Tn-seq was used to identify genes essential for phototrophic growth by the purple bacterium Rhodopseudomonas palustris. About 167 genes required for anaerobic growth on acetate in light were identified, 35 of which are annotated as photosynthesis genes. The essentiality of many of these genes by analysing the phenotypes of independently generated mutants that had altered pigmentation was verified. Three genes were identified, two possibly involved in biogenesis of the membrane-bound photosynthetic apparatus and one for phosphatidylcholine biosynthesis, that were not known to be essential for phototrophic growth. Site-directed mutagenesis was used to show that the NADH:quinone oxidoreductase complex IE was essential for phototrophic growth under strictly anaerobic conditions and appeared to play a role in reverse electron transport to generate NADH. A homologous NADH:quinone oxidoreductase complex IA likely operates in the opposite direction to oxidize NADH. The operation of the two enzymes in opposition would allow R. palustris to maintain redox balance. As a complement to the genetic data, proteomics experiments were carried out in which it was found that 408 proteins were present in significantly higher amounts in cells grown anaerobically in light compared with aerobically. Among these were proteins encoded by subset of the phototrophic growth-essential genes.
Bibliographical noteFunding Information:
This work was supported by grant W911NF-15-1-0150 from the U.S. Army Research Office. SHP and ESN were supported by the U.S. Department of Energy, Office of Biological and Environmental Research, Early Career Research Program. Mass spectrometry data was generated in the Environmental Molecular Science Laboratory, a U.S. Department of Energy (DOE) national scientific user facility at Pacific North-west National Laboratory (PNNL) in Richland, WA. Battelle operates PNNL for the DOE under contract DE-AC05-76RLO01830. This work was also supported by the grant of China Scholarship Council.