Basic streptococcal superantigens (SPEX/SMEZ or SPEC) are responsible for the mitogenic activity of the so-called mitogenic factor (MF)

The mitogenic factor (MF) of group A streptococci has been reported to be a superantigen stimulating human T cells carrying Vbeta2, 4 and 8 and has been designated streptococcal pyrogenic exotoxin F (SPEF). MF was also shown to possess DNase activity. Here we have purified MF from culture supernatants of different Streptococcus pyogenes strains. Surprisingly, the MF preparations from different strains showed different Vbeta specificities depending on the expression of SPEC or SMEZ3 by the producing strain. Their mitogenic activity decreased upon further purification. In addition, the mitogenic activity could be only neutralized by antibodies against the basic streptococcal superantigens SPEC or SPEX (SMEZ3) but not by antibodies against MF itself although the latter were able to neutralize completely the DNase activity of MF. We found that streptodornase type B (SDB) was expressed in two molecular forms (SDBI and SDBII), differing only by one additional N-terminal arginine at SDBI. MF was found identical to the enzyme SDBII but is devoid of superantigenic properties and should no longer be called a superantigen or a pyrogenic exotoxin.     

Differential secretomics of Streptococcus pyogenes reveals a novel peroxide regulator (PerR)-regulated extracellular virulence factor mitogen factor 3 (MF3)

Streptococcus pyogenes is a human pathogen that causes various diseases. Numerous virulence factors secreted by S. pyogenes are involved in pathogenesis. The peroxide regulator (PerR) is associated with the peroxide resistance response and pathogenesis, but little is known about the regulation of the secretome involved in virulence. To investigate how PerR regulates the expression of the S. pyogenes secretome involved in virulence, a perR deficient mutant was used for comparative secretomic analysis with a wild-type strain. The conditioned medium containing secreted proteins of a wild-type strain and a perR deficient mutant at the stationary phase were collected for two-dimensional gel electrophoresis analysis, where protease inhibitors were applied to avoid the degradation of extracellular proteins. Differentially expressed protein spots were identified by liquid chromatography electrospray ionization tandem MS. More than 330 protein spots were detected on each gel. We identified 25 unique up-regulated proteins and 13 unique down-regulated proteins that were directly or indirectly controlled by the PerR regulator. Among these identified proteins, mitogen factor 3 (MF3), was selected to verify virulence and the expression of gene products. The data showed that MF3 protein levels in conditioned medium, as measured by immunoblot analysis, correlated well with protein levels determined by two-dimensional gel electrophoresis analysis. We also demonstrated that PerR bound to the promoter region of the mf3 gene. The result of an infection model showed that virulence was attenuated in the mf3 deficient mutant. Additional growth data of the wild-type strain and the mf3 deficient mutant suggested that MF3 played a role in digestion of exogenous DNA for promoting growth. To summarize, we conclude that PerR can positively regulate the expression of the secreted protein MF3 that contributes to the virulence in S. pyogenes. The analysis of the PerR-regulated secretome provided key information for the elucidation of the host-pathogen interactions and might assist in the development of potential chemotherapeutic strategies to prevent or treat streptococcal diseases.     

苏云金杆菌毒素调控基因plcR的特性与表达

根据蜡状芽胞杆菌plcR基因和papR基因序列设计特异引物,对6个Bt菌株（WB1、WB7、WB9、HD98、8010、8311）及5个Bc菌株（6A1、6A2、6A3、6A4、6S1）进行了PCR检测.结果显示,3个Bt菌株及4个Bc菌株含有plcR-papR基因.克隆了Bt8010、Bc6A2和6A3的plcR、papR基因,核苷酸序列分析表明,三个菌株的plcR、papR基因与NCBI数据库中的Bt、Bc及Ba相应序列都有很高的相似性.Bt8010的plcR基因编码框由846个核苷酸组成,可编码282个氨基酸;papR基因的编码框由144个核苷酸组成,可编码48个氨基酸.推导的氨基酸序列分析表明,Bt8010 的PapR有21个氨基酸的信号肽序列,PlcR没有信号肽序列.与Bc6A2、6A3和Bc 569相比,Bt8010 的PlcR和PapR在氨基酸序列上与Bc 相应序列存在相对较大的差异.将plcR-papR基因连接到表达载体pHT304中,并转化至大肠杆菌JM109中成功进行了表达,为研究Bt plcR基因的功能奠定了基础.     

