The pathogenic Gram-negative have evolved sophisticated tools to deliver
a myriad of proteins to various compartments of cell or external milieu.
The secreted proteins contribute to pathogenicity such as they could be
used to modulate their host environment, particularly, during
interaction with large hosts like humans and animals in a competing and
challenging environment. Protein secretion, in the case of Gram-negative
bacteria, involves translocation across the inner (plasma) as well as
the outer membrane. Thus several protein secretion systems include
dedicated apparatus to translocate proteins across the plasma and
outer-membranes of the bacteria. These secretion systems have been
classified into different categories which will be described here in
details. In this book, we discuss protein secretion pathways evolved
specifically in the Gram-negative bacteria; the; their representative
substrates including their synthesis, signal peptides, targeting, final
conformation, folding and what is known currently about their functions,
and role of each system in bacterial virulence and fitness is described.