Expression of Formate-Tetrahydrofolate Ligase Did Not Improve Growth but Interferes With Nitrogen and Carbon Metabolism of Synechocystis sp. PCC 6803

Abstract

The introduction of alternative CO 2-fixing pathways in photoautotrophic organism may improve the efficiency of biological carbon fixation such as minimizing the carbon loss due to photorespiration. Here, we analyzed the effects of creating a formate entry point into the primary metabolism of the cyanobacterium Synechocystis sp. PCC 6803. The formate-tetrahydrofolate ligase (FTL) from Methylobacterium extorquens AM1 was expressed in Synechocystis to enable formate assimilation and reducing the loss of fixed carbon in the photorespiratory pathway. Transgenic strains accumulated serine and 3-phosphoglycerate, and consumed more 2-phosphoglycolate and glycine, which seemed to reflect an efficient utilization of formate. However, labeling experiments showed that the serine accumulation was not due to the expected incorporation of formate. Subsequent DNA-microarray analysis revealed profound changes in transcript abundance due to ftl expression. Transcriptome changes were observed in relation to serine and glycine metabolism, C1-metabolism and particularly nitrogen assimilation. The data implied that ftl expression interfered with the signaling the carbon/nitrogen ratio in Synechocystis. Our results indicate that the expression of new enzymes could have a severe impact on the cellular regulatory network, which potentially hinders the establishment of newly designed pathways.

Natural carbon fixation and advances in synthetic engineering for redesigning and creating new fixation pathways

“…The significant improvements in synthetic biology permit the engineering of novel functions and metabolic networks in heterotrophic microorganisms for innumerous biotechnological applications [178] , [179] , [180] , [181] , [182] . Novel genes mediating the CO 2 fixation pathway in autotrophic microorganisms may apply negative influences on the regulatory networks in cells, such as carbon/nitrogen metabolism; however, they have been widely used as chassis to express natural CO 2 -fixation pathways in the model heterotrophic microbes Escherichia coli and Saccharomyces cerevisiae [183] , [184] .…”

Recent Advances in Developing Artificial Autotrophic Microorganism for Reinforcing CO2 Fixation

“…Moreover, it is challenging to attempt genetic manipulation of autotrophic microorganisms owing to their unclear genetic background and the absence of genetic tools. Meanwhile, overexpressing new genes responsible for foreign CO 2 fixation pathway in autotrophic microorganisms may exert negative influences on regulatory networks in cells, such as carbon/nitrogen metabolism (Song et al, 2020). As model heterotrophs, E. coli and Saccharomyces cerevisiae have been widely used to serve as chassis to express natural CO 2 fixation routes (Antonovsky et al, 2017).…”