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Systemic movement by Clavibacter michiganensis subsp. michiganensis in the tomato vasculature
M. A. TANCOS (1), C. D. Smart (2). (1) Cornell Univ, Geneva, NY, U.S.A.; (2) Cornell University NYSAES, Geneva, NY, U.S.A.

The Gram-positive bacterium <i>Clavibacter michiganensis </i>subsp<i>. michiganensis</i> is an economically devastating seed-disseminated pathogen causing bacterial canker of tomato.  Historically, <i>C. michiganensis </i>subsp<i>. michiganensis</i> has been characterized as being non-motile; however, preliminary <i>in planta</i> experiments have demonstrated basipetal movement.  In order to complement the <i>in vivo</i> studies, microfluidic chambers were utilized to mimic xylem vessels by providing a flow rate similar to that <i>in planta</i>.  When observed in microfluidic chambers, non-flagellated <i>C. michiganensis </i>subsp<i>. michiganensis</i> actively moved against the media flow at speeds averaging 6 µm/min, which were similar to speeds observed <i>in planta</i>.  In addition to possible motility, systemic movement of <i>C. michiganensis </i>subsp<i>. michiganensis</i> is facilitated by the exploitation of nutrients.  Interestingly, <i>C. michiganensis </i>subsp<i>. michiganensis </i>and a small number of vascular-colonizing bacteria possess putative expansin proteins that share high structural similarity to expansins found in plants. These proteins are found in the plant cell wall and are involved in cell wall loosening during cell growth. The function of the bacterial expansin remains unknown, but is hypothesized to play a role in colonization and nutrient acquisition.  Therefore, a <i>C. michiganensis </i>subsp<i>. michiganensis</i> putative expansin gene was explored at both a microscopic and genetic level in order to better understand the role in pathogenesis.

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