Magnesium Promotes Flagellation ofVibrio fischeri

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Abstract
The bacteriumVibrio fischerirequires bacterial motility to initiate colonization of the Hawaiian squidEuprymna scolopes. Once colonized, however, the bacterial population becomes largely unflagellated. To understand environmental influences onV. fischerimotility, we investigated migration of this organism in tryptone-based soft agar media supplemented with different salts. We found that optimal migration required divalent cations and, in particular, Mg2+. At concentrations naturally present in seawater, Mg2+improved migration without altering the growth rate of the cells. Transmission electron microscopy and Western blot experiments suggested that Mg2+addition enhanced flagellation, at least in part through an effect on the steady-state levels of flagellin protein.