Denitrification in low oxic environments increases the accumulation of nitrogen oxide intermediates and modulates the evolutionary potential of microbial populations

Denitrification in oxic environments occurs when a microorganism uses nitrogen oxides as terminal electron acceptors even though oxygen is available. While this phenomenon is well-established, its consequences on ecological and evolutionary processes remain poorly understood. We hypothesize here that denitrification in oxic environments can modify the accumulation profiles of nitrogen oxide intermediates with cascading effects on the evolutionary potentials of denitrifying microorganisms. To test this, we performed laboratory experiments with Paracoccus denitrificans and complemented them with individual-based computational modelling. We found that denitrification in low oxic environments significantly increases the accumulation of nitrite and nitric oxide. We further found that the increased accumulation of these intermediates has a negative effect on growth at low pH. Finally, we found that the increased negative effect at low pH increases the number of individuals that contribute to surface-associated growth. This increases the amount of genetic diversity that is preserved from the initial population, thus increasing the number of genetic targets for natural selection to act upon and resulting in higher evolutionary potentials. Together, our data highlight that denitrification in low oxic environments can affect the ecological processes and evolutionary potentials of denitrifying microorganisms by modifying the accumulation of nitrogen oxide intermediates. We show that denitrification in low oxic environments increases the accumulation of nitrite and nitric oxide intermediates. At low pH, the toxicity of these intermediates reduces the rate of growth and increases the number of individuals that contribute to surface-associated growth. This increases the amount of genetic diversity that is preserved during surface-associated growth, thus increasing the number of genetic targets for natural selection to act upon and resulting in higher evolutionary potentials.image

Automated summary

Denitrification in low oxic environments can increase the accumulation of nitrite and nitric oxide intermediates, which have negative effects on growth, especially at low pH. This process also increases the number of individuals contributing to surface-associated growth, resulting in higher genetic diversity and evolutionary potentials for denitrifying microorganisms.