Distinct morphological changes associated with the complex development cycle of the obligate intracellular bacterial pathogen Chlamydia trachomatis have been historically well characterized by microscopy. A number of temporally regulated genes have been characterized previously, suggesting that the chlamydial developmental cycle is regulated at the transcriptional level. This hypothesis was tested by microarray analysis in which the entire C. trachomatis genome was analyzed, providing a comprehensive assessment of global gene regulation throughout the chlamydial developmental cycle. Seven temporally cohesive gene clusters were identified, with 22% (189 genes) of the genome differentially expressed during the developmental cycle. The correlation of these gene clusters with hallmark morphological events of the chlamydial developmental cycle suggests three global stage-specific networks of gene regulation.

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BackgroundThe genus Bordetella consists of nine species that include important respiratory pathogens such as the ‘classical’ species B. bronchiseptica, B. pertussis and B. parapertussis and six more distantly related and less extensively studied species. Here we analyze sequence diversity and gene content of 128 genome sequences from all nine species with focus on the evolution of virulence-associated factors.ResultsBoth genome-wide sequence-based and gene content-based phylogenetic trees divide the genus into three species clades. The phylogenies are congruent between species suggesting genus-wide co-evolution of sequence diversity and gene content, but less correlated within species, mainly because of strain-specific presence of many different prophages. We compared the genomes with focus on virulence-associated genes and identified multiple clade-specific, species-specific and strain-specific events of gene acquisition and gene loss, including genes encoding O-antigens, protein secretion systems and bacterial toxins. Gene loss was more frequent than gene gain throughout the evolution, and loss of hundreds of genes was associated with the origin of several species, including the recently evolved human-restricted B. pertussis and B. holmesii, B. parapertussis and the avian pathogen B. avium.ConclusionsAcquisition and loss of multiple genes drive the evolution and speciation in the genus Bordetella, including large scale gene loss associated with the origin of several species. Recent loss and functional inactivation of genes, including those encoding pertussis vaccine components and bacterial toxins, in individual strains emphasize ongoing evolution.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-016-3112-5) contains supplementary material, which is available to authorized users.