Altering NO emissions by manipulating wheat root bacterial community.

Nitrous oxide (NO) is a greenhouse gas and a potent ozone-depleting substance in the stratosphere. Agricultural soils are one of the main global sources of NO emissions, particularly from cereal fields due to their high areal coverage. The aim of this study was to isolate NO-reducing bacteria able to mitigate NO emissions from the soil after inoculation. We isolated several bacteria from wheat roots that were capable of NO reduction in vitro and studied their genetic potential and activity under different environmental conditions. Three of these isolates- all carrying the nitrous oxide reductase-encoding clade I nosZ, able to reduce NO in vitro, and efficient colonizers of wheat roots- presented different NO-reduction strategies when growing in the root zone, possibly due to the different conditions in situ and their metabolic preferences. Each isolate seemed to prefer to operate at different altered oxygen levels. Isolate AU243 (related to Agrobacterium/Rhizobium) could reduce both nitrate and NO and operated better at lower oxygen levels. Isolate AU14 (related to Alcaligenes faecalis), lacking nitrate reductases, operated better under less anoxic conditions. Isolate NT128 (related to Pseudomonas stutzeri) caused slightly increased NO emissions under both anoxic and ambient conditions. These results therefore emphasize the importance of a deep understanding of soil-plant-microbe interactions when environmental application is being considered.