The S2 gene nucleotide sequences of prototype strains of the three reovirus serotypes: characterization of reovirus core protein sigma 2.

The S2 gene nucleotide sequences of prototype strains of the three reovirus serotypes were determined to gain insight into the structure and function of the S2 translation product, virion core protein sigma 2. The S2 sequences of the type 1 Lang, type 2 Jones, and type 3 Dearing strains are 1,331 nucleotides in length and contain a single large open reading frame that could encode a protein of 418 amino acids, corresponding to sigma 2. The deduced sigma 2 amino acid sequences of these strains are very conserved, being identical at 94% of the sequence positions. Predictions of sigma 2 secondary structure and hydrophobicity suggest that the protein has a two-domain structure. A larger domain is suggested to be formed from the amino-terminal three-fourths of sigma 2 sequence, which is separated from a smaller carboxy-terminal domain by a turn-rich hinge region. The carboxy-terminal domain includes sequences that are more hydrophilic than those in the rest of the protein and contains sequences which are predicted to form an alpha-helix. A region of striking similarity was found between amino acids 354 and 374 of sigma 2 and amino acids 1008 and 1031 of the beta subunit of the Escherichia coli DNA-dependent RNA polymerase. We suggest that the regions with similar sequence in sigma 2 and the beta subunit form amphipathic alpha-helices which may play a related role in the function of each protein. We have also performed experiments to further characterize the double-stranded RNA-binding activity of sigma 2 and found that the capacity to bind double-stranded RNA is a property of the sigma 2 protein of prototype strains and of the S2 mutant tsC447.     

Virulent aggregates of Streptococcus pyogenes are generated by homophilic protein-protein interactions

Many strains of the important human pathogen Streptococcus pyogenes form aggregates when grown in vitro in liquid medium. The present studies demonstrate that this property is crucial for the adherence, the resistance to phagocytosis and the virulence of S. pyogenes. A conserved sequence of 19 amino acid residues (designated AHP) was identified in surface proteins of common S. pyogenes serotypes. This sequence was found to promote bacterial aggregation through homophilic protein-protein interactions between AHP-containing surface proteins of neighbouring bacteria. A synthetic AHP peptide inhibited S. pyogenes aggregation, reduced the survival of S. pyogenes in human blood and attenuated its virulence in mice. In contrast, mutant bacteria devoid of surface proteins containing AHP-related sequences did not aggregate or adhere to epithelial cells. These bacteria are also rapidly killed in human blood and show reduced virulence in mice, underlining the pathogenic significance of the AHP sequence and S. pyogenes aggregation.     

白纹伊蚊细胞色素P450 CYP6家族基因多样性的研究(英文)

根据已获得的白纹伊蚊CYP6家族某成员cDNA序列片段AEDR ,设计基因特异性引物 ,以白纹伊蚊总RNA为模板 ,进行cDNA末端快速扩增 ,扩增产物经T -A克隆、测序。结果显示 :通过 5’ RACE获得 1个非全长cDNA序列 (GZS331 ) ,其与CYP6N1、CYP6N2的同源性分别为 59 8%和 59 1 % ,与CYP6N3v1 -v3同源性最高 ,达 83 9% - 84 3% ;通过 3’ RACE获得 6个非全长cDNA序列 ,其中来自抗性株的GZG0 33序列与CYP6N3v1 -v3的同源性达 98 2 % - 99 1 % ,而其余 3’ RACE克隆与CYP6N3v1 -v3的同源性则达 84 3% - 85 6%。上述所有非全长cDNA序列均与哺乳动物CYP3A1以及夜蛾CYP9A1有较高的同源性 ,分别为 2 3% - 36 1 %和 2 7 6% - 34 1 %。用PC/GENE软件所绘制的系统树显示出与同源性分析相一致的结果。所得非全长cDNA序列上报国际P450命名委员会进行统一的命名 ,并对蚊虫中细胞色素P450基因多样性及其形成原因进行了分析     

Alpha-factor structural gene mutations in Saccharomyces cerevisiae: effects on alpha-factor production and mating.

