The Detoxification of Nitric Oxide under Nitrogen Starvation

Abstract

Nitric oxide(NO) is a radical employed by many cells of the immune system to attack pathogens. The virulence of a number of bacterial pathogens is dependent on their ability to survive in the presence of NO. They must detoxify NO in environments that have multiple stressors, such as nutrient deprivation and acid stress. To explore the relationship between NO detoxification and nutrient starvation, the ability of E. coli to detoxify NO under nitrogen starvation was studied in aerobic cultures. We observed that nitrogen starvation has a graded effect on clearance. The longer cultures were placed in nitrogen absent media, the longer it took the cells to clear NO. But the relationship between starvation period and clearance time was not linear as cells were still able to clear NO fairly quickly after long periods of starvation. This is unlike the behavior seen in carbon source starvation, where both limitation of starvation of carbon led to an immediate failure to detoxify NO. Genes related to nitrogen metabolism and assimilation were deleted to understand the basis for this phenotype. The genes rpoS and rpoN were not found to be critical to the process of NO detoxification under short time nitrogen starvation. However, when relA was deleted, it significantly impaired the ability of cells to detoxify NO under short time starvation. This suggests that relA plays an important role in prioritizing NO detoxification upon nitrogen starvation.