Paloma Garrido Amador

• Nitric oxide (NO) is a small gaseous molecule with important functions in cell biology and atmospheric chemistry owed to its unique physical and chemical properties. Since its relevance in biology was established, research on NO has focused primarily on its roles as signaling molecule, cytotoxin, and metabolic intermediate. Indeed, as a free radical and highly reactive compound, NO is as a potent toxin that can inhibit microbial growth, however it also has a central position in the microbial nitrogen cycle as a key intermediate in processes such as denitrification, aerobic ammonia oxidation, anaerobic ammonium oxidation, and nitrite-dependent anaerobic methane oxidation. Additionally, NO is a very energy-rich molecule with a high redox potential (NO/N2O; E0’ = +1.175 V) and it may have played a key role in the evolution of life on early Earth and the bioenergetic pathways related to modern denitrification and aerobic respiration. During recent years, we have been presented with new roles of NO in the nitrogen cycle. It appears as if the focus of NO research has slowly started to change its course as we begin to recognize its potential as direct substrate for microbial growth. Given its important roles in past and present microbial life, we believe that there must be a plethora of microorganisms that are capable of growing on NO conversions. Therefore, the main goal of my PhD project was to challenge our understanding of NO as mere toxin and intermediate, and investigate its potential as direct energy source for microbial life, whether it is through known or novel biochemical reactions, and the microorganisms that use it for this purpose, using a combination of continuous and batch incubations, physiological experiments, and multi-OMIC analyses.