The role of alpha-factor structural genes MF alpha 1 and MF alpha 2 in alpha-factor production and mating has been investigated by the construction of mf alpha 1 and mf alpha 2 mutations that totally eliminate gene function. An mf alpha 1 mutant in which the entire coding region is deleted shows a considerable decrease in alpha-factor production and a 75% decrease in mating. Mutations in mf alpha 2 have little or no effect on alpha-factor production or mating. The mf alpha 1 mf alpha 2 double mutants are completely defective in mating and alpha-factor production. These results indicate that at least one alpha-factor structural gene product is required for mating in MAT alpha cells, that MF alpha 1 is responsible for the majority of alpha-factor production, and that MF alpha 1 and MF alpha 2 are the only active alpha-factor genes.     

Sequence diversity within the reovirus S2 gene: reovirus genes reassort in nature, and their termini are predicted to form a panhandle motif.

To better understand genetic diversity within mammalian reoviruses, we determined S2 nucleotide and deduced sigma 2 amino acid sequences of nine reovirus strains and compared these sequences with those of prototype strains of the three reovirus serotypes. The S2 gene and sigma 2 protein are highly conserved among the four type 1, one type 2, and seven type 3 strains studied. Phylogenetic analyses based on S2 nucleotide sequences of the 12 reovirus strains indicate that diversity within the S2 gene is independent of viral serotype. Additionally, we found marked topological differences between phylogenetic trees generated from S1 and S2 gene nucleotide sequences of the seven type 3 strains. These results demonstrate that reovirus S1 and S2 genes have distinct evolutionary histories, thus providing phylogenetic evidence for lateral transfer of reovirus genes in nature. When variability among the 12 sigma 2-encoding S2 nucleotide sequences was analyzed at synonymous positions, we found that approximately 60 nucleotides at the 5' terminus and 30 nucleotides at the 3' terminus were markedly conserved in comparison with other sigma 2-encoding regions of S2. Predictions of RNA secondary structures indicate that the more conserved S2 sequences participate in the formation of an extended region of duplex RNA interrupted by a pair of stem-loops. Among the 12 deduced sigma 2 amino acid sequences examined, substitutions were observed at only 11% of amino acid positions. This finding suggests that constraints on the structure or function of sigma 2, perhaps in part because of its location in the virion core, have limited sequence diversity within this protein.     

Multiple nonidentical reductive-dehalogenase-homologous genes are common in Dehalococcoides

Degenerate primers were used to amplify large fragments of reductive-dehalogenase-homologous (RDH) genes from genomic DNA of two Dehalococcoides populations, the chlorobenzene- and dioxin-dechlorinating strain CBDB1 and the trichloroethene-dechlorinating strain FL2. The amplicons (1,350 to 1,495 bp) corresponded to nearly complete open reading frames of known reductive dehalogenase genes and short fragments (approximately 90 bp) of genes encoding putative membrane-anchoring proteins. Cloning and restriction analysis revealed the presence of at least 14 different RDH genes in each strain. All amplified RDH genes showed sequence similarity with known reductive dehalogenase genes over the whole length of the sequence and shared all characteristics described for reductive dehalogenases. Deduced amino acid sequences of seven RDH genes from strain CBDB1 were 98.5 to 100% identical to seven different RDH genes from strain FL2, suggesting that both strains have an overlapping substrate range. All RDH genes identified in strains CBDB1 and FL2 were related to the RDH genes present in the genomes of Dehalococcoides ethenogenes strain 195 and Dehalococcoides sp. strain BAV1; however, sequence identity did not exceed 94.4 and 93.1%, respectively. The presence of RDH genes in strains CBDB1, FL2, and BAV1 that have no orthologs in strain 195 suggests that these strains possess dechlorination activities not present in strain 195. Comparative sequence analysis identified consensus sequences for cobalamin binding in deduced amino acid sequences of seven RDH genes. In conclusion, this study demonstrates that the presence of multiple nonidentical RDH genes is characteristic of Dehalococcoides strains.     

Saccharomyces cerevisiae contains two discrete genes coding for the alpha-factor pheromone.

