SUMMARY
Capsular polysaccharide (CPS) is the outermost barrier between bacteria and their environment. It
shapes bacterial interactions with external factors, including adherence to surfaces (e.g. biofilm
formation, epithelial cell association); protection from environmental stressors (e.g., dehydration, UV
irradiation); susceptibility to predation (e.g., phage, bacteria, or amoeba); or immune evasion (e.g.
opsonophagocytosis). The Klebsiella species complex is comprised of non-fastidious Gram-negative
bacteria that colonize diverse environments, including soil, sewage, sink drains, and mammalian guts.
Klebsiella are early colonizers of the human gastrointestinal tract and, when environmental conditions
shift in the gut, they have the potential to bloom and out-compete all other colonizers, including closely
related Enterobacterales such as E. coli. Clearly, Klebsiella metabolic capacity is robust and flexible.
Moreover, Klebsiella CPS production is required for efficient gut colonization and persistence. There is
a major gap in our understanding of how exogenous signals are transduced through Klebsiella
metabolism and intracellular regulatory networks to control CPS production and how that CPS is
attached to the outer envelope. Our long-term goal is to understand how bacterial control of CPS
biosynthesis and attachment shapes fitness in response to changing environmental pressures at both
single cell and population levels. The objective of this application is to establish a model of the
exogenous and endogenous factors that control Klebsiella CPS biosynthesis and cell surface
attachment. We seek to establish a framework for understanding how Klebsiella and other Gram-
negative bacteria integrate exogenous nutrient signals with their metabolic and regulatory networks to
hone their fitness under varying environmental pressures. Recent progress in the laboratory has
identified specific genes and some environmental signals that alter CPS attachment and abundance.
Our proposed project areas are to examine (1) the mechanisms controlling CPS attachment and
release at the outer membrane and (2) how external nutrient sources and cellular metabolism regulate
CPS biosynthesis. The overall vision of our research program is to develop a model of how extracellular
signals combined with genetic and regulatory heterogeneity create dynamic surface exposed glycans
within a bacterial population to enhance overall fitness in the face of environmental challenges. This will
provide the foundation for identifying potential intervention points that could be targeted to modulate
bacterial CPS production and decolonize specific niches.