Pseudomonas syringae B728a
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Photo: Gordon Vrdoljak,
Electron Microscopy Laboratory, U.C. Berkeley

There are several compelling reasons for DOE to sequence Pseudomonas syringae. This is a very versatile organism with several important phenotypes that have made it a focus of study and commercial application that is relevant to the mission of DOE. This species is a plant pathogen, causing disease on a variety of plant species, severely impacting both food and biomass production. The DOE through its Energy Biosciences division has supported considerable work on basic aspects of virulence determinants in this pathogen over the years in labs such as that of Dr. Brian Staskawicz at Berkeley as well as other work at Cornell University, the University of Wisconsin, UC-Riverside, and elsewhere.

The DOE supported work has emphasized the gene-for-gene relationship that exists in this host-pathogen system and has led to the cloning of plant-disease resistance genes in tomato and other plants. The elucidation of the genome sequence of P. syringae would greatly aid such studies by better enabling new approaches to the study of coordinate gene expression in the pathogen in response to plant genotypic differences.

The DOE has also supported work on the elucidation of genes involved in stress tolerance of P. syringae in my lab at Berkeley for many years. Because this bacterium lives in stressful conditions on leaves there has been interest in finding those genetic determinants for stress tolerance that is enhanced in this species. The study of genes expressed in response to stresses on plants would be greatly advanced by the genome sequence of P. syringae. In addition, work at Berkeley has identified many genes which are expressed only when the bacterium is on plants. Such genes represent an extensive "hidden genome" that is unexplored because it is not expressed in culture. The availability of the genome sequence for P. syringae would greatly expand the ability to look at coordinate expression of such genes, in situ, such as by using microarray-based techniques.

Strains of P. syringae have also been exploited for a variety of industrial purposes of significance to DOE. For example, many strains of this species are active as ice nuclei catalyzing ice formation at temperatures approaching 0 C. For this reason they have been exploited as artificial ice nucleating agents in processes such as those involved in artificial snow production. A major use of the freeze-dried cells of P. syringae used in such an application has been in the creation of artificial ice islands to facilitate offshore oil drilling in cold oceans such as in the arctic. In a similar application there has been interest in using such ice nucleation active bacteria for the production of artificial mountains of ice in the winter for use in summer cooling of large industrial and office buildings. There is also considerable activity in the study of the use of such bacterial ice nuclei in improving the process of freezing of various foods, including frozen emulsified foods such as ice cream to improve both the energy efficiency of the process and quality of the product. Again, a more thorough knowledge of the genetics of P. syringae that would accompany a genomic sequence would help in exploiting this species for such uses.

Since the DOE has already initiated a Pseudomonas fluorescens genomic project, the sequencing of the Pseudomonas syringae genome would be of great value in a comparative analysis of these genomes. By comparing the genomes of these Pseudomonads with one another and with species such as Pseudomonas aeruginosa it should help establish which gene sets are unique to specialization in host or environmental niche. Thus the value of a given genomic sequence increases dramatically with the number of related sequences that are made available; P. syringae would make a good organism to compare with these other Pseudomonas.