Two genes, MF alpha 1 and MF alpha 2, coding for the alpha-factor in yeast Saccharomyces cerevisiae were identified by in situ colony hybridization of synthetic probes to a yeast genomic library. The probes were designed on the basis of the known amino acid sequence of the tridecapeptide alpha-pheromone. The nucleotide sequence revealed that the two genes, though similar in their overall structure, differ from each other in several striking ways. MF alpha 1 gene contains 4 copies of the coding sequence for the alpha-factor, which are separated by 24 nucleotides encoding the octapeptide Lys-Arg-Glu-Ala-Glu(or Asp)-Ala-Glu-Ala. The first alpha-factor coding block is preceded by a sequence for the hexapeptide Lys-Arg-Glu-Ala and 83 additional amino acids. MF alpha 2 gene contains coding sequences for two copies of the alpha-factor that differ from each other and from alpha-factor encoded by MF alpha 1 gene by a Gln leads to Asn and a Lys leads to Arg substitution. The first copy of the alpha-factor is preceded by a sequence coding for 87 amino acids which ends with Lys-Arg-Glu-Ala-Val-Ala-Asp-Ala. The coding blocks of the two copies of the pheromone are separated by the sequence for Lys-Arg-Glu-Ala-Asn-Ala-Asp-Ala. Thus, the alpha-factor can be derived from 2 different precursor proteins of 165 and 120 amino acids containing, respectively, 4 and 2 copies of the pheromone.     

Identification and characterization of two temperature-induced surface-associated proteins of Streptococcus suis with high homologies to members of the Arginine Deiminase system of Streptococcus pyogenes

The present study was performed to identify stress-induced putative virulence proteins of Streptococcus suis. For this, protein expression patterns of streptococci grown at 32, 37, and 42 degrees C were compared by one- and two-dimensional gel electrophoresis. Temperature shifts from 32 and 37 to 42 degrees C induced expression of two cell wall-associated proteins with apparent molecular masses of approximately 47 and 53 kDa. Amino-terminal sequence analysis of the two proteins indicated homologies of the 47-kDa protein with an ornithine carbamoyltransferase (OCT) from Streptococcus pyogenes and of the 53-kDa protein with the streptococcal acid glycoprotein (SAGP) from S. pyogenes, an arginine deiminase (AD) recently proposed as a putative virulence factor. Cloning and sequencing the genes encoding the putative OCT and AD of S. suis, octS and adiS, respectively, revealed that they had 81.2 (octS) and 80.2% (adiS) identity with the respective genes of S. pyogenes. Both genes belong to the AD system, also found in other bacteria. Southern hybridization analysis demonstrated the presence of the adiS gene in all 42 serotype 2 and 9 S. suis strains tested. In 9 of these 42 strains, selected randomly, we confirmed expression of the AdiS protein, homologous to SAGP, by immunoblot analysis using a specific antiserum against the SAGP of S. pyogenes. In all strains AD activity was detected. Furthermore, by immunoelectron microscopy using the anti-S. pyogenes SAGP antiserum we were able to demonstrate that the AdiS protein is expressed on the streptococcal surface in association with the capsular polysaccharides but is not coexpressed with them.     

Characterization of cryptic flagellin genes in Shigella boydii and Shigella dysenteriae.

Flagellin (fliC) genes of 12 Shigella boydii and five Shigella dysenteriae strains were characterized. Though these strains are nonmotile, the cryptic fliCSB gene, cloned from S. boydii strain C3, is functional for expression of flagellin. It consists of 1,704 bp, and encodes 568 amino acid residues (57,918 Da). The fliCSD gene from S. dysenteriae strain 16 consists of 1,650 bp encoding 549 amino acid residues (57,591 Da) and contains an IS1 element inserted in its 3' end. The two genes are composed of the 5'-constant, central variable and 3'-constant sequences, like other known fliC genes. The two genes share high homology in nucleotide and amino acid sequences with each other and also with the Escherichia coli fliCE gene, indicating that both genes are closely related to the fliCE gene. Comparison of the central variable sequences of six different fliC genes showed that the fliCSB and fliCSD genes share low homology in amino acid sequence with the other fliC genes, suggesting that they encode antigenic determinants intrinsic to respective subgroups. However, Southern blotting using as probes the central variable sequences of several fliC genes showed that four of 12 S. boydii strains have a fliC gene similar to that of Shigella flexneri, and that among five fliC genes from S. dysenteriae strains, one is similar to that of S. flexneri, two are similar to that of S. boydii, and only one is unique to S. dysenteriae. Some of these variant alleles were verified by immunoblotting with flagellins produced from cloned fliC genes. The presence of variant fliC alleles in S. boydii and S. dysenteriae indicates that subdivision into subgroups does not reflect the ancestral flagella H antigenic relationships. These data will be useful in considering the evolutionary divergence of the Shigella spp..     

