Abstract
Aggregatibacter actinomycetemcomitans genome can be divided into an accessory gene pool (found in some but not all strains) and a core gene pool (found in all strains). The functions of the accessory genes (genomic islands and non-island accessory genes) are largely unknown. We hypothesize that accessory genes confer critical functions for A. actinomycetemcomitans in vivo. This study examined the expression patterns of accessory and core genes of A. actinomycetemcomitans in distinct growth conditions. We found similar expression patterns of island and non-island accessory genes, which were generally lower than the core genes in all growth conditions. The median expression levels of genomic islands were 29%–37% of the core genes in enriched medium but elevated to as high as 63% of the core genes in nutrient-limited media. Several putative virulence genes, including the cytolethal distending toxin operon, were found to be activated in nutrient-limited conditions. In conclusion, genomic islands and non-island accessory genes exhibited distinct patterns of expression from the core genes and may play a role in the survival of A. actinomycetemcomitans in nutrient-limited environments.
Highlights
Gram-negative facultative A. actinomycetemcomitans is an oral commensal bacterium and a major causative agent of periodontitis, as well as an occasional cause of extra-oral infections [1,2,3,4]
As a first step to probe the functions of genomic islands and other non-island accessory genes, this study examined the patterns of gene expression of A. actinomycetemcomitans in different growth conditions
The results showed that genomic islands and non-island accessory genes exhibited similar patterns of gene expression, and exhibited lower levels of expression than core genes in all growth conditions
Summary
Gram-negative facultative A. actinomycetemcomitans is an oral commensal bacterium and a major causative agent of periodontitis, as well as an occasional cause of extra-oral infections [1,2,3,4]. The species comprises genetically heterogeneous strains that display differential association with periodontal health, disease, or disease progression, suggesting a pattern of strain-dependent virulence potentials including an example of a well-characterized highly leukotoxic JP2 type [5,6,7,8,9]. Beyond disease-association, genetically distinct A. actinomycetemcomitans strains are expected to be phenotypically distinct, which has been observed but not fully investigated [7,8,10,11]. Pathogens 2019, 8, 282 have different patterns of microbial associations, which may be indicative of differences in phenotypes and preferred niches. Within A. actinomycetemcomitans, strains of different clades may differ by as much as 20% in their genomic content. Large scale genomic rearrangements have been noted among A. actinomycetemcomitans strains of different clades [15]
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