, emphasizing the importance of bacteriophages in horizontal gene transfer and a possible mechanism for generating new strains with increased pathogenic potential.

The complete nucleotide sequence was determined for the Streptococcus sobrinus MFe28 g#f gene, which encodes a glucosyltransferase that produces an insoluble glucan product. A single open reading frame encodes a mature glucosyltransferase protein of 1,559 amino acids (Mr, 172,983) and a signal peptide of 38 amino acids. In the C-terminal one-third of the protein there are six repeating units containing 35 amino acids of partial homology and two repeating units containing 48 amino acids of complete homology. The functional role of these repeating units remains to be determined, although truncated forms of glucosyltransferase containing only the first two repeating units of partial homology maintained glucosyltransferase activity and the ability to bind glucan. Regions of homology with alpha-amylase and glycogen phosphorylase were identified in the glucosyltransferase protein and may represent regions involved in functionally similar domains.The glucosyltransferases (EC 2.4.1.5) produced by various species of oral streptococci are of considerable interest because of their production of extracellular glucans from sucrose. These glucans are thought to play a key role in the development of dental plaque because of their ability to adhere to smooth surfaces and mediate the aggregation of bacterial cells and food debris (12). It is known that a single strain can produce several distinct glucosyltransferases differing in electrophoretic, antigenic, or enzymatic properties, although some of this apparent variety may be due to the use of different oral streptococcal strains and different purification procedures and activity assays by different laboratories. The properties and characteristics of the glucosyltransferases of the mutans group streptococci have been reviewed by Ciardi (3) and Mukasa (18).Recently, several glucosyltransferase genes from various strains of streptococci have been cloned by recombinant DNA techniques and have been shown to be expressed in Escherichia coli. Robeson et al. (24) have cloned a glucosyltransferase gene (gtfA) from Streptococcus mutans UAB90 (serotype c) and shown that it produces a protein with a molecular weight of 55,000. A similar gtfA gene has also been cloned by Pucci and Macrina (23) from S. mutans LM7 (serotype e) and by Burne et al. (2) from S. mutans GS5 (serotype c). Aoki et al. (1) reported the cloning of a glucosyltransferase gene (gtfB) from S. mutans GS-5 that produces a protein with a molecular weight of about 150,000. Another glucosyltransferase gene, gtfC, which specifies a 150,000-molecular-weight polypeptide has been obtained from S. mutans LM7 by Pucci et al. (22). Finally, Gilpin et al. (9) have cloned two glucosyltransferase genes from Streptococcus sobrinus MFe28 (serotype h): gtfS, which encodes a glucosyltransferase that synthesizes a watersoluble glucan, and gtfl, which encodes a glucosyltransferase that synthesizes a water-insoluble glucan.The availability of these cloned genes allows further characterization of both the genes and gene products, and in this ...

The gene specifying the bifunctional 6'-aminoglycoside acetyltransferase [AAC(6')] 2"-aminoglycoside phosphotransferase [APH(2")] enzyme from the Streptococcus faecalis plasmid pIP800 was cloned in Escherichia coli. A single protein with an apparent molecular weight of 56,000 was specified by this cloned determinant as detected in minicell experiments. Nucleotide sequence analysis revealed the presence of an open reading frame capable of specifying a protein of 479 amino acids and with a molecular weight of 56,850. The deduced amino acid sequence of the bifunctional AAC(6')-APH(2") gene product possessed two regions of homology with other sequenced resistance proteins. The N-terminal region contained a sequence that was homologous to the chloramphenicol acetyltransferase of Bacillus pumilus, and the C-terminal region contained a sequence homologous to the aminoglycoside phosphotransferase of Streptomyces fradiae. Subcloning experiments were performed with the AAC(6')-APH(2") resistance determinant, and it was possible to obtain gene segments independently specifying the acetyltransferase and phosphotransferase activities. These data suggest that the gene specifying the AAC(6')-APH(2") resistance enzyme arose as a result of a gene fusion.

The 1,815,783-bp genome of a serotype M49 strain of Streptococcus pyogenes (group A streptococcus [GAS]), strain NZ131, has been determined. This GAS strain (FCT type 3; emm pattern E), originally isolated from a case of acute post-streptococcal glomerulonephritis, is unusually competent for electrotransformation and has been used extensively as a model organism for both basic genetic and pathogenesis investigations. As with the previously sequenced S. pyogenes genomes, three unique prophages are a major source of genetic diversity. Two clustered regularly interspaced short palindromic repeat (CRISPR) regions were present in the genome, providing genetic information on previous prophage encounters. A unique cluster of genes was found in the pathogenicity island-like emm region that included a novel Nudix hydrolase, and, further, this cluster appears to be specific for serotype M49 and M82 strains. Nudix hydrolases eliminate potentially hazardous materials or prevent the unbalanced accumulation of normal metabolites; in bacteria, these enzymes may play a role in host cell invasion. Since M49 S. pyogenes strains have been known to be associated with skin infections, the Nudix hydrolase and its associated genes may have a role in facilitating survival in an environment that is more variable and unpredictable than the uniform warmth and moisture of the throat. The genome of NZ131 continues to shed light upon the evolutionary history of this human pathogen. Apparent horizontal transfer of genetic material has led to the existence of highly variable virulence-associated regions that are marked by multiple rearrangements and genetic diversification while other regions, even those associated with virulence, vary little between genomes. The genome regions that encode surface gene products that will interact with host targets or aid in immune avoidance are the ones that display the most sequence diversity. Thus, while natural selection favors stability in much of the genome, it favors diversity in these regions. Group A streptococcus ([GAS] Streptococcus pyogenes)causes a wide range of human diseases ranging from uncomplicated pharyngitis to life-threatening invasive disease. Acute post-streptococcal glomerulonephritis (APSGN) is one of the nonsuppurative sequelae that can occur following a GAS infection; the other common postinfection sequelae are rheumatic heart disease. Worldwide, it is estimated that approximately 470,000 cases of APSGN occur annually (23). Children and young adults are affected most commonly, with males having twice the incidence as females (74). By the 1940s, evidence was found that streptococcal skin infections were associated with APSGN, and these infections usually did not cause rheumatic fever, leading to the hypothesis that certain GAS strains were "rheumatogenic" while others were "nephritogenic" (41, 72). Further, divergent seasonal patterns of peak incidence exist separating nephritogenic and rheumatogenic GAS, with APSGN cases peaking in the late summer simultaneously with skin infections w...