Multiple Nonidentical Reductive-Dehalogenase-Homologous Genes Are Common in Dehalococcoides

Degenerate primers were used to amplify large fragments of reductive-dehalogenase-homologous (RDH) genes from genomic DNA of two Dehalococcoides populations, the chlorobenzene- and dioxin-dechlorinating strain CBDB1 and the trichloroethene-dechlorinating strain FL2. The amplicons (1,350 to 1,495 bp) corresponded to nearly complete open reading frames of known reductive dehalogenase genes and short fragments (approximately 90 bp) of genes encoding putative membrane-anchoring proteins. Cloning and restriction analysis revealed the presence of at least 14 different RDH genes in each strain. All amplified RDH genes showed sequence similarity with known reductive dehalogenase genes over the whole length of the sequence and shared all characteristics described for reductive dehalogenases. Deduced amino acid sequences of seven RDH genes from strain CBDB1 were 98.5 to 100% identical to seven different RDH genes from strain FL2, suggesting that both strains have an overlapping substrate range. All RDH genes identified in strains CBDB1 and FL2 were related to the RDH genes present in the genomes of Dehalococcoides ethenogenes strain 195 and Dehalococcoides sp. strain BAV1; however, sequence identity did not exceed 94.4 and 93.1%, respectively. The presence of RDH genes in strains CBDB1, FL2, and BAV1 that have no orthologs in strain 195 suggests that these strains possess dechlorination activities not present in strain 195. Comparative sequence analysis identified consensus sequences for cobalamin binding in deduced amino acid sequences of seven RDH genes. In conclusion, this study demonstrates that the presence of multiple nonidentical RDH genes is characteristic of Dehalococcoides strains.     

Serum opacity factor is a major fibronectin-binding protein and a virulence determinant of M type 2 Streptococcus pyogenes

Serum opacity factor (SOF) is a fibronectin-binding protein of group A streptococci that opacifies mammalian sera and is expressed by some strains that cause impetigo, pharyngitis and acute glomerulonephritis. Although SOF is expressed by approximately 35% of known serotypes, its role in the pathogenesis of group A streptococcal infections has not been previously investigated. The sof genes from M types 2, 28 and 49 Streptococcus pyogenes were cloned, sequenced, and their deduced amino acid sequences were compared. The gene for FnBA, a fibronectin-binding protein from Streptococcus dysgalactiae, was also cloned and found to express an opacity factor. The leader sequences, the fibronectin-binding domains, and the membrane anchor regions of these proteins were highly conserved. Short spans of conserved sequences were interspersed throughout the remaining parts of the proteins. The sof2 gene was insertionally inactivated in an M type 2 S. pyogenes strain, T2MR. The resultant SOF-negative mutant (YL3) did not express SOF or opacify serum, and exhibited a 71% reduction in binding fibronectin. Complementation of the SOF-negative defect with sof28 in the recombinant strain YL3(pNZ28) fully restored fibronectin-binding activity and the ability to opacify serum. To determine whether sof plays a role in virulence, mice were challenged intraperitoneally with these strains. None of the 10 mice infected with YL3(pNZ28) survived and only 1 out of 15 mice challenged with T2MR survived, whereas 12 out of 15 mice infected with YL3 survived. These data clearly indicate that SOF is a virulence factor, and they provide the first direct evidence that a fibronectin-binding protein contributes to the pathogenesis of group A streptococcal infections in vivo.     

Characterization of a Bacteroides mobilizable transposon, NBU2, which carries a functional lincomycin resistance gene

