U.S. Department of Energy

Pacific Northwest National Laboratory

Proteomics Reveals 408 Proteins Necessary for Cell Growth in Photosynthesis

The photosynthesis gene cluster in R. palustris.

The Science                      

Researchers used gene sequencing on the bacteria Rhodopseudomonas palustristo determine which genes are absolutely necessary for phototrophic growth. 

The Impact

The list of genes identified in the study as being essential for phototrophic growth provides a resource for researchers investigating photosynthesis and the conversion of light to energy. The list includes known photosynthetic and metabolic genes and hypothetical genes whose role in the process is currently ill-defined.


Phototrophic alphaproteobacteria, also known as purple non-sulphur bacteria, are found in terrestrial soil and water environments. They’re a class of highly-diverse bacteria that have little in common. It is the bacteria’s diversity that allows researchers to analyze the proteins necessary for photosynthesis.

Purple non-sulphur bacteria are important models for studying photophosphorylation, the process of using energy from sunlight for photosynthesis. These bacteria are facultative phototrophs—that is, they can obtain energy two ways: anaerobically from light or aerobically from respiring oxygen.

In this study, researchers at the Pacific Northwest National Laboratory helped their lead-author colleagues at the University of Washington by providing proteomics data and analyses using instrumentation at the Environmental Molecular Sciences Laboratory.

Specifically, researchers used transposon directed mutagenesis (a method to disrupt genes) to identify 167 proteins in the purple non-sulphur bacteria that are necessary for a cell to grow photosynthetically. And orthogonal proteomics data was used to identify 408 proteins that are significantly up-regulated in photosynthetic growth. Some of the proteins are well-known; the function of others remains a mystery.


This work was supported by a grant from the U.S. Army Research Office. The PNNL researchers were supported by the DOE BER 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 Northwest National Laboratory. 


CS Harwood, et al. “Genes essential for phototrophic growth by a purple alphaproteobacterium.” Environmental Microbiology(2017) 19(9), 3567–3578. doi:10.1111/1462-2920.13852 

July 2017
| Pacific Northwest National Laboratory