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Abstract

Bacteria experience changes in their environment and have developed
various strategies to respond accordingly. To accommodate environmental
changes, certain bacteria differentiate between specialized cell types.
Vibrio parahaemolyticus is a marine bacterium, a worldwide human
pathogen and the leading agent of seafood-borne gastroenteritis. It
exists as swimmer or swarmer cells, specialized for life in liquid and
on solid environments, respectively. Swarmer cells are
characteristically highly elongated-a morphology important for swarming
behavior. When attached to surfaces it forms swarm colonies, however, it
is not known how cells within swarming populations respond to changes in
the external milieu and how its distinct life cycle influences its
ecological dissemination. The worldwide distribution of V.
parahaemolyticus accentuates the need for understanding the factors
contributing to its dissemination. Here we determine the stage-wise
development of swarm colonies and show how the swarm colony architecture
fluctuates with changing environmental conditions. Swarm colonies act as
a continuous source of cells that are released from the swarm colony
into the environment. Surprisingly, the cell length distribution of
released cells was very homogenous and almost no long cells were
detected, indicating that swarmer cells are not released into the liquid
environment but stay surface attached during flooding. Released cells
comprise a distinct cell type that is morphologically optimized for
swimming behavior and is capable of spreading in the liquid environment
and attach to new surfaces. Release of this distinct cell type
facilitates the dissemination of V. parahaemolyticus in the environment
and likely influences the ecology of this bacterium.