(723f) Investigating The Critical Dimensions Of Bacterial Transport

We investigate the transport of bacteria through sub-micron
channels by using polydimethylsiloxane (PDMS) microfluidic devices. It is
important to understand how bacteria move through confined spaces, toward
certain chemicals and away from others, and whether they will continue to
advance toward the source when the confinement becomes smaller than their own dimensions.
The results obtained here will reveal more about bacterial behavior in soil
environments where the surroundings resemble micro- and nano-pores.

To determine the critical dimension for bacterial
migration, PDMS devices containing micro- and nanochannels were made using
replica molding. Initial master molds were created using a combination of
electron-beam and photolithography. The devices are very simple in their design.
They include a series of sub-micron channels in various sizes and geometric
shapes that connect large (approximately 10 x 100 micrometer) microfluidic channels
to a central main channel. By varying constriction geometries it is possible to
control where bacteria go in the devices. The bacteria are loaded into the main
channel while fresh food is loaded into the side channels, creating a gradient
along the sub-micron constrictions.

In this study, we used fluorescently labeled Bacillus
subtilis and Escherichia coli, which are prevalent in soil and
studied extensively in research laboratories. A chemotactic
response was imposed on the cells by filling the main channel containing bacteria
with phosphate buffered saline while the side channels were filled with
Lysogeny Broth (LB). Images taken with fluorescent microscope show that
bacteria quickly move toward the food source and form biofilms when the
dimensions of the constrictions approach the diameter of the bacteria cells. When
the cross-sectional area of the constrictions is significantly smaller than the
cell dimensions, cells attach themselves at the constriction entrance. An
interesting observation is that the cells were able to deform and squeeze
through constrictions where only one dimension is smaller than their diameter, for
example 0.7 x 1.5 micrometer.

These simple devices can be used to elucidate and understand
the complex interactions between microbial species in the environment. We will next
investigate the chemotactic response of microbes to other chemical compounds.