The mobilizable Bacteroides element NBU2 (11 kbp) was found originally in two Bacteroides clinical isolates, Bacteroides fragilis ERL and B. thetaiotaomicron DOT. At first, NBU2 appeared to be very similar to another mobilizable Bacteroides element, NBU1, in a 2.5-kbp internal region, but further examination of the full DNA sequence of NBU2 now reveals that the region of near identity between NBU1 and NBU2 is limited to this small region and that, outside this region, there is little sequence similarity between the two elements. The integrase gene of NBU2, intN2, was located at one end of the element. This gene was necessary and sufficient for the integration of NBU2. The integrase of NBU2 has the conserved amino acids (R-H-R-Y) in the C-terminal end that are found in members of the lambda family of site-specific integrases. This was also the only region in which the NBU1 and NBU2 integrases shared any similarity (28% amino acid sequence identity and 49% sequence similarity). Integration of NBU2 was site specific in Bacteroides species. Integration occurred in two primary sites in B. thetaiotaomicron. Both of these sites were located in the 3' end of a serine-tRNA gene NBU2 also integrated in Escherichia coli, but integration was much less site specific than in B. thetaiotaomicron. Analysis of the sequence of NBU2 revealed two potential antibiotic resistance genes. The amino acid sequences of the putative proteins encoded by these genes had similarity to resistances found in gram-positive bacteria. Only one of these genes was expressed in B. thetaiotaomicron, the homolog of linA, a lincomycin resistance gene from Staphylococcus aureus. To determine how widespread elements related to NBU1 and NBU2 are in Bacteroides species, we screened 291 Bacteroides strains. Elements with some sequence similarity to NBU2 and NBU1 were widespread in Bacteroides strains, and the presence of linA(N) in Bacteroides strains was highly correlated with the presence of NBU2, suggesting that NBU2 has been responsible for the spread of this gene among Bacteroides strains. Our results suggest that the NBU-related elements form a large and heterogeneous family, whose members have similar integration mechanisms but have different target sites and differ in whether they carry resistance genes.     

Nucleotide sequence of Saccharomyces cerevisiae genes TRP2 and TRP3 encoding bifunctional anthranilate synthase: indole-3-glycerol phosphate synthase

Saccharomyces cerevisiae anthranilate synthase:indole-3-glycerol phosphate synthase is a multifunctional hetero-oligomeric enzyme encoded by genes TRP2 and TRP3. TRP2, encoding anthranilate synthase Component I, was cloned by complementation of a yeast trp2 mutant. The nucleotide sequence of TRP2 as well as that of TRP3 were determined. The deduced anthranilate synthase Component I primary structure from yeast exhibits only limited similarity to that of the corresponding Escherichia coli subunit encoded by trpE. On the other hand, yeast anthranilate synthase Component II and indole-3-glycerol phosphate synthase amino acid sequences from TRP3 are clearly homologous with the corresponding sequences of the E. coli trpG and trpC polypeptide segments and thereby establish the bifunctional structure of TRP3 protein. Based on comparisons of TRP3 amino acid sequence with homologous sequences from E. coli and Neurospora crassa, an 11-amino acid residue connecting segment was identified which fuses the trpG and trpC functions of the bifunctional TRP3 protein chain. These comparisons support the conclusion that the amino acid sequence of connectors in homologous multifunctional enzymes need not be conserved. Connector function is thus not dependent on a specific sequence. Nuclease S1 mapping was used to identify mRNA 5' termini. Heterogeneous 5' termini were found for both TRP2 and TRP3 mRNA. TRP2 and TRP3 5'-flanking regions were analyzed for sequences that might function in regulation of these genes by the S. cerevisiae general amino acid control system. The 9 base pair direct repeat (Hinnebusch, A.G., and Fink, G.R. (1983) J. Biol. Chem. 258, 5238-5247) and inverted repeats were identified in the 5'-flanking sequences of TRP2 and TRP3.     

Beta-subunit of ATP-synthase: a useful marker for studying the phylogenetic relationship of eubacteria

The genes encoding the beta-subunits of ATP-synthases (ATPases) from Bacteroides fragilis DSM 2151, Cytophaga lytica DSM 2039 and 'Taxeobacter ocellatus' were cloned. The nucleotide sequences were determined completely for the genes of the first two organisms and to a major part for that of 'T. ocellatus'. The predicted amino acid sequences were compared with previously published amino acid sequences of beta-subunits. Two characteristic insertions were found in genes from organisms belonging to the so-called bacteroides-cytophaga-flavo-bacterium group. The remaining structure shows a high degree of sequence similarity within this group. These data support the conclusions drawn from comparative 16S rRNA sequence analyses that organisms in this phenotypically heterogeneous group are phylogenetically related. A phylogenetic tree was constructed based on a distance matrix of optimally aligned amino acid sequences of beta-subunits of ATPases of various eubacteria, chloroplasts and mitochondria. It is in good agreement with a tree derived from 16S rRNA sequence analyses.