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.