Summary, conclusions and recommendations - Transport of Multiple Escherichia Coli Transport in Saturated Porous Media - page 117

structures to bacterial attachment to aquifer media. To achieve this, a number of genes known
to be involved in initial attachment need to be targeted; these genes include fimH, afa, ompC,
slp, and surA, Also, the so-called Keio collection of single gene deletion mutants of all non-
essential genes of E. coli K-12 is recommended. The Keio collection uses E. coli K-12, and
therefore, the arrangement and expression of surface structures and their combined effect on
initial attachment is characteristic for E. coli K-12, but not necessarily characteristic for
initial attachment of (wild) E. coli strains found in the environment. It will therefore be
important to identify the presence of some (2 or 3) of the most important surface structures on
wild E. coli strains for environmentally relevant conditions. The expression of surface
structures is usually governed by complex pathways, involving a wide variety of genes. For
instance, for the assembly of the motor of flagella of E. coli , the controlled expression of
about 50 genes is required. The control is governed by various switch proteins and
mechanisms, which, on their turn, are influenced by the environment the cell is in.
To further understand the contribution of various cell surface structures on their transport and
retention in aquifers, future transport experiments must focus on field bacterial transport
experiments. This will offer a better understanding of the various environmental factors that
may affect bacterial transport in real-world environments.These factors may include
hydrochemical and geochemical controls excerted on transport, like DOC, presence of iron-
oxides, sedimentary organic carbon, and calcium carbonates. In addition, the role of dual
porosity or perhaps even fissure flow types of environments may be more adequately be
assessed under field conditions than under laboratory conditions.