The CrP operon of Chlamydia psittaci and Chlamydia pneumoniae

Analysis of Chlamydia pneumoniae infection in mononuclear cells by reverse transcription-PCR targeted to chlamydial gene transcripts

Chlamydia pneumoniae (C. pneumoniae) is an important etiological agent of respiratory infections including pneumonia. C. pneumoniae DNA can be detected in peripheral blood mononuclear cells indicating that monocytes can assist the spread of infection to other anatomical sites. Persistent infection established at these sites could promote inflammation and enhance pathology. Thus, the mononuclear cells are in a strategic position in the development of persistent infection. To investigate the intracellular replication and fate of C. pneumoniae in mononuclear cells, we have established an in vitro model in the human Mono Mac 6 cell line. In the present study, we analyzed the transcription of 11 C. pneumoniae genes in Mono Mac 6 cells during infection by real-time RT-PCR. Our results suggest that the transcriptional profile of the studied genes in monocytes is different from that seen in epithelial cells. Furthermore, our study shows that genes related to secretion are transcribed, and secreted bacterial proteins are also translated during infection of monocytes, creating novel opportunities for the management of chlamydial infection of monocytes.

Phylogenetic comparison of the known Chlamydia trachomatis sigma(66) promoters across to Chlamydia pneumoniae and Chlamydia caviae identifies seven poorly conserved promoters

We used four different phylogenetic footprinting programs and the six chlamydial species with publicly available whole genome sequences to analyze the 12 known sigma(66) promoters of Chlamydia trachomatis that phylogenetically footprinted negative in our previous paper. The analysis showed that 7 of the 12 promoters were poorly conserved across C. trachomatis, Chlamydia pneumoniae and Chlamydia caviae. Interestingly, the associated gene sets for these seven promoters were homologs and the gene orders were well conserved across these three species. Additional phylogenetic footprinting, across different subsets from that used above, of the six publicly available whole chlamydial genome sequences and transcription initiation site mapping of chlamydial promoters was also performed. This analysis showed that two of the seven poorly conserved promoters, the promoters in the upstream regions of C. caviae ltuA and ltuB, were like Escherichia coli sigma(70) promoters. Therefore, these promoters are similar to the promoters of C. trachomatis ltuA and ltuB, as they are sigma(70)-like. Given the fact that 7 out of the 22 known sigma(66) promoters in C. trachomatis are poorly conserved across C. trachomatis, C. pneumoniae and C. caviae, we would like to suggest that many other chlamydial promoters are poorly conserved across these species.

Chlamydial type III secretion system is encoded on ten operons preceded by sigma 70-like promoter elements

Many gram-negative bacterial pathogens employ type III secretion systems for infectious processes. Chlamydiae are obligate intracellular bacteria that encode a conserved type III secretion system that is likely requisite for growth. Typically, genes encoding type III secretion systems are located in a single locus; however, for chlamydiae these genes are scattered throughout the genome. Little is known regarding the gene regulatory mechanisms for this essential virulence determinant. To facilitate identification of cis-acting transcriptional regulatory elements, the operon structure was determined. This analysis revealed 10 operons that contained 37 genes associated with the type III secretion system. Linkage within these operons suggests a role in type III secretion for each of these genes, including 13 genes encoding proteins with unknown function. The transcriptional start site for each operon was determined. In conjunction with promoter activity assays, this analysis revealed that the type III secretion system operons encode sigma(70)-like promoter elements. Transcriptional initiation by a sigma factor responsible for constitutive gene expression indicates that undefined activators or repressors regulate developmental stage-specific expression of chlamydial type III secretion system genes.

Characterization of integration host factor (IHF) binding upstream of the cysteine-rich protein operon (omcAB) promoter of Chlamydia trachomatis LGV serovar L2

Chlamydiae are bacterial parasites that carry out a distinct developmental cycle within host cells; however, the mechanisms by which these organisms regulate stage-specific gene expression are not known. We identified a DNA element located between nucleotide (nt) -135 and -90 upstream from the transcription start point of the late stage-specific CRP operon (omcAB) of Chlamydia trachomatis, to which a protein in extracts of chlamydiae harvested at 23 h after infection binds. A recombinant protein of C. trachomatis open reading frame (ORF) CT267, which is homologous to bacterial integration host factor (IHF) and the heat-unstable nucleoid protein (HU), bound to the same element and produced the same DNase I footprint as the protein in chlamydial extracts. Recombinant ORF CT267 protein bound with high affinity to the DNA element and induced a sharp bend in a DNA fragment containing the binding site, suggesting that ORF CT267 encodes a protein with IHF-like activity, and recombinant protein had a positive effect on in vitro transcription of the CRP operon. IHF-binding activity and IHF protein were detected in extracts of C. trachomatis during the early to intermediate phases of the late stage of the developmental cycle (between 17 and 30 h after infection), but were absent in the extreme late phase of the cycle and in the infectious form of chlamydiae. The presence of an IHF binding site upstream of the CRP operon and the presence of chlamydial IHF-like protein when late stage genes are transcribed suggests that the chlamydial IHF may play a role in stage-specific gene expression.

Sequence analysis of the omp2 region of Chlamydia psittaci strain GPIC: structural and functional implications

The nucleotide sequence of a 3.1-kb genomic DNA fragment carrying the omp3, omp2 and srp gene homologs from Chlamydia psittaci strain GPIC was determined. A comparative analysis of the GPIC sequence with other chlamydial omp2-linked sequences reveals highly conserved omp3 and omp2 upstream sequences across species, suggesting a unified mechanism of transcription regulation. In contrast, the omp2-srp intergenic segment, which encompasses hypothetical srp transcriptional initiation sites, is relatively less conserved in length and in sequence. Examination of the predicted translation products reveals a high degree of homology within Omp3 and Omp2 across species, with the notable exception of the N-terminal fifth of Omp2. Although the latter segment displays relatively high interspecies sequence variation, it includes a smaller segment, whose high positive charge density is conserved across species, suggesting a conserved structure/function. In contrast to Omp2 and Omp3, a comparative analysis of the predicted amino acid (aa) sequence of the srp product reveals high homology within species, but relatively little across species. A 38-aa segment near the C-terminus of Srp, whose sequence is 64% identical between C. psittaci GPIC and C. trachomatis, is partially truncated in C. psittaci 6BC.