The facultative chemolithoautotrophic gram negative bacteria Ralstonia eutropha is able to fix CO2 using the highly energy-demanding Calvin-Benson-Bassham cycle. RuBisCO is the main enzyme involved in CO2 fixation.
Despite RuBisCO’s affinity to CO2, its promiscuous activity with oxygen results in the formation of 2-phosphoglycolate. This side activity of RuBisCO generally reduces maximum autotrophic growth yields by approximately 25%. Processes required to metabolize 2-phosphoglycolate further are refer to as photorespiratory pathways. The aims of this work are (i) to determine the native photorespiratory pathways in R. eutropha, and (ii) removal of wasteful photorespiration pathways to create a platform strain for testing synthetic, potentially more efficient pathways for photorespiration.
It was possible to determine that the glycerate pathway seems to be the main route for photorespiration, while some other routes may play an additional role, including a decarboxylative pathway via malate synthase. The latter route has not been observed before to play a role in photorespiration.
Interestingly, pathways involved in photorespiration do not play equally important roles for growth on glycolate as sole carbon source. Therefore, additional analysis are required in order to better identify all the pathways involved in this process and try to determine the relative fluxes of each route.