FIGURE 2.

Illustration of interspecies interactions between Streptococcus gordonii and its co-residents Actinomyces naeslundii and Actinobacillusactinomycetemcomitans. S. gordonii benefits from its coaggregation with A. naeslundii both in tolerating protein oxidation by H₂O₂ and in upregulating arginine biosynthesis. A. actinomycetemcomitans utilizes L-lactate, a carbohydrate metabolic by-product of S. gordonii as nutrient source. The consumption of lactic acid by the lactic acid-utilizing bacteria minimizes lactic acid accumulation, which otherwise would inhibit streptococcal growth. S. gordonii-generated H₂O₂ can stimulate activation of the A. actinomycetemcomitans OxyR regulator to increase transcription of apiA that leads to enhanced resistance to host innate immunity. The arrow in combination with + indicates stimulation. Model compiled from Brown and Whiteley (2007), Jakubovics et al. (2008a, b), and Ramsey and Whiteley (2009).