POWRE: Biological Role of Motility in Bacterial Wilt of Plants

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Many bacteria are able to move, using propeller-like structures called flagella. Although the ability to move towards or within a host confers a significant selective advantage on some animal pathogens, the role of bacterial motility in plant-associated microbes is not known. One motile plant pathogen, Ralstonia solanacearum, causes bacterial wilt disease of many diverse plant species. When R. solanacearum grows in laboratory culture, its cells are motile only at low cell densities, possibly corresponding to conditions the bacterium encounters in nature during the early stages of host plant invasion and colonization. The PI will test the hypothesis that motility contributes to the success of bacterial plant pathogens by creating a nonmotile mutant of R. solanacearum. Invasiveness of this nomnotile mutant will be quantified using a combination of realistic soil virulence assays, timed root dip assays, and microscopic analysis with marked mutant and wildtype strains. The hypothesis that this species is motile only during host plant invasion and early stages of colonization will be tested directly by assaying bacterial motility during growth in the plant xylem vessel and indirectly by measuring expression of motility genes during growth in the plant xylem vessel. This will determine whether R. solanacearum gene expression in culture reflects the behavior of the pathogen in its host. Measuring motility gene expression in two regulatory mutant backgrounds will determine how bacterial motility fits into R. solanacearum's complex gene expression network. This research will elucidate a critical stage in the life cycle of a cosmopolitan and flexible model pathogen.This proposal fits the POWRE Program guidelines in the following ways: a) it opens an entirely new line of research inquiry for the P.I.; b) the P.I. has substantial administrative responsibilities in the area of women and science (she is jointly appointed in the Plant Pathology and Women's Studies departments, and also serves as Faculty Director of the campus Women in Science and Engineering Program); and, c) the P.I. recently resumed her career after an interruption